text: (function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports, require('d3-dsv'), require('topojson-client'), require('d3-time-format'), require('d3-array'), require('d3-shape'), require('d3-path'), require('d3-time'), require('d3-scale'), require('d3-interpolate'), require('d3-format'), require('d3-contour'), require('d3-geo'), require('d3-force'), require('d3-hierarchy'), require('d3-voronoi'), require('d3-color'), require('d3-timer')) :
    typeof define === 'function' && define.amd ? define(['exports', 'd3-dsv', 'topojson-client', 'd3-time-format', 'd3-array', 'd3-shape', 'd3-path', 'd3-time', 'd3-scale', 'd3-interpolate', 'd3-format', 'd3-contour', 'd3-geo', 'd3-force', 'd3-hierarchy', 'd3-voronoi', 'd3-color', 'd3-timer'], factory) :
    (global = global || self, factory(global.vega = {}, global.d3, global.topojson, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3, global.d3));
  }(this, function (exports, d3Dsv, topojsonClient, d3TimeFormat, d3Array, d3Shape, d3Path, d3Time, $$1, $$2, d3Format, d3Contour, d3Geo, d3Force, d3Hierarchy, d3Voronoi, d3Color, d3Timer) { 'use strict';
  
    function accessor(fn, fields, name) {
      fn.fields = fields || [];
      fn.fname = name;
      return fn;
    }
  
    function accessorName(fn) {
      return fn == null ? null : fn.fname;
    }
  
    function accessorFields(fn) {
      return fn == null ? null : fn.fields;
    }
  
    function error(message) {
      throw Error(message);
    }
  
    function splitAccessPath(p) {
      var path = [],
          q = null,
          b = 0,
          n = p.length,
          s = '',
          i, j, c;
  
      p = p + '';
  
      function push() {
        path.push(s + p.substring(i, j));
        s = '';
        i = j + 1;
      }
  
      for (i=j=0; j<n; ++j) {
        c = p[j];
        if (c === '\\') {
          s += p.substring(i, j);
          i = ++j;
        } else if (c === q) {
          push();
          q = null;
          b = -1;
        } else if (q) {
          continue;
        } else if (i === b && c === '"') {
          i = j + 1;
          q = c;
        } else if (i === b && c === "'") {
          i = j + 1;
          q = c;
        } else if (c === '.' && !b) {
          if (j > i) {
            push();
          } else {
            i = j + 1;
          }
        } else if (c === '[') {
          if (j > i) push();
          b = i = j + 1;
        } else if (c === ']') {
          if (!b) error('Access path missing open bracket: ' + p);
          if (b > 0) push();
          b = 0;
          i = j + 1;
        }
      }
  
      if (b) error('Access path missing closing bracket: ' + p);
      if (q) error('Access path missing closing quote: ' + p);
  
      if (j > i) {
        j++;
        push();
      }
  
      return path;
    }
  
    var isArray = Array.isArray;
  
    function isObject(_) {
      return _ === Object(_);
    }
  
    function isString(_) {
      return typeof _ === 'string';
    }
  
    function $(x) {
      return isArray(x) ? '[' + x.map($) + ']'
        : isObject(x) || isString(x) ?
          // Output valid JSON and JS source strings.
          // See http://timelessrepo.com/json-isnt-a-javascript-subset
          JSON.stringify(x).replace('\u2028','\\u2028').replace('\u2029', '\\u2029')
        : x;
    }
  
    function field(field, name) {
      var path = splitAccessPath(field),
          code = 'return _[' + path.map($).join('][') + '];';
  
      return accessor(
        Function('_', code),
        [(field = path.length===1 ? path[0] : field)],
        name || field
      );
    }
  
    var empty = [];
  
    var id = field('id');
  
    var identity = accessor(function(_) { return _; }, empty, 'identity');
  
    var zero = accessor(function() { return 0; }, empty, 'zero');
  
    var one = accessor(function() { return 1; }, empty, 'one');
  
    var truthy = accessor(function() { return true; }, empty, 'true');
  
    var falsy = accessor(function() { return false; }, empty, 'false');
  
    function log(method, level, input) {
      var msg = [level].concat([].slice.call(input));
      console[method](...msg); // eslint-disable-line no-console
    }
  
    var None  = 0;
    var Error$1 = 1;
    var Warn  = 2;
    var Info  = 3;
    var Debug = 4;
  
    function logger(_, method) {
      var level = _ || None;
      return {
        level: function(_) {
          if (arguments.length) {
            level = +_;
            return this;
          } else {
            return level;
          }
        },
        error: function() {
          if (level >= Error$1) log(method || 'error', 'ERROR', arguments);
          return this;
        },
        warn: function() {
          if (level >= Warn) log(method || 'warn', 'WARN', arguments);
          return this;
        },
        info: function() {
          if (level >= Info) log(method || 'log', 'INFO', arguments);
          return this;
        },
        debug: function() {
          if (level >= Debug) log(method || 'log', 'DEBUG', arguments);
          return this;
        }
      }
    }
  
    function peek(array) {
      return array[array.length - 1];
    }
  
    function toNumber(_) {
      return _ == null || _ === '' ? null : +_;
    }
  
    function exp(sign) {
      return function(x) { return sign * Math.exp(x); };
    }
  
    function log$1(sign) {
      return function(x) { return Math.log(sign * x); };
    }
  
    function symlog(c) {
      return function(x) { return Math.sign(x) * Math.log1p(Math.abs(x / c)); };
    }
  
    function symexp(c) {
      return function(x) { return Math.sign(x) * Math.expm1(Math.abs(x)) * c; };
    }
  
    function pow(exponent) {
      return function(x) {
        return x < 0 ? -Math.pow(-x, exponent) : Math.pow(x, exponent);
      };
    }
  
    function pan(domain, delta, lift, ground) {
      var d0 = lift(domain[0]),
          d1 = lift(peek(domain)),
          dd = (d1 - d0) * delta;
  
      return [
        ground(d0 - dd),
        ground(d1 - dd)
      ];
    }
  
    function panLinear(domain, delta) {
      return pan(domain, delta, toNumber, identity);
    }
  
    function panLog(domain, delta) {
      var sign = Math.sign(domain[0]);
      return pan(domain, delta, log$1(sign), exp(sign));
    }
  
    function panPow(domain, delta, exponent) {
      return pan(domain, delta, pow(exponent), pow(1/exponent));
    }
  
    function panSymlog(domain, delta, constant) {
      return pan(domain, delta, symlog(constant), symexp(constant));
    }
  
    function zoom(domain, anchor, scale, lift, ground) {
      var d0 = lift(domain[0]),
          d1 = lift(peek(domain)),
          da = anchor != null ? lift(anchor) : (d0 + d1) / 2;
  
      return [
        ground(da + (d0 - da) * scale),
        ground(da + (d1 - da) * scale)
      ];
    }
  
    function zoomLinear(domain, anchor, scale) {
      return zoom(domain, anchor, scale, toNumber, identity);
    }
  
    function zoomLog(domain, anchor, scale) {
      var sign = Math.sign(domain[0]);
      return zoom(domain, anchor, scale, log$1(sign), exp(sign));
    }
  
    function zoomPow(domain, anchor, scale, exponent) {
      return zoom(domain, anchor, scale, pow(exponent), pow(1/exponent));
    }
  
    function zoomSymlog(domain, anchor, scale, constant) {
      return zoom(domain, anchor, scale, symlog(constant), symexp(constant));
    }
  
    function quarter(date) {
      return 1 + ~~(new Date(date).getMonth() / 3);
    }
  
    function utcquarter(date) {
      return 1 + ~~(new Date(date).getUTCMonth() / 3);
    }
  
    function array(_) {
      return _ != null ? (isArray(_) ? _ : [_]) : [];
    }
  
    /**
     * Span-preserving range clamp. If the span of the input range is less
     * than (max - min) and an endpoint exceeds either the min or max value,
     * the range is translated such that the span is preserved and one
     * endpoint touches the boundary of the min/max range.
     * If the span exceeds (max - min), the range [min, max] is returned.
     */
    function clampRange(range, min, max) {
      var lo = range[0],
          hi = range[1],
          span;
  
      if (hi < lo) {
        span = hi;
        hi = lo;
        lo = span;
      }
      span = hi - lo;
  
      return span >= (max - min)
        ? [min, max]
        : [
            (lo = Math.min(Math.max(lo, min), max - span)),
            lo + span
          ];
    }
  
    function isFunction(_) {
      return typeof _ === 'function';
    }
  
    function compare(fields, orders) {
      var idx = [],
          cmp = (fields = array(fields)).map(function(f, i) {
            if (f == null) {
              return null;
            } else {
              idx.push(i);
              return isFunction(f) ? f
                : splitAccessPath(f).map($).join('][');
            }
          }),
          n = idx.length - 1,
          ord = array(orders),
          code = 'var u,v;return ',
          i, j, f, u, v, d, t, lt, gt;
  
      if (n < 0) return null;
  
      for (j=0; j<=n; ++j) {
        i = idx[j];
        f = cmp[i];
  
        if (isFunction(f)) {
          d = 'f' + i;
          u = '(u=this.' + d + '(a))';
          v = '(v=this.' + d + '(b))';
          (t = t || {})[d] = f;
        } else {
          u = '(u=a['+f+'])';
          v = '(v=b['+f+'])';
        }
  
        d = '((v=v instanceof Date?+v:v),(u=u instanceof Date?+u:u))';
  
        if (ord[i] !== 'descending') {
          gt = 1;
          lt = -1;
        } else {
          gt = -1;
          lt = 1;
        }
  
        code += '(' + u+'<'+v+'||u==null)&&v!=null?' + lt
          + ':(u>v||v==null)&&u!=null?' + gt
          + ':'+d+'!==u&&v===v?' + lt
          + ':v!==v&&u===u?' + gt
          + (i < n ? ':' : ':0');
      }
  
      f = Function('a', 'b', code + ';');
      if (t) f = f.bind(t);
  
      fields = fields.reduce(function(map, field) {
        if (isFunction(field)) {
          (accessorFields(field) || []).forEach(function(_) { map[_] = 1; });
        } else if (field != null) {
          map[field + ''] = 1;
        }
        return map;
      }, {});
  
      return accessor(f, Object.keys(fields));
    }
  
    function constant(_) {
      return isFunction(_) ? _ : function() { return _; };
    }
  
    function debounce(delay, handler) {
      var tid, evt;
  
      function callback() {
        handler(evt);
        tid = evt = null;
      }
  
      return function(e) {
        evt = e;
        if (tid) clearTimeout(tid);
        tid = setTimeout(callback, delay);
      };
    }
  
    function extend(_) {
      for (var x, k, i=1, len=arguments.length; i<len; ++i) {
        x = arguments[i];
        for (k in x) { _[k] = x[k]; }
      }
      return _;
    }
  
    /**
     * Return an array with minimum and maximum values, in the
     * form [min, max]. Ignores null, undefined, and NaN values.
     */
    function extent(array, f) {
      var i = 0, n, v, min, max;
  
      if (array && (n = array.length)) {
        if (f == null) {
          // find first valid value
          for (v = array[i]; v == null || v !== v; v = array[++i]);
          min = max = v;
  
          // visit all other values
          for (; i<n; ++i) {
            v = array[i];
            // skip null/undefined; NaN will fail all comparisons
            if (v != null) {
              if (v < min) min = v;
              if (v > max) max = v;
            }
          }
        } else {
          // find first valid value
          for (v = f(array[i]); v == null || v !== v; v = f(array[++i]));
          min = max = v;
  
          // visit all other values
          for (; i<n; ++i) {
            v = f(array[i]);
            // skip null/undefined; NaN will fail all comparisons
            if (v != null) {
              if (v < min) min = v;
              if (v > max) max = v;
            }
          }
        }
      }
  
      return [min, max];
    }
  
    function extentIndex(array, f) {
      var i = -1,
          n = array.length,
          a, b, c, u, v;
  
      if (f == null) {
        while (++i < n) {
          b = array[i];
          if (b != null && b >= b) {
            a = c = b;
            break;
          }
        }
        u = v = i;
        while (++i < n) {
          b = array[i];
          if (b != null) {
            if (a > b) {
              a = b;
              u = i;
            }
            if (c < b) {
              c = b;
              v = i;
            }
          }
        }
      } else {
        while (++i < n) {
          b = f(array[i], i, array);
          if (b != null && b >= b) {
            a = c = b;
            break;
          }
        }
        u = v = i;
        while (++i < n) {
          b = f(array[i], i, array);
          if (b != null) {
            if (a > b) {
              a = b;
              u = i;
            }
            if (c < b) {
              c = b;
              v = i;
            }
          }
        }
      }
  
      return [u, v];
    }
  
    var NULL = {};
  
    function fastmap(input) {
      var obj = {},
          map,
          test;
  
      function has(key) {
        return obj.hasOwnProperty(key) && obj[key] !== NULL;
      }
  
      map = {
        size: 0,
        empty: 0,
        object: obj,
        has: has,
        get: function(key) {
          return has(key) ? obj[key] : undefined;
        },
        set: function(key, value) {
          if (!has(key)) {
            ++map.size;
            if (obj[key] === NULL) --map.empty;
          }
          obj[key] = value;
          return this;
        },
        delete: function(key) {
          if (has(key)) {
            --map.size;
            ++map.empty;
            obj[key] = NULL;
          }
          return this;
        },
        clear: function() {
          map.size = map.empty = 0;
          map.object = obj = {};
        },
        test: function(_) {
          if (arguments.length) {
            test = _;
            return map;
          } else {
            return test;
          }
        },
        clean: function() {
          var next = {},
              size = 0,
              key, value;
          for (key in obj) {
            value = obj[key];
            if (value !== NULL && (!test || !test(value))) {
              next[key] = value;
              ++size;
            }
          }
          map.size = size;
          map.empty = 0;
          map.object = (obj = next);
        }
      };
  
      if (input) Object.keys(input).forEach(function(key) {
        map.set(key, input[key]);
      });
  
      return map;
    }
  
    function flush(range, value, threshold, left, right, center) {
      if (!threshold && threshold !== 0) return center;
  
      var a = range[0],
          b = peek(range),
          t = +threshold,
          l, r;
  
      // swap endpoints if range is reversed
      if (b < a) {
        l = a; a = b; b = l;
      }
  
      // compare value to endpoints
      l = Math.abs(value - a);
      r = Math.abs(b - value);
  
      // adjust if value is within threshold distance of endpoint
      return l < r && l <= t ? left : r <= t ? right : center;
    }
  
    function inherits(child, parent) {
      var proto = (child.prototype = Object.create(parent.prototype));
      proto.constructor = child;
      return proto;
    }
  
    /**
     * Predicate that returns true if the value lies within the span
     * of the given range. The left and right flags control the use
     * of inclusive (true) or exclusive (false) comparisons.
     */
    function inrange(value, range, left, right) {
      var r0 = range[0], r1 = range[range.length-1], t;
      if (r0 > r1) {
        t = r0;
        r0 = r1;
        r1 = t;
      }
      left = left === undefined || left;
      right = right === undefined || right;
  
      return (left ? r0 <= value : r0 < value) &&
        (right ? value <= r1 : value < r1);
    }
  
    function isBoolean(_) {
      return typeof _ === 'boolean';
    }
  
    function isDate(_) {
      return Object.prototype.toString.call(_) === '[object Date]';
    }
  
    function isNumber(_) {
      return typeof _ === 'number';
    }
  
    function isRegExp(_) {
      return Object.prototype.toString.call(_) === '[object RegExp]';
    }
  
    function key(fields, flat) {
      if (fields) {
        fields = flat
          ? array(fields).map(function(f) { return f.replace(/\\(.)/g, '$1'); })
          : array(fields);
      }
  
      var fn = !(fields && fields.length)
        ? function() { return ''; }
        : Function('_', 'return \'\'+' +
            fields.map(function(f) {
              return '_[' + (flat
                  ? $(f)
                  : splitAccessPath(f).map($).join('][')
                ) + ']';
            }).join('+\'|\'+') + ';');
  
      return accessor(fn, fields, 'key');
    }
  
    function lerp(array, frac) {
      const lo = array[0],
            hi = peek(array),
            f = +frac;
      return !f ? lo : f === 1 ? hi : lo + f * (hi - lo);
    }
  
    function merge(compare, array0, array1, output) {
      var n0 = array0.length,
          n1 = array1.length;
  
      if (!n1) return array0;
      if (!n0) return array1;
  
      var merged = output || new array0.constructor(n0 + n1),
          i0 = 0, i1 = 0, i = 0;
  
      for (; i0<n0 && i1<n1; ++i) {
        merged[i] = compare(array0[i0], array1[i1]) > 0
           ? array1[i1++]
           : array0[i0++];
      }
  
      for (; i0<n0; ++i0, ++i) {
        merged[i] = array0[i0];
      }
  
      for (; i1<n1; ++i1, ++i) {
        merged[i] = array1[i1];
      }
  
      return merged;
    }
  
    function repeat(str, reps) {
      var s = '';
      while (--reps >= 0) s += str;
      return s;
    }
  
    function pad(str, length, padchar, align) {
      var c = padchar || ' ',
          s = str + '',
          n = length - s.length;
  
      return n <= 0 ? s
        : align === 'left' ? repeat(c, n) + s
        : align === 'center' ? repeat(c, ~~(n/2)) + s + repeat(c, Math.ceil(n/2))
        : s + repeat(c, n);
    }
  
    /**
     * Return the numerical span of an array: the difference between
     * the last and first values.
     */
    function span(array) {
      return (peek(array) - array[0]) || 0;
    }
  
    function toBoolean(_) {
      return _ == null || _ === '' ? null : !_ || _ === 'false' || _ === '0' ? false : !!_;
    }
  
    function defaultParser(_) {
      return isNumber(_) ? _ : isDate(_) ? _ : Date.parse(_);
    }
  
    function toDate(_, parser) {
      parser = parser || defaultParser;
      return _ == null || _ === '' ? null : parser(_);
    }
  
    function toString(_) {
      return _ == null || _ === '' ? null : _ + '';
    }
  
    function toSet(_) {
      for (var s={}, i=0, n=_.length; i<n; ++i) s[_[i]] = true;
      return s;
    }
  
    function truncate(str, length, align, ellipsis) {
      var e = ellipsis != null ? ellipsis : '\u2026',
          s = str + '',
          n = s.length,
          l = Math.max(0, length - e.length);
  
      return n <= length ? s
        : align === 'left' ? e + s.slice(n - l)
        : align === 'center' ? s.slice(0, Math.ceil(l/2)) + e + s.slice(n - ~~(l/2))
        : s.slice(0, l) + e;
    }
  
    function visitArray(array, filter, visitor) {
      if (array) {
        var i = 0, n = array.length, t;
        if (filter) {
          for (; i<n; ++i) {
            if (t = filter(array[i])) visitor(t, i, array);
          }
        } else {
          array.forEach(visitor);
        }
      }
    }
  
    function UniqueList(idFunc) {
      var $ = idFunc || identity,
          list = [],
          ids = {};
  
      list.add = function(_) {
        var id = $(_);
        if (!ids[id]) {
          ids[id] = 1;
          list.push(_);
        }
        return list;
      };
  
      list.remove = function(_) {
        var id = $(_), idx;
        if (ids[id]) {
          ids[id] = 0;
          if ((idx = list.indexOf(_)) >= 0) {
            list.splice(idx, 1);
          }
        }
        return list;
      };
  
      return list;
    }
  
    /**
     * Invoke and await a potentially async callback function. If
     * an error occurs, trap it and route to Dataflow.error.
     * @param {Dataflow} df - The dataflow instance
     * @param {function} callback - A callback function to invoke
     *   and then await. The dataflow will be passed as the single
     *   argument to the function.
     */
    async function asyncCallback(df, callback) {
      try { await callback(df); } catch (err) { df.error(err); }
    }
  
    var TUPLE_ID_KEY = Symbol('vega_id'),
        TUPLE_ID = 1;
  
    /**
     * Checks if an input value is a registered tuple.
     * @param {*} t - The value to check.
     * @return {boolean} True if the input is a tuple, false otherwise.
     */
    function isTuple(t) {
      return !!(t && tupleid(t));
    }
  
    /**
     * Returns the id of a tuple.
     * @param {object} t - The input tuple.
     * @return {*} the tuple id.
     */
    function tupleid(t) {
      return t[TUPLE_ID_KEY];
    }
  
    /**
     * Sets the id of a tuple.
     * @param {object} t - The input tuple.
     * @param {*} id - The id value to set.
     * @return {object} the input tuple.
     */
    function setid(t, id) {
      t[TUPLE_ID_KEY] = id;
      return t;
    }
  
    /**
     * Ingest an object or value as a data tuple.
     * If the input value is an object, an id field will be added to it. For
     * efficiency, the input object is modified directly. A copy is not made.
     * If the input value is a literal, it will be wrapped in a new object
     * instance, with the value accessible as the 'data' property.
     * @param datum - The value to ingest.
     * @return {object} The ingested data tuple.
     */
    function ingest(datum) {
      var t = (datum === Object(datum)) ? datum : {data: datum};
      return tupleid(t) ? t : setid(t, TUPLE_ID++);
    }
  
    /**
     * Given a source tuple, return a derived copy.
     * @param {object} t - The source tuple.
     * @return {object} The derived tuple.
     */
    function derive(t) {
      return rederive(t, ingest({}));
    }
  
    /**
     * Rederive a derived tuple by copying values from the source tuple.
     * @param {object} t - The source tuple.
     * @param {object} d - The derived tuple.
     * @return {object} The derived tuple.
     */
    function rederive(t, d) {
      for (var k in t) d[k] = t[k];
      return d;
    }
  
    /**
     * Replace an existing tuple with a new tuple.
     * @param {object} t - The existing data tuple.
     * @param {object} d - The new tuple that replaces the old.
     * @return {object} The new tuple.
     */
    function replace(t, d) {
      return setid(d, tupleid(t));
    }
  
    function isChangeSet(v) {
      return v && v.constructor === changeset;
    }
  
    function changeset() {
      var add = [],  // insert tuples
          rem = [],  // remove tuples
          mod = [],  // modify tuples
          remp = [], // remove by predicate
          modp = [], // modify by predicate
          reflow = false;
  
      return {
        constructor: changeset,
        insert: function(t) {
          var d = array(t), i = 0, n = d.length;
          for (; i<n; ++i) add.push(d[i]);
          return this;
        },
        remove: function(t) {
          var a = isFunction(t) ? remp : rem,
              d = array(t), i = 0, n = d.length;
          for (; i<n; ++i) a.push(d[i]);
          return this;
        },
        modify: function(t, field, value) {
          var m = {field: field, value: constant(value)};
          if (isFunction(t)) {
            m.filter = t;
            modp.push(m);
          } else {
            m.tuple = t;
            mod.push(m);
          }
          return this;
        },
        encode: function(t, set) {
          if (isFunction(t)) modp.push({filter: t, field: set});
          else mod.push({tuple: t, field: set});
          return this;
        },
        reflow: function() {
          reflow = true;
          return this;
        },
        pulse: function(pulse, tuples) {
          var cur = {}, out = {}, i, n, m, f, t, id;
  
          // build lookup table of current tuples
          for (i=0, n=tuples.length; i<n; ++i) {
            cur[tupleid(tuples[i])] = 1;
          }
  
          // process individual tuples to remove
          for (i=0, n=rem.length; i<n; ++i) {
            t = rem[i];
            cur[tupleid(t)] = -1;
          }
  
          // process predicate-based removals
          for (i=0, n=remp.length; i<n; ++i) {
            f = remp[i];
            tuples.forEach(function(t) {
              if (f(t)) cur[tupleid(t)] = -1;
            });
          }
  
          // process all add tuples
          for (i=0, n=add.length; i<n; ++i) {
            t = add[i];
            id = tupleid(t);
            if (cur[id]) {
              // tuple already resides in dataset
              // if flagged for both add and remove, cancel
              cur[id] = 1;
            } else {
              // tuple does not reside in dataset, add
              pulse.add.push(ingest(add[i]));
            }
          }
  
          // populate pulse rem list
          for (i=0, n=tuples.length; i<n; ++i) {
            t = tuples[i];
            if (cur[tupleid(t)] < 0) pulse.rem.push(t);
          }
  
          // modify helper method
          function modify(t, f, v) {
            if (v) {
              t[f] = v(t);
            } else {
              pulse.encode = f;
            }
            if (!reflow) out[tupleid(t)] = t;
          }
  
          // process individual tuples to modify
          for (i=0, n=mod.length; i<n; ++i) {
            m = mod[i];
            t = m.tuple;
            f = m.field;
            id = cur[tupleid(t)];
            if (id > 0) {
              modify(t, f, m.value);
              pulse.modifies(f);
            }
          }
  
          // process predicate-based modifications
          for (i=0, n=modp.length; i<n; ++i) {
            m = modp[i];
            f = m.filter;
            tuples.forEach(function(t) {
              if (f(t) && cur[tupleid(t)] > 0) {
                modify(t, m.field, m.value);
              }
            });
            pulse.modifies(m.field);
          }
  
          // upon reflow request, populate mod with all non-removed tuples
          // otherwise, populate mod with modified tuples only
          if (reflow) {
            pulse.mod = rem.length || remp.length
              ? tuples.filter(function(t) { return cur[tupleid(t)] > 0; })
              : tuples.slice();
          } else {
            for (id in out) pulse.mod.push(out[id]);
          }
  
          return pulse;
        }
      };
    }
  
    var CACHE = '_:mod:_';
  
    /**
     * Hash that tracks modifications to assigned values.
     * Callers *must* use the set method to update values.
     */
    function Parameters() {
      Object.defineProperty(this, CACHE, {writable: true, value: {}});
    }
  
    var prototype = Parameters.prototype;
  
    /**
     * Set a parameter value. If the parameter value changes, the parameter
     * will be recorded as modified.
     * @param {string} name - The parameter name.
     * @param {number} index - The index into an array-value parameter. Ignored if
     *   the argument is undefined, null or less than zero.
     * @param {*} value - The parameter value to set.
     * @param {boolean} [force=false] - If true, records the parameter as modified
     *   even if the value is unchanged.
     * @return {Parameters} - This parameter object.
     */
    prototype.set = function(name, index, value, force) {
      var o = this,
          v = o[name],
          mod = o[CACHE];
  
      if (index != null && index >= 0) {
        if (v[index] !== value || force) {
          v[index] = value;
          mod[index + ':' + name] = -1;
          mod[name] = -1;
        }
      } else if (v !== value || force) {
        o[name] = value;
        mod[name] = isArray(value) ? 1 + value.length : -1;
      }
  
      return o;
    };
  
    /**
     * Tests if one or more parameters has been modified. If invoked with no
     * arguments, returns true if any parameter value has changed. If the first
     * argument is array, returns trues if any parameter name in the array has
     * changed. Otherwise, tests if the given name and optional array index has
     * changed.
     * @param {string} name - The parameter name to test.
     * @param {number} [index=undefined] - The parameter array index to test.
     * @return {boolean} - Returns true if a queried parameter was modified.
     */
    prototype.modified = function(name, index) {
      var mod = this[CACHE], k;
      if (!arguments.length) {
        for (k in mod) { if (mod[k]) return true; }
        return false;
      } else if (isArray(name)) {
        for (k=0; k<name.length; ++k) {
          if (mod[name[k]]) return true;
        }
        return false;
      }
      return (index != null && index >= 0)
        ? (index + 1 < mod[name] || !!mod[index + ':' + name])
        : !!mod[name];
    };
  
    /**
     * Clears the modification records. After calling this method,
     * all parameters are considered unmodified.
     */
    prototype.clear = function() {
      this[CACHE] = {};
      return this;
    };
  
    var OP_ID = 0;
    var PULSE = 'pulse';
    var NO_PARAMS = new Parameters();
  
    // Boolean Flags
    var SKIP     = 1,
        MODIFIED = 2;
  
    /**
     * An Operator is a processing node in a dataflow graph.
     * Each operator stores a value and an optional value update function.
     * Operators can accept a hash of named parameters. Parameter values can
     * either be direct (JavaScript literals, arrays, objects) or indirect
     * (other operators whose values will be pulled dynamically). Operators
     * included as parameters will have this operator added as a dependency.
     * @constructor
     * @param {*} [init] - The initial value for this operator.
     * @param {function(object, Pulse)} [update] - An update function. Upon
     *   evaluation of this operator, the update function will be invoked and the
     *   return value will be used as the new value of this operator.
     * @param {object} [params] - The parameters for this operator.
     * @param {boolean} [react=true] - Flag indicating if this operator should
     *   listen for changes to upstream operators included as parameters.
     * @see parameters
     */
    function Operator(init, update, params, react) {
      this.id = ++OP_ID;
      this.value = init;
      this.stamp = -1;
      this.rank = -1;
      this.qrank = -1;
      this.flags = 0;
  
      if (update) {
        this._update = update;
      }
      if (params) this.parameters(params, react);
    }
  
    var prototype$1 = Operator.prototype;
  
    /**
     * Returns a list of target operators dependent on this operator.
     * If this list does not exist, it is created and then returned.
     * @return {UniqueList}
     */
    prototype$1.targets = function() {
      return this._targets || (this._targets = UniqueList(id));
    };
  
    /**
     * Sets the value of this operator.
     * @param {*} value - the value to set.
     * @return {Number} Returns 1 if the operator value has changed
     *   according to strict equality, returns 0 otherwise.
     */
    prototype$1.set = function(value) {
      if (this.value !== value) {
        this.value = value;
        return 1;
      } else {
        return 0;
      }
    };
  
    function flag(bit) {
      return function(state) {
        var f = this.flags;
        if (arguments.length === 0) return !!(f & bit);
        this.flags = state ? (f | bit) : (f & ~bit);
        return this;
      };
    }
  
    /**
     * Indicates that operator evaluation should be skipped on the next pulse.
     * This operator will still propagate incoming pulses, but its update function
     * will not be invoked. The skip flag is reset after every pulse, so calling
     * this method will affect processing of the next pulse only.
     */
    prototype$1.skip = flag(SKIP);
  
    /**
     * Indicates that this operator's value has been modified on its most recent
     * pulse. Normally modification is checked via strict equality; however, in
     * some cases it is more efficient to update the internal state of an object.
     * In those cases, the modified flag can be used to trigger propagation. Once
     * set, the modification flag persists across pulses until unset. The flag can
     * be used with the last timestamp to test if a modification is recent.
     */
    prototype$1.modified = flag(MODIFIED);
  
    /**
     * Sets the parameters for this operator. The parameter values are analyzed for
     * operator instances. If found, this operator will be added as a dependency
     * of the parameterizing operator. Operator values are dynamically marshalled
     * from each operator parameter prior to evaluation. If a parameter value is
     * an array, the array will also be searched for Operator instances. However,
     * the search does not recurse into sub-arrays or object properties.
     * @param {object} params - A hash of operator parameters.
     * @param {boolean} [react=true] - A flag indicating if this operator should
     *   automatically update (react) when parameter values change. In other words,
     *   this flag determines if the operator registers itself as a listener on
     *   any upstream operators included in the parameters.
     * @param {boolean} [initonly=false] - A flag indicating if this operator
     *   should calculate an update only upon its initiatal evaluation, then
     *   deregister dependencies and suppress all future update invocations.
     * @return {Operator[]} - An array of upstream dependencies.
     */
    prototype$1.parameters = function(params, react, initonly) {
      react = react !== false;
      var self = this,
          argval = (self._argval = self._argval || new Parameters()),
          argops = (self._argops = self._argops || []),
          deps = [],
          name, value, n, i;
  
      function add(name, index, value) {
        if (value instanceof Operator) {
          if (value !== self) {
            if (react) value.targets().add(self);
            deps.push(value);
          }
          argops.push({op:value, name:name, index:index});
        } else {
          argval.set(name, index, value);
        }
      }
  
      for (name in params) {
        value = params[name];
  
        if (name === PULSE) {
          array(value).forEach(function(op) {
            if (!(op instanceof Operator)) {
              error('Pulse parameters must be operator instances.');
            } else if (op !== self) {
              op.targets().add(self);
              deps.push(op);
            }
          });
          self.source = value;
        } else if (isArray(value)) {
          argval.set(name, -1, Array(n = value.length));
          for (i=0; i<n; ++i) add(name, i, value[i]);
        } else {
          add(name, -1, value);
        }
      }
  
      this.marshall().clear(); // initialize values
      if (initonly) argops.initonly = true;
  
      return deps;
    };
  
    /**
     * Internal method for marshalling parameter values.
     * Visits each operator dependency to pull the latest value.
     * @return {Parameters} A Parameters object to pass to the update function.
     */
    prototype$1.marshall = function(stamp) {
      var argval = this._argval || NO_PARAMS,
          argops = this._argops, item, i, n, op, mod;
  
      if (argops) {
        for (i=0, n=argops.length; i<n; ++i) {
          item = argops[i];
          op = item.op;
          mod = op.modified() && op.stamp === stamp;
          argval.set(item.name, item.index, op.value, mod);
        }
  
        if (argops.initonly) {
          for (i=0; i<n; ++i) {
            item = argops[i];
            item.op.targets().remove(this);
          }
          this._argops = null;
          this._update = null;
        }
      }
      return argval;
    };
  
    /**
     * Delegate method to perform operator processing.
     * Subclasses can override this method to perform custom processing.
     * By default, it marshalls parameters and calls the update function
     * if that function is defined. If the update function does not
     * change the operator value then StopPropagation is returned.
     * If no update function is defined, this method does nothing.
     * @param {Pulse} pulse - the current dataflow pulse.
     * @return The output pulse or StopPropagation. A falsy return value
     *   (including undefined) will let the input pulse pass through.
     */
    prototype$1.evaluate = function(pulse) {
      var update = this._update;
      if (update) {
        var params = this.marshall(pulse.stamp),
            v = update.call(this, params, pulse);
  
        params.clear();
        if (v !== this.value) {
          this.value = v;
        } else if (!this.modified()) {
          return pulse.StopPropagation;
        }
      }
    };
  
    /**
     * Run this operator for the current pulse. If this operator has already
     * been run at (or after) the pulse timestamp, returns StopPropagation.
     * Internally, this method calls {@link evaluate} to perform processing.
     * If {@link evaluate} returns a falsy value, the input pulse is returned.
     * This method should NOT be overridden, instead overrride {@link evaluate}.
     * @param {Pulse} pulse - the current dataflow pulse.
     * @return the output pulse for this operator (or StopPropagation)
     */
    prototype$1.run = function(pulse) {
      if (pulse.stamp <= this.stamp) return pulse.StopPropagation;
      var rv;
      if (this.skip()) {
        this.skip(false);
        rv = 0;
      } else {
        rv = this.evaluate(pulse);
      }
      this.stamp = pulse.stamp;
      return (this.pulse = rv || pulse);
    };
  
    /**
     * Add an operator to the dataflow graph. This function accepts a
     * variety of input argument types. The basic signature supports an
     * initial value, update function and parameters. If the first parameter
     * is an Operator instance, it will be added directly. If it is a
     * constructor for an Operator subclass, a new instance will be instantiated.
     * Otherwise, if the first parameter is a function instance, it will be used
     * as the update function and a null initial value is assumed.
     * @param {*} init - One of: the operator to add, the initial value of
     *   the operator, an operator class to instantiate, or an update function.
     * @param {function} [update] - The operator update function.
     * @param {object} [params] - The operator parameters.
     * @param {boolean} [react=true] - Flag indicating if this operator should
     *   listen for changes to upstream operators included as parameters.
     * @return {Operator} - The added operator.
     */
    function add(init, update, params, react) {
      var shift = 1,
        op;
  
      if (init instanceof Operator) {
        op = init;
      } else if (init && init.prototype instanceof Operator) {
        op = new init();
      } else if (isFunction(init)) {
        op = new Operator(null, init);
      } else {
        shift = 0;
        op = new Operator(init, update);
      }
  
      this.rank(op);
      if (shift) {
        react = params;
        params = update;
      }
      if (params) this.connect(op, op.parameters(params, react));
      this.touch(op);
  
      return op;
    }
  
    /**
     * Connect a target operator as a dependent of source operators.
     * If necessary, this method will rerank the target operator and its
     * dependents to ensure propagation proceeds in a topologically sorted order.
     * @param {Operator} target - The target operator.
     * @param {Array<Operator>} - The source operators that should propagate
     *   to the target operator.
     */
    function connect(target, sources) {
      var targetRank = target.rank, i, n;
  
      for (i=0, n=sources.length; i<n; ++i) {
        if (targetRank < sources[i].rank) {
          this.rerank(target);
          return;
        }
      }
    }
  
    var STREAM_ID = 0;
  
    /**
     * Models an event stream.
     * @constructor
     * @param {function(Object, number): boolean} [filter] - Filter predicate.
     *   Events pass through when truthy, events are suppressed when falsy.
     * @param {function(Object): *} [apply] - Applied to input events to produce
     *   new event values.
     * @param {function(Object)} [receive] - Event callback function to invoke
     *   upon receipt of a new event. Use to override standard event processing.
     */
    function EventStream(filter, apply, receive) {
      this.id = ++STREAM_ID;
      this.value = null;
      if (receive) this.receive = receive;
      if (filter) this._filter = filter;
      if (apply) this._apply = apply;
    }
  
    /**
     * Creates a new event stream instance with the provided
     * (optional) filter, apply and receive functions.
     * @param {function(Object, number): boolean} [filter] - Filter predicate.
     *   Events pass through when truthy, events are suppressed when falsy.
     * @param {function(Object): *} [apply] - Applied to input events to produce
     *   new event values.
     * @see EventStream
     */
    function stream(filter, apply, receive) {
      return new EventStream(filter, apply, receive);
    }
  
    var prototype$2 = EventStream.prototype;
  
    prototype$2._filter = truthy;
  
    prototype$2._apply = identity;
  
    prototype$2.targets = function() {
      return this._targets || (this._targets = UniqueList(id));
    };
  
    prototype$2.consume = function(_) {
      if (!arguments.length) return !!this._consume;
      this._consume = !!_;
      return this;
    };
  
    prototype$2.receive = function(evt) {
      if (this._filter(evt)) {
        var val = (this.value = this._apply(evt)),
            trg = this._targets,
            n = trg ? trg.length : 0,
            i = 0;
  
        for (; i<n; ++i) trg[i].receive(val);
  
        if (this._consume) {
          evt.preventDefault();
          evt.stopPropagation();
        }
      }
    };
  
    prototype$2.filter = function(filter) {
      var s = stream(filter);
      this.targets().add(s);
      return s;
    };
  
    prototype$2.apply = function(apply) {
      var s = stream(null, apply);
      this.targets().add(s);
      return s;
    };
  
    prototype$2.merge = function() {
      var s = stream();
  
      this.targets().add(s);
      for (var i=0, n=arguments.length; i<n; ++i) {
        arguments[i].targets().add(s);
      }
  
      return s;
    };
  
    prototype$2.throttle = function(pause) {
      var t = -1;
      return this.filter(function() {
        var now = Date.now();
        if ((now - t) > pause) {
          t = now;
          return 1;
        } else {
          return 0;
        }
      });
    };
  
    prototype$2.debounce = function(delay) {
      var s = stream();
  
      this.targets().add(stream(null, null,
        debounce(delay, function(e) {
          var df = e.dataflow;
          s.receive(e);
          if (df && df.run) df.run();
        })
      ));
  
      return s;
    };
  
    prototype$2.between = function(a, b) {
      var active = false;
      a.targets().add(stream(null, null, function() { active = true; }));
      b.targets().add(stream(null, null, function() { active = false; }));
      return this.filter(function() { return active; });
    };
  
    /**
     * Create a new event stream from an event source.
     * @param {object} source - The event source to monitor. The input must
     *  support the addEventListener method.
     * @param {string} type - The event type.
     * @param {function(object): boolean} [filter] - Event filter function.
     * @param {function(object): *} [apply] - Event application function.
     *   If provided, this function will be invoked and the result will be
     *   used as the downstream event value.
     * @return {EventStream}
     */
    function events(source, type, filter, apply) {
      var df = this,
          s = stream(filter, apply),
          send = function(e) {
            e.dataflow = df;
            try {
              s.receive(e);
            } catch (error) {
              df.error(error);
            } finally {
              df.run();
            }
          },
          sources;
  
      if (typeof source === 'string' && typeof document !== 'undefined') {
        sources = document.querySelectorAll(source);
      } else {
        sources = array(source);
      }
  
      for (var i=0, n=sources.length; i<n; ++i) {
        sources[i].addEventListener(type, send);
      }
  
      return s;
    }
  
    // Matches absolute URLs with optional protocol
    //   https://...    file://...    //...
    const protocol_re = /^([A-Za-z]+:)?\/\//;
  
    // Matches allowed URIs. From https://github.com/cure53/DOMPurify/blob/master/src/regexp.js with added file://
    const allowed_re = /^(?:(?:(?:f|ht)tps?|mailto|tel|callto|cid|xmpp|file):|[^a-z]|[a-z+.\-]+(?:[^a-z+.\-:]|$))/i; // eslint-disable-line no-useless-escape
    const whitespace_re = /[\u0000-\u0020\u00A0\u1680\u180E\u2000-\u2029\u205f\u3000]/g; // eslint-disable-line no-control-regex
  
  
    // Special treatment in node.js for the file: protocol
    const fileProtocol = 'file://';
  
    /**
     * Factory for a loader constructor that provides methods for requesting
     * files from either the network or disk, and for sanitizing request URIs.
     * @param {function} fetch - The Fetch API for HTTP network requests.
     *   If null or undefined, HTTP loading will be disabled.
     * @param {object} fs - The file system interface for file loading.
     *   If null or undefined, local file loading will be disabled.
     * @return {function} A loader constructor with the following signature:
     *   param {object} [options] - Optional default loading options to use.
     *   return {object} - A new loader instance.
     */
    function loaderFactory(fetch, fs) {
      return function(options) {
        return {
          options: options || {},
          sanitize: sanitize,
          load: load,
          fileAccess: !!fs,
          file: fileLoader(fs),
          http: httpLoader(fetch)
        };
      };
    }
  
    /**
     * Load an external resource, typically either from the web or from the local
     * filesystem. This function uses {@link sanitize} to first sanitize the uri,
     * then calls either {@link http} (for web requests) or {@link file} (for
     * filesystem loading).
     * @param {string} uri - The resource indicator (e.g., URL or filename).
     * @param {object} [options] - Optional loading options. These options will
     *   override any existing default options.
     * @return {Promise} - A promise that resolves to the loaded content.
     */
    async function load(uri, options) {
      const opt = await this.sanitize(uri, options),
            url = opt.href;
  
      return opt.localFile
        ? this.file(url)
        : this.http(url, options);
    }
  
    /**
     * URI sanitizer function.
     * @param {string} uri - The uri (url or filename) to sanity check.
     * @param {object} options - An options hash.
     * @return {Promise} - A promise that resolves to an object containing
     *  sanitized uri data, or rejects it the input uri is deemed invalid.
     *  The properties of the resolved object are assumed to be
     *  valid attributes for an HTML 'a' tag. The sanitized uri *must* be
     *  provided by the 'href' property of the returned object.
     */
    async function sanitize(uri, options) {
      options = extend({}, this.options, options);
  
      const fileAccess = this.fileAccess,
            result = {href: null};
  
      let isFile, loadFile, base;
  
      const isAllowed = allowed_re.test(uri.replace(whitespace_re, ''));
  
      if (uri == null || typeof uri !== 'string' || !isAllowed) {
        error('Sanitize failure, invalid URI: ' + $(uri));
      }
  
      const hasProtocol = protocol_re.test(uri);
  
      // if relative url (no protocol/host), prepend baseURL
      if ((base = options.baseURL) && !hasProtocol) {
        // Ensure that there is a slash between the baseURL (e.g. hostname) and url
        if (!uri.startsWith('/') && base[base.length-1] !== '/') {
          uri = '/' + uri;
        }
        uri = base + uri;
      }
  
      // should we load from file system?
      loadFile = (isFile = uri.startsWith(fileProtocol))
        || options.mode === 'file'
        || options.mode !== 'http' && !hasProtocol && fileAccess;
  
      if (isFile) {
        // strip file protocol
        uri = uri.slice(fileProtocol.length);
      } else if (uri.startsWith('//')) {
        if (options.defaultProtocol === 'file') {
          // if is file, strip protocol and set loadFile flag
          uri = uri.slice(2);
          loadFile = true;
        } else {
          // if relative protocol (starts with '//'), prepend default protocol
          uri = (options.defaultProtocol || 'http') + ':' + uri;
        }
      }
  
      // set non-enumerable mode flag to indicate local file load
      Object.defineProperty(result, 'localFile', {value: !!loadFile});
  
      // set uri
      result.href = uri;
  
      // set default result target, if specified
      if (options.target) {
        result.target = options.target + '';
      }
  
      // set default result rel, if specified (#1542)
      if (options.rel) {
        result.rel = options.rel + '';
      }
  
      // return
      return result;
    }
  
    /**
     * File system loader factory.
     * @param {object} fs - The file system interface.
     * @return {function} - A file loader with the following signature:
     *   param {string} filename - The file system path to load.
     *   param {string} filename - The file system path to load.
     *   return {Promise} A promise that resolves to the file contents.
     */
    function fileLoader(fs) {
      return fs
        ? function(filename) {
            return new Promise(function(accept, reject) {
              fs.readFile(filename, function(error, data) {
                if (error) reject(error);
                else accept(data);
              });
            });
          }
        : fileReject;
    }
  
    /**
     * Default file system loader that simply rejects.
     */
    async function fileReject() {
      error('No file system access.');
    }
  
    /**
     * HTTP request handler factory.
     * @param {function} fetch - The Fetch API method.
     * @return {function} - An http loader with the following signature:
     *   param {string} url - The url to request.
     *   param {object} options - An options hash.
     *   return {Promise} - A promise that resolves to the file contents.
     */
    function httpLoader(fetch) {
      return fetch
        ? async function(url, options) {
            const opt = extend({}, this.options.http, options),
                  type = options && options.response,
                  response = await fetch(url, opt);
  
            return !response.ok
              ? error(response.status + '' + response.statusText)
              : isFunction(response[type]) ? response[type]()
              : response.text();
          }
        : httpReject;
    }
  
    /**
     * Default http request handler that simply rejects.
     */
    async function httpReject() {
      error('No HTTP fetch method available.');
    }
  
    var typeParsers = {
      boolean: toBoolean,
      integer: toNumber,
      number:  toNumber,
      date:    toDate,
      string:  toString,
      unknown: identity
    };
  
    var typeTests = [
      isBoolean$1,
      isInteger,
      isNumber$1,
      isDate$1
    ];
  
    var typeList = [
      'boolean',
      'integer',
      'number',
      'date'
    ];
  
    function inferType(values, field) {
      if (!values || !values.length) return 'unknown';
  
      var value, i, j, t = 0,
          n = values.length,
          m = typeTests.length,
          a = typeTests.map(function(_, i) { return i + 1; });
  
      for (i=0, n=values.length; i<n; ++i) {
        value = field ? values[i][field] : values[i];
        for (j=0; j<m; ++j) {
          if (a[j] && isValid(value) && !typeTests[j](value)) {
            a[j] = 0;
            ++t;
            if (t === typeTests.length) return 'string';
          }
        }
      }
  
      t = a.reduce(function(u, v) { return u === 0 ? v : u; }, 0) - 1;
      return typeList[t];
    }
  
    function inferTypes(data, fields) {
      return fields.reduce(function(types, field) {
        types[field] = inferType(data, field);
        return types;
      }, {});
    }
  
    // -- Type Checks ----
  
    function isValid(_) {
      return _ != null && _ === _;
    }
  
    function isBoolean$1(_) {
      return _ === 'true' || _ === 'false' || _ === true || _ === false;
    }
  
    function isDate$1(_) {
      return !isNaN(Date.parse(_));
    }
  
    function isNumber$1(_) {
      return !isNaN(+_) && !(_ instanceof Date);
    }
  
    function isInteger(_) {
      return isNumber$1(_) && (_=+_) === ~~_;
    }
  
    function delimitedFormat(delimiter) {
      const parse = function(data, format) {
        const delim = {delimiter: delimiter};
        return dsv(data, format ? extend(format, delim) : delim);
      };
  
      parse.responseType = 'text';
  
      return parse;
    }
  
    function dsv(data, format) {
      if (format.header) {
        data = format.header
          .map($)
          .join(format.delimiter) + '\n' + data;
      }
      return d3Dsv.dsvFormat(format.delimiter).parse(data + '');
    }
  
    dsv.responseType = 'text';
  
    function isBuffer(_) {
      return (typeof Buffer === 'function' && isFunction(Buffer.isBuffer))
        ? Buffer.isBuffer(_) : false;
    }
  
    function json(data, format) {
      const prop = (format && format.property) ? field(format.property) : identity;
      return isObject(data) && !isBuffer(data)
        ? parseJSON(prop(data))
        : prop(JSON.parse(data));
    }
  
    json.responseType = 'json';
  
    function parseJSON(data, format) {
      return (format && format.copy)
        ? JSON.parse(JSON.stringify(data))
        : data;
    }
  
    const filters = {
      interior: (a, b) => a !== b,
      exterior: (a, b) => a === b
    };
  
    function topojson(data, format) {
      let method, object, property, filter;
      data = json(data, format);
  
      if (format && format.feature) {
        method = topojsonClient.feature;
        property = format.feature;
      } else if (format && format.mesh) {
        method = topojsonClient.mesh;
        property = format.mesh;
        filter = filters[format.filter];
      } else {
        error('Missing TopoJSON feature or mesh parameter.');
      }
  
      object = (object = data.objects[property])
        ? method(data, object, filter)
        : error('Invalid TopoJSON object: ' + property);
  
      return object && object.features || [object];
    }
  
    topojson.responseType = 'json';
  
    const format = {
      dsv: dsv,
      csv: delimitedFormat(','),
      tsv: delimitedFormat('\t'),
      json: json,
      topojson: topojson
    };
  
    function formats(name, reader) {
      if (arguments.length > 1) {
        format[name] = reader;
        return this;
      } else {
        return format.hasOwnProperty(name) ? format[name] : null;
      }
    }
  
    function responseType(type) {
      const f = formats(type);
      return f && f.responseType || 'text';
    }
  
    function read(data, schema, dateParse) {
      schema = schema || {};
  
      const reader = formats(schema.type || 'json');
      if (!reader) error('Unknown data format type: ' + schema.type);
  
      data = reader(data, schema);
      if (schema.parse) parse(data, schema.parse, dateParse);
  
      if (data.hasOwnProperty('columns')) delete data.columns;
      return data;
    }
  
    function parse(data, types, dateParse) {
      if (!data.length) return; // early exit for empty data
  
      dateParse = dateParse || d3TimeFormat.timeParse;
  
      var fields = data.columns || Object.keys(data[0]),
          parsers, datum, field, i, j, n, m;
  
      if (types === 'auto') types = inferTypes(data, fields);
  
      fields = Object.keys(types);
      parsers = fields.map(function(field) {
        var type = types[field],
            parts, pattern;
  
        if (type && (type.indexOf('date:') === 0 || type.indexOf('utc:') === 0)) {
          parts = type.split(/:(.+)?/, 2);  // split on first :
          pattern = parts[1];
  
          if ((pattern[0] === '\'' && pattern[pattern.length-1] === '\'') ||
              (pattern[0] === '"'  && pattern[pattern.length-1] === '"')) {
            pattern = pattern.slice(1, -1);
          }
  
          return parts[0] === 'utc' ? d3TimeFormat.utcParse(pattern) : dateParse(pattern);
        }
  
        if (!typeParsers[type]) {
          throw Error('Illegal format pattern: ' + field + ':' + type);
        }
  
        return typeParsers[type];
      });
  
      for (i=0, n=data.length, m=fields.length; i<n; ++i) {
        datum = data[i];
        for (j=0; j<m; ++j) {
          field = fields[j];
          datum[field] = parsers[j](datum[field]);
        }
      }
    }
  
    var loader = loaderFactory(
      typeof fetch !== 'undefined' && fetch, // use built-in fetch API
      null // no file system access
    );
  
    const parse$1 = read;
  
    /**
     * Ingests new data into the dataflow. First parses the data using the
     * vega-loader read method, then pulses a changeset to the target operator.
     * @param {Operator} target - The Operator to target with ingested data,
     *   typically a Collect transform instance.
     * @param {*} data - The input data, prior to parsing. For JSON this may
     *   be a string or an object. For CSV, TSV, etc should be a string.
     * @param {object} format - The data format description for parsing
     *   loaded data. This object is passed to the vega-loader read method.
     * @returns {Dataflow}
     */
    function ingest$1(target, data, format) {
      return this.pulse(target, this.changeset().insert(parse$1(data, format)));
    }
  
    /**
     * Request data from an external source, parse it, and return a Promise.
     * @param {string} url - The URL from which to load the data. This string
     *   is passed to the vega-loader load method.
     * @param {object} [format] - The data format description for parsing
     *   loaded data. This object is passed to the vega-loader read method.
     * @return {Promise} A Promise that resolves upon completion of the request.
     *   The resolved object contains the following properties:
     *   - data: an array of parsed data (or null upon error)
     *   - status: a code for success (0), load fail (-1), or parse fail (-2)
     */
    async function request(url, format) {
      const df = this;
      let status = 0, data;
  
      try {
        data = await df.loader().load(url, {
          context: 'dataflow',
          response: responseType(format && format.type)
        });
        try {
          data = parse$1(data, format);
        } catch (err) {
          status = -2;
          df.warn('Data ingestion failed', url, err);
        }
      } catch (err) {
        status = -1;
        df.warn('Loading failed', url, err);
      }
  
      return {data, status};
    }
  
    async function preload(target, url, format) {
      const df = this,
            pending = df._pending || loadPending(df);
  
      pending.requests += 1;
  
      const res = await df.request(url, format);
      df.pulse(target, df.changeset().remove(truthy).insert(res.data || []));
  
      pending.done();
      return res;
    }
  
    function loadPending(df) {
      var pending = new Promise(function(a) { accept = a; }),
          accept;
  
      pending.requests = 0;
  
      pending.done = function() {
        if (--pending.requests === 0) {
          df._pending = null;
          accept(df);
        }
      };
  
      return (df._pending = pending);
    }
  
    var SKIP$1 = {skip: true};
  
    /**
     * Perform operator updates in response to events. Applies an
     * update function to compute a new operator value. If the update function
     * returns a {@link ChangeSet}, the operator will be pulsed with those tuple
     * changes. Otherwise, the operator value will be updated to the return value.
     * @param {EventStream|Operator} source - The event source to react to.
     *   This argument can be either an EventStream or an Operator.
     * @param {Operator|function(object):Operator} target - The operator to update.
     *   This argument can either be an Operator instance or (if the source
     *   argument is an EventStream), a function that accepts an event object as
     *   input and returns an Operator to target.
     * @param {function(Parameters,Event): *} [update] - Optional update function
     *   to compute the new operator value, or a literal value to set. Update
     *   functions expect to receive a parameter object and event as arguments.
     *   This function can either return a new operator value or (if the source
     *   argument is an EventStream) a {@link ChangeSet} instance to pulse
     *   the target operator with tuple changes.
     * @param {object} [params] - The update function parameters.
     * @param {object} [options] - Additional options hash. If not overridden,
     *   updated operators will be skipped by default.
     * @param {boolean} [options.skip] - If true, the operator will
     *  be skipped: it will not be evaluated, but its dependents will be.
     * @param {boolean} [options.force] - If true, the operator will
     *   be re-evaluated even if its value has not changed.
     * @return {Dataflow}
     */
    function on(source, target, update, params, options) {
      var fn = source instanceof Operator ? onOperator : onStream;
      fn(this, source, target, update, params, options);
      return this;
    }
  
    function onStream(df, stream, target, update, params, options) {
      var opt = extend({}, options, SKIP$1), func, op;
  
      if (!isFunction(target)) target = constant(target);
  
      if (update === undefined) {
        func = e => df.touch(target(e));
      } else if (isFunction(update)) {
        op = new Operator(null, update, params, false);
        func = e => {
          op.evaluate(e);
          const t = target(e), v = op.value;
          isChangeSet(v) ? df.pulse(t, v, options) : df.update(t, v, opt);
        };
      } else {
        func = e => df.update(target(e), update, opt);
      }
  
      stream.apply(func);
    }
  
    function onOperator(df, source, target, update, params, options) {
      if (update === undefined) {
        source.targets().add(target);
      } else {
        const opt = options || {},
              op = new Operator(null, updater(target, update), params, false);
        op.modified(opt.force);
        op.rank = source.rank;       // immediately follow source
        source.targets().add(op);    // add dependency
  
        if (target) {
          op.skip(true);             // skip first invocation
          op.value = target.value;   // initialize value
          op.targets().add(target);  // chain dependencies
          df.connect(target, [op]);  // rerank as needed, #1672
        }
      }
    }
  
    function updater(target, update) {
      update = isFunction(update) ? update : constant(update);
      return target
        ? function(_, pulse) {
            const value = update(_, pulse);
            if (!target.skip()) {
              target.skip(value !== this.value).value = value;
            }
            return value;
          }
        : update;
    }
  
    /**
     * Assigns a rank to an operator. Ranks are assigned in increasing order
     * by incrementing an internal rank counter.
     * @param {Operator} op - The operator to assign a rank.
     */
    function rank(op) {
      op.rank = ++this._rank;
    }
  
    /**
     * Re-ranks an operator and all downstream target dependencies. This
     * is necessary when upstream dependencies of higher rank are added to
     * a target operator.
     * @param {Operator} op - The operator to re-rank.
     */
    function rerank(op) {
      var queue = [op],
          cur, list, i;
  
      while (queue.length) {
        this.rank(cur = queue.pop());
        if (list = cur._targets) {
          for (i=list.length; --i >= 0;) {
            queue.push(cur = list[i]);
            if (cur === op) error('Cycle detected in dataflow graph.');
          }
        }
      }
    }
  
    /**
     * Sentinel value indicating pulse propagation should stop.
     */
    var StopPropagation = {};
  
    // Pulse visit type flags
    var ADD       = (1 << 0),
        REM       = (1 << 1),
        MOD       = (1 << 2),
        ADD_REM   = ADD | REM,
        ADD_MOD   = ADD | MOD,
        ALL       = ADD | REM | MOD,
        REFLOW    = (1 << 3),
        SOURCE    = (1 << 4),
        NO_SOURCE = (1 << 5),
        NO_FIELDS = (1 << 6);
  
    /**
     * A Pulse enables inter-operator communication during a run of the
     * dataflow graph. In addition to the current timestamp, a pulse may also
     * contain a change-set of added, removed or modified data tuples, as well as
     * a pointer to a full backing data source. Tuple change sets may not
     * be fully materialized; for example, to prevent needless array creation
     * a change set may include larger arrays and corresponding filter functions.
     * The pulse provides a {@link visit} method to enable proper and efficient
     * iteration over requested data tuples.
     *
     * In addition, each pulse can track modification flags for data tuple fields.
     * Responsible transform operators should call the {@link modifies} method to
     * indicate changes to data fields. The {@link modified} method enables
     * querying of this modification state.
     *
     * @constructor
     * @param {Dataflow} dataflow - The backing dataflow instance.
     * @param {number} stamp - The current propagation timestamp.
     * @param {string} [encode] - An optional encoding set name, which is then
     *   accessible as Pulse.encode. Operators can respond to (or ignore) this
     *   setting as appropriate. This parameter can be used in conjunction with
     *   the Encode transform in the vega-encode module.
     */
    function Pulse(dataflow, stamp, encode) {
      this.dataflow = dataflow;
      this.stamp = stamp == null ? -1 : stamp;
      this.add = [];
      this.rem = [];
      this.mod = [];
      this.fields = null;
      this.encode = encode || null;
    }
  
    var prototype$3 = Pulse.prototype;
  
    /**
     * Sentinel value indicating pulse propagation should stop.
     */
    prototype$3.StopPropagation = StopPropagation;
  
    /**
     * Boolean flag indicating ADD (added) tuples.
     */
    prototype$3.ADD = ADD;
  
    /**
     * Boolean flag indicating REM (removed) tuples.
     */
    prototype$3.REM = REM;
  
    /**
     * Boolean flag indicating MOD (modified) tuples.
     */
    prototype$3.MOD = MOD;
  
    /**
     * Boolean flag indicating ADD (added) and REM (removed) tuples.
     */
    prototype$3.ADD_REM = ADD_REM;
  
    /**
     * Boolean flag indicating ADD (added) and MOD (modified) tuples.
     */
    prototype$3.ADD_MOD = ADD_MOD;
  
    /**
     * Boolean flag indicating ADD, REM and MOD tuples.
     */
    prototype$3.ALL = ALL;
  
    /**
     * Boolean flag indicating all tuples in a data source
     * except for the ADD, REM and MOD tuples.
     */
    prototype$3.REFLOW = REFLOW;
  
    /**
     * Boolean flag indicating a 'pass-through' to a
     * backing data source, ignoring ADD, REM and MOD tuples.
     */
    prototype$3.SOURCE = SOURCE;
  
    /**
     * Boolean flag indicating that source data should be
     * suppressed when creating a forked pulse.
     */
    prototype$3.NO_SOURCE = NO_SOURCE;
  
    /**
     * Boolean flag indicating that field modifications should be
     * suppressed when creating a forked pulse.
     */
    prototype$3.NO_FIELDS = NO_FIELDS;
  
    /**
     * Creates a new pulse based on the values of this pulse.
     * The dataflow, time stamp and field modification values are copied over.
     * By default, new empty ADD, REM and MOD arrays are created.
     * @param {number} flags - Integer of boolean flags indicating which (if any)
     *   tuple arrays should be copied to the new pulse. The supported flag values
     *   are ADD, REM and MOD. Array references are copied directly: new array
     *   instances are not created.
     * @return {Pulse} - The forked pulse instance.
     * @see init
     */
    prototype$3.fork = function(flags) {
      return new Pulse(this.dataflow).init(this, flags);
    };
  
    /**
     * Creates a copy of this pulse with new materialized array
     * instances for the ADD, REM, MOD, and SOURCE arrays.
     * The dataflow, time stamp and field modification values are copied over.
     * @return {Pulse} - The cloned pulse instance.
     * @see init
     */
    prototype$3.clone = function() {
      var p = this.fork(ALL);
      p.add = p.add.slice();
      p.rem = p.rem.slice();
      p.mod = p.mod.slice();
      if (p.source) p.source = p.source.slice();
      return p.materialize(ALL | SOURCE);
    };
  
    /**
     * Returns a pulse that adds all tuples from a backing source. This is
     * useful for cases where operators are added to a dataflow after an
     * upstream data pipeline has already been processed, ensuring that
     * new operators can observe all tuples within a stream.
     * @return {Pulse} - A pulse instance with all source tuples included
     *   in the add array. If the current pulse already has all source
     *   tuples in its add array, it is returned directly. If the current
     *   pulse does not have a backing source, it is returned directly.
     */
    prototype$3.addAll = function() {
      var p = this;
      if (!this.source || this.source.length === this.add.length) {
        return p;
      } else {
        p = new Pulse(this.dataflow).init(this);
        p.add = p.source;
        return p;
      }
    };
  
    /**
     * Initialize this pulse based on the values of another pulse. This method
     * is used internally by {@link fork} to initialize a new forked tuple.
     * The dataflow, time stamp and field modification values are copied over.
     * By default, new empty ADD, REM and MOD arrays are created.
     * @param {Pulse} src - The source pulse to copy from.
     * @param {number} flags - Integer of boolean flags indicating which (if any)
     *   tuple arrays should be copied to the new pulse. The supported flag values
     *   are ADD, REM and MOD. Array references are copied directly: new array
     *   instances are not created. By default, source data arrays are copied
     *   to the new pulse. Use the NO_SOURCE flag to enforce a null source.
     * @return {Pulse} - Returns this Pulse instance.
     */
    prototype$3.init = function(src, flags) {
      var p = this;
      p.stamp = src.stamp;
      p.encode = src.encode;
  
      if (src.fields && !(flags & NO_FIELDS)) {
        p.fields = src.fields;
      }
  
      if (flags & ADD) {
        p.addF = src.addF;
        p.add = src.add;
      } else {
        p.addF = null;
        p.add = [];
      }
  
      if (flags & REM) {
        p.remF = src.remF;
        p.rem = src.rem;
      } else {
        p.remF = null;
        p.rem = [];
      }
  
      if (flags & MOD) {
        p.modF = src.modF;
        p.mod = src.mod;
      } else {
        p.modF = null;
        p.mod = [];
      }
  
      if (flags & NO_SOURCE) {
        p.srcF = null;
        p.source = null;
      } else {
        p.srcF = src.srcF;
        p.source = src.source;
      }
  
      return p;
    };
  
    /**
     * Schedules a function to run after pulse propagation completes.
     * @param {function} func - The function to run.
     */
    prototype$3.runAfter = function(func) {
      this.dataflow.runAfter(func);
    };
  
    /**
     * Indicates if tuples have been added, removed or modified.
     * @param {number} [flags] - The tuple types (ADD, REM or MOD) to query.
     *   Defaults to ALL, returning true if any tuple type has changed.
     * @return {boolean} - Returns true if one or more queried tuple types have
     *   changed, false otherwise.
     */
    prototype$3.changed = function(flags) {
      var f = flags || ALL;
      return ((f & ADD) && this.add.length)
          || ((f & REM) && this.rem.length)
          || ((f & MOD) && this.mod.length);
    };
  
    /**
     * Forces a "reflow" of tuple values, such that all tuples in the backing
     * source are added to the MOD set, unless already present in the ADD set.
     * @param {boolean} [fork=false] - If true, returns a forked copy of this
     *   pulse, and invokes reflow on that derived pulse.
     * @return {Pulse} - The reflowed pulse instance.
     */
    prototype$3.reflow = function(fork) {
      if (fork) return this.fork(ALL).reflow();
  
      var len = this.add.length,
          src = this.source && this.source.length;
      if (src && src !== len) {
        this.mod = this.source;
        if (len) this.filter(MOD, filter(this, ADD));
      }
      return this;
    };
  
    /**
     * Marks one or more data field names as modified to assist dependency
     * tracking and incremental processing by transform operators.
     * @param {string|Array<string>} _ - The field(s) to mark as modified.
     * @return {Pulse} - This pulse instance.
     */
    prototype$3.modifies = function(_) {
      var fields = array(_),
          hash = this.fields || (this.fields = {});
      fields.forEach(function(f) { hash[f] = true; });
      return this;
    };
  
    /**
     * Checks if one or more data fields have been modified during this pulse
     * propagation timestamp.
     * @param {string|Array<string>} _ - The field(s) to check for modified.
     * @return {boolean} - Returns true if any of the provided fields has been
     *   marked as modified, false otherwise.
     */
    prototype$3.modified = function(_) {
      var fields = this.fields;
      return !(this.mod.length && fields) ? false
        : !arguments.length ? !!fields
        : isArray(_) ? _.some(function(f) { return fields[f]; })
        : fields[_];
    };
  
    /**
     * Adds a filter function to one more tuple sets. Filters are applied to
     * backing tuple arrays, to determine the actual set of tuples considered
     * added, removed or modified. They can be used to delay materialization of
     * a tuple set in order to avoid expensive array copies. In addition, the
     * filter functions can serve as value transformers: unlike standard predicate
     * function (which return boolean values), Pulse filters should return the
     * actual tuple value to process. If a tuple set is already filtered, the
     * new filter function will be appended into a conjuntive ('and') query.
     * @param {number} flags - Flags indicating the tuple set(s) to filter.
     * @param {function(*):object} filter - Filter function that will be applied
     *   to the tuple set array, and should return a data tuple if the value
     *   should be included in the tuple set, and falsy (or null) otherwise.
     * @return {Pulse} - Returns this pulse instance.
     */
    prototype$3.filter = function(flags, filter) {
      var p = this;
      if (flags & ADD) p.addF = addFilter(p.addF, filter);
      if (flags & REM) p.remF = addFilter(p.remF, filter);
      if (flags & MOD) p.modF = addFilter(p.modF, filter);
      if (flags & SOURCE) p.srcF = addFilter(p.srcF, filter);
      return p;
    };
  
    function addFilter(a, b) {
      return a ? function(t,i) { return a(t,i) && b(t,i); } : b;
    }
  
    /**
     * Materialize one or more tuple sets in this pulse. If the tuple set(s) have
     * a registered filter function, it will be applied and the tuple set(s) will
     * be replaced with materialized tuple arrays.
     * @param {number} flags - Flags indicating the tuple set(s) to materialize.
     * @return {Pulse} - Returns this pulse instance.
     */
    prototype$3.materialize = function(flags) {
      flags = flags || ALL;
      var p = this;
      if ((flags & ADD) && p.addF) {
        p.add = materialize(p.add, p.addF);
        p.addF = null;
      }
      if ((flags & REM) && p.remF) {
        p.rem = materialize(p.rem, p.remF);
        p.remF = null;
      }
      if ((flags & MOD) && p.modF) {
        p.mod = materialize(p.mod, p.modF);
        p.modF = null;
      }
      if ((flags & SOURCE) && p.srcF) {
        p.source = p.source.filter(p.srcF);
        p.srcF = null;
      }
      return p;
    };
  
    function materialize(data, filter) {
      var out = [];
      visitArray(data, filter, function(_) { out.push(_); });
      return out;
    }
  
    function filter(pulse, flags) {
      var map = {};
      pulse.visit(flags, function(t) { map[tupleid(t)] = 1; });
      return function(t) { return map[tupleid(t)] ? null : t; };
    }
  
    /**
     * Visit one or more tuple sets in this pulse.
     * @param {number} flags - Flags indicating the tuple set(s) to visit.
     *   Legal values are ADD, REM, MOD and SOURCE (if a backing data source
     *   has been set).
     * @param {function(object):*} - Visitor function invoked per-tuple.
     * @return {Pulse} - Returns this pulse instance.
     */
    prototype$3.visit = function(flags, visitor) {
      var p = this, v = visitor, src, sum;
  
      if (flags & SOURCE) {
        visitArray(p.source, p.srcF, v);
        return p;
      }
  
      if (flags & ADD) visitArray(p.add, p.addF, v);
      if (flags & REM) visitArray(p.rem, p.remF, v);
      if (flags & MOD) visitArray(p.mod, p.modF, v);
  
      if ((flags & REFLOW) && (src = p.source)) {
        sum = p.add.length + p.mod.length;
        if (sum === src.length) ; else if (sum) {
          visitArray(src, filter(p, ADD_MOD), v);
        } else {
          // if no add/rem/mod tuples, visit source
          visitArray(src, p.srcF, v);
        }
      }
  
      return p;
    };
  
    /**
     * Represents a set of multiple pulses. Used as input for operators
     * that accept multiple pulses at a time. Contained pulses are
     * accessible via the public "pulses" array property. This pulse doe
     * not carry added, removed or modified tuples directly. However,
     * the visit method can be used to traverse all such tuples contained
     * in sub-pulses with a timestamp matching this parent multi-pulse.
     * @constructor
     * @param {Dataflow} dataflow - The backing dataflow instance.
     * @param {number} stamp - The timestamp.
     * @param {Array<Pulse>} pulses - The sub-pulses for this multi-pulse.
     */
    function MultiPulse(dataflow, stamp, pulses, encode) {
      var p = this,
          c = 0,
          pulse, hash, i, n, f;
  
      this.dataflow = dataflow;
      this.stamp = stamp;
      this.fields = null;
      this.encode = encode || null;
      this.pulses = pulses;
  
      for (i=0, n=pulses.length; i<n; ++i) {
        pulse = pulses[i];
        if (pulse.stamp !== stamp) continue;
  
        if (pulse.fields) {
          hash = p.fields || (p.fields = {});
          for (f in pulse.fields) { hash[f] = 1; }
        }
  
        if (pulse.changed(p.ADD)) c |= p.ADD;
        if (pulse.changed(p.REM)) c |= p.REM;
        if (pulse.changed(p.MOD)) c |= p.MOD;
      }
  
      this.changes = c;
    }
  
    var prototype$4 = inherits(MultiPulse, Pulse);
  
    /**
     * Creates a new pulse based on the values of this pulse.
     * The dataflow, time stamp and field modification values are copied over.
     * @return {Pulse}
     */
    prototype$4.fork = function(flags) {
      var p = new Pulse(this.dataflow).init(this, flags & this.NO_FIELDS);
      if (flags !== undefined) {
        if (flags & p.ADD) {
          this.visit(p.ADD, function(t) { return p.add.push(t); });
        }
        if (flags & p.REM) {
          this.visit(p.REM, function(t) { return p.rem.push(t); });
        }
        if (flags & p.MOD) {
          this.visit(p.MOD, function(t) { return p.mod.push(t); });
        }
      }
      return p;
    };
  
    prototype$4.changed = function(flags) {
      return this.changes & flags;
    };
  
    prototype$4.modified = function(_) {
      var p = this, fields = p.fields;
      return !(fields && (p.changes & p.MOD)) ? 0
        : isArray(_) ? _.some(function(f) { return fields[f]; })
        : fields[_];
    };
  
    prototype$4.filter = function() {
      error('MultiPulse does not support filtering.');
    };
  
    prototype$4.materialize = function() {
      error('MultiPulse does not support materialization.');
    };
  
    prototype$4.visit = function(flags, visitor) {
      var p = this,
          pulses = p.pulses,
          n = pulses.length,
          i = 0;
  
      if (flags & p.SOURCE) {
        for (; i<n; ++i) {
          pulses[i].visit(flags, visitor);
        }
      } else {
        for (; i<n; ++i) {
          if (pulses[i].stamp === p.stamp) {
            pulses[i].visit(flags, visitor);
          }
        }
      }
  
      return p;
    };
  
    /**
     * Evaluates the dataflow and returns a Promise that resolves when pulse
     * propagation completes. This method will increment the current timestamp
     * and process all updated, pulsed and touched operators. When invoked for
     * the first time, all registered operators will be processed. This method
     * should not be invoked by third-party clients, use {@link runAsync} or
     * {@link run} instead.
     * @param {string} [encode] - The name of an encoding set to invoke during
     *   propagation. This value is added to generated Pulse instances;
     *   operators can then respond to (or ignore) this setting as appropriate.
     *   This parameter can be used in conjunction with the Encode transform in
     *   the vega-encode package.
     * @param {function} [prerun] - An optional callback function to invoke
     *   immediately before dataflow evaluation commences.
     * @param {function} [postrun] - An optional callback function to invoke
     *   after dataflow evaluation completes. The callback will be invoked
     *   after those registered via {@link runAfter}.
     * @return {Promise} - A promise that resolves to this dataflow after
     *   evaluation completes.
     */
    async function evaluate(encode, prerun, postrun) {
      const df = this,
            level = df.logLevel();
  
      // if the pulse value is set, this is a re-entrant call
      if (df._pulse) return reentrant(df);
  
      // wait for pending datasets to load
      if (df._pending) {
        await df._pending;
      }
  
      // invoke prerun function, if provided
      if (prerun) await asyncCallback(df, prerun);
  
      // exit early if there are no updates
      if (!df._touched.length) {
        df.info('Dataflow invoked, but nothing to do.');
        return df;
      }
  
      // increment timestamp clock
      let stamp = ++df._clock,
          count = 0, op, next, dt, error;
  
      // set the current pulse
      df._pulse = new Pulse(df, stamp, encode);
  
      if (level >= Info) {
        dt = Date.now();
        df.debug('-- START PROPAGATION (' + stamp + ') -----');
      }
  
      // initialize priority queue, reset touched operators
      df._touched.forEach(function(op) { df._enqueue(op, true); });
      df._touched = UniqueList(id);
  
      try {
        while (df._heap.size() > 0) {
          // dequeue operator with highest priority
          op = df._heap.pop();
  
          // re-queue if rank changed
          if (op.rank !== op.qrank) { df._enqueue(op, true); continue; }
  
          // otherwise, evaluate the operator
          next = op.run(df._getPulse(op, encode));
  
          // await if operator returned a promise
          if (next.then) {
            next = await next;
          }
  
          if (level >= Debug) {
            df.debug(op.id, next === StopPropagation ? 'STOP' : next, op);
          }
  
          // propagate evaluation, enqueue dependent operators
          if (next !== StopPropagation) {
            df._pulse = next;
            if (op._targets) op._targets.forEach(op => df._enqueue(op));
          }
  
          // increment visit counter
          ++count;
        }
      } catch (err) {
        error = err;
      }
  
      // reset pulse map
      df._pulses = {};
      df._pulse = null;
  
      if (level >= Info) {
        dt = Date.now() - dt;
        df.info('> Pulse ' + stamp + ': ' + count + ' operators; ' + dt + 'ms');
      }
  
      if (error) {
        df._postrun = [];
        df.error(error);
      }
  
      // invoke callbacks queued via runAfter
      if (df._postrun.length) {
        const pr = df._postrun.sort((a, b) => b.priority - a.priority);
        df._postrun = [];
        for (let i=0; i<pr.length; ++i) {
          await asyncCallback(df, pr[i].callback);
        }
      }
  
      // invoke postrun function, if provided
      if (postrun) await asyncCallback(df, postrun);
  
      return df;
    }
  
    /**
     * Queues dataflow evaluation to run once any other queued evaluations have
     * completed and returns a Promise that resolves when the queued pulse
     * propagation completes. If provided, a callback function will be invoked
     * immediately before evaluation commences. This method will ensure a
     * separate evaluation is invoked for each time it is called.
     * @param {string} [encode] - The name of an encoding set to invoke during
     *   propagation. This value is added to generated Pulse instances;
     *   operators can then respond to (or ignore) this setting as appropriate.
     *   This parameter can be used in conjunction with the Encode transform in
     *   the vega-encode package.
     * @param {function} [prerun] - An optional callback function to invoke
     *   immediately before dataflow evaluation commences.
     * @param {function} [postrun] - An optional callback function to invoke
     *   after dataflow evaluation completes. The callback will be invoked
     *   after those registered via {@link runAfter}.
     * @return {Promise} - A promise that resolves to this dataflow after
     *   evaluation completes.
     */
    async function runAsync(encode, prerun, postrun) {
      // await previously queued functions
      while (this._running) await this._running;
  
      // run dataflow, manage running promise
      const clear = () => this._running = null;
      (this._running = this.evaluate(encode, prerun, postrun))
        .then(clear, clear);
  
      return this._running;
    }
  
    /**
     * Requests dataflow evaluation and the immediately returns this dataflow
     * instance. If there are pending data loading or other asynchronous
     * operations, the dataflow will evaluate asynchronously after this method
     * has been invoked. To track when dataflow evaluation completes, use the
     * {@link runAsync} method instead. This method will raise an error if
     * invoked while the dataflow is already in the midst of evaluation.
     * @param {string} [encode] - The name of an encoding set to invoke during
     *   propagation. This value is added to generated Pulse instances;
     *   operators can then respond to (or ignore) this setting as appropriate.
     *   This parameter can be used in conjunction with the Encode transform in
     *   the vega-encode module.
     * @param {function} [prerun] - An optional callback function to invoke
     *   immediately before dataflow evaluation commences.
     * @param {function} [postrun] - An optional callback function to invoke
     *   after dataflow evaluation completes. The callback will be invoked
     *   after those registered via {@link runAfter}.
     * @return {Dataflow} - This dataflow instance.
     */
    function run(encode, prerun, postrun) {
      return this._pulse ? reentrant(this)
        : (this.evaluate(encode, prerun, postrun), this);
    }
  
    /**
     * Schedules a callback function to be invoked after the current pulse
     * propagation completes. If no propagation is currently occurring,
     * the function is invoked immediately. Callbacks scheduled via runAfter
     * are invoked immediately upon completion of the current cycle, before
     * any request queued via runAsync. This method is primarily intended for
     * internal use. Third-party callers using runAfter to schedule a callback
     * that invokes {@link run} or {@link runAsync} should not use this method,
     * but instead use {@link runAsync} with prerun or postrun arguments.
     * @param {function(Dataflow)} callback - The callback function to run.
     *   The callback will be invoked with this Dataflow instance as its
     *   sole argument.
     * @param {boolean} enqueue - A boolean flag indicating that the
     *   callback should be queued up to run after the next propagation
     *   cycle, suppressing immediate invocation when propagation is not
     *   currently occurring.
     * @param {number} [priority] - A priority value used to sort registered
     *   callbacks to determine execution order. This argument is intended
     *   for internal Vega use only.
     */
    function runAfter(callback, enqueue, priority) {
      if (this._pulse || enqueue) {
        // pulse propagation is currently running, queue to run after
        this._postrun.push({
          priority: priority || 0,
          callback: callback
        });
      } else {
        // pulse propagation already complete, invoke immediately
        try { callback(this); } catch (err) { this.error(err); }
      }
    }
  
    /**
     * Raise an error for re-entrant dataflow evaluation.
     */
    function reentrant(df) {
      df.error('Dataflow already running. Use runAsync() to chain invocations.');
      return df;
    }
  
    /**
     * Enqueue an operator into the priority queue for evaluation. The operator
     * will be enqueued if it has no registered pulse for the current cycle, or if
     * the force argument is true. Upon enqueue, this method also sets the
     * operator's qrank to the current rank value.
     * @param {Operator} op - The operator to enqueue.
     * @param {boolean} [force] - A flag indicating if the operator should be
     *   forceably added to the queue, even if it has already been previously
     *   enqueued during the current pulse propagation. This is useful when the
     *   dataflow graph is dynamically modified and the operator rank changes.
     */
    function enqueue(op, force) {
      var p = !this._pulses[op.id];
      if (p) this._pulses[op.id] = this._pulse;
      if (p || force) {
        op.qrank = op.rank;
        this._heap.push(op);
      }
    }
  
    /**
     * Provide a correct pulse for evaluating an operator. If the operator has an
     * explicit source operator, we will try to pull the pulse(s) from it.
     * If there is an array of source operators, we build a multi-pulse.
     * Otherwise, we return a current pulse with correct source data.
     * If the pulse is the pulse map has an explicit target set, we use that.
     * Else if the pulse on the upstream source operator is current, we use that.
     * Else we use the pulse from the pulse map, but copy the source tuple array.
     * @param {Operator} op - The operator for which to get an input pulse.
     * @param {string} [encode] - An (optional) encoding set name with which to
     *   annotate the returned pulse. See {@link run} for more information.
     */
    function getPulse(op, encode) {
      var s = op.source,
          stamp = this._clock,
          p;
  
      if (s && isArray(s)) {
        p = s.map(function(_) { return _.pulse; });
        return new MultiPulse(this, stamp, p, encode);
      }
  
      p = this._pulses[op.id];
      if (s) {
        s = s.pulse;
        if (!s || s === StopPropagation) {
          p.source = [];
        } else if (s.stamp === stamp && p.target !== op) {
          p = s;
        } else {
          p.source = s.source;
        }
      }
  
      return p;
    }
  
    var NO_OPT = {skip: false, force: false};
  
    /**
     * Touches an operator, scheduling it to be evaluated. If invoked outside of
     * a pulse propagation, the operator will be evaluated the next time this
     * dataflow is run. If invoked in the midst of pulse propagation, the operator
     * will be queued for evaluation if and only if the operator has not yet been
     * evaluated on the current propagation timestamp.
     * @param {Operator} op - The operator to touch.
     * @param {object} [options] - Additional options hash.
     * @param {boolean} [options.skip] - If true, the operator will
     *   be skipped: it will not be evaluated, but its dependents will be.
     * @return {Dataflow}
     */
    function touch(op, options) {
      var opt = options || NO_OPT;
      if (this._pulse) {
        // if in midst of propagation, add to priority queue
        this._enqueue(op);
      } else {
        // otherwise, queue for next propagation
        this._touched.add(op);
      }
      if (opt.skip) op.skip(true);
      return this;
    }
  
    /**
     * Updates the value of the given operator.
     * @param {Operator} op - The operator to update.
     * @param {*} value - The value to set.
     * @param {object} [options] - Additional options hash.
     * @param {boolean} [options.force] - If true, the operator will
     *   be re-evaluated even if its value has not changed.
     * @param {boolean} [options.skip] - If true, the operator will
     *   be skipped: it will not be evaluated, but its dependents will be.
     * @return {Dataflow}
     */
    function update(op, value, options) {
      var opt = options || NO_OPT;
      if (op.set(value) || opt.force) {
        this.touch(op, opt);
      }
      return this;
    }
  
    /**
     * Pulses an operator with a changeset of tuples. If invoked outside of
     * a pulse propagation, the pulse will be applied the next time this
     * dataflow is run. If invoked in the midst of pulse propagation, the pulse
     * will be added to the set of active pulses and will be applied if and
     * only if the target operator has not yet been evaluated on the current
     * propagation timestamp.
     * @param {Operator} op - The operator to pulse.
     * @param {ChangeSet} value - The tuple changeset to apply.
     * @param {object} [options] - Additional options hash.
     * @param {boolean} [options.skip] - If true, the operator will
     *   be skipped: it will not be evaluated, but its dependents will be.
     * @return {Dataflow}
     */
    function pulse(op, changeset, options) {
      this.touch(op, options || NO_OPT);
  
      var p = new Pulse(this, this._clock + (this._pulse ? 0 : 1)),
          t = op.pulse && op.pulse.source || [];
      p.target = op;
      this._pulses[op.id] = changeset.pulse(p, t);
  
      return this;
    }
  
    function Heap(cmp) {
      var nodes = [];
      return {
        size: () => nodes.length,
        peek: () => nodes[0],
        push: x => {
          nodes.push(x);
          return siftdown(nodes, 0, nodes.length - 1, cmp);
        },
        pop: () => {
          var last = nodes.pop(), item;
          if (nodes.length) {
            item = nodes[0];
            nodes[0] = last;
            siftup(nodes, 0, cmp);
          } else {
            item = last;
          }
          return item;
        }
      };
    }
  
    function siftdown(array, start, idx, cmp) {
      var item, parent, pidx;
  
      item = array[idx];
      while (idx > start) {
        pidx = (idx - 1) >> 1;
        parent = array[pidx];
        if (cmp(item, parent) < 0) {
          array[idx] = parent;
          idx = pidx;
          continue;
        }
        break;
      }
      return (array[idx] = item);
    }
  
    function siftup(array, idx, cmp) {
      var start = idx,
          end = array.length,
          item = array[idx],
          cidx = (idx << 1) + 1, ridx;
  
      while (cidx < end) {
        ridx = cidx + 1;
        if (ridx < end && cmp(array[cidx], array[ridx]) >= 0) {
          cidx = ridx;
        }
        array[idx] = array[cidx];
        idx = cidx;
        cidx = (idx << 1) + 1;
      }
      array[idx] = item;
      return siftdown(array, start, idx, cmp);
    }
  
    /**
     * A dataflow graph for reactive processing of data streams.
     * @constructor
     */
    function Dataflow() {
      this.logger(logger());
      this.logLevel(Error$1);
  
      this._clock = 0;
      this._rank = 0;
      try {
        this._loader = loader();
      } catch (e) {
        // do nothing if loader module is unavailable
      }
  
      this._touched = UniqueList(id);
      this._pulses = {};
      this._pulse = null;
  
      this._heap = Heap((a, b) => a.qrank - b.qrank);
      this._postrun = [];
    }
  
    var prototype$5 = Dataflow.prototype;
  
    /**
     * The current timestamp of this dataflow. This value reflects the
     * timestamp of the previous dataflow run. The dataflow is initialized
     * with a stamp value of 0. The initial run of the dataflow will have
     * a timestap of 1, and so on. This value will match the
     * {@link Pulse.stamp} property.
     * @return {number} - The current timestamp value.
     */
    prototype$5.stamp = function() {
      return this._clock;
    };
  
    /**
     * Gets or sets the loader instance to use for data file loading. A
     * loader object must provide a "load" method for loading files and a
     * "sanitize" method for checking URL/filename validity. Both methods
     * should accept a URI and options hash as arguments, and return a Promise
     * that resolves to the loaded file contents (load) or a hash containing
     * sanitized URI data with the sanitized url assigned to the "href" property
     * (sanitize).
     * @param {object} _ - The loader instance to use.
     * @return {object|Dataflow} - If no arguments are provided, returns
     *   the current loader instance. Otherwise returns this Dataflow instance.
     */
    prototype$5.loader = function(_) {
      if (arguments.length) {
        this._loader = _;
        return this;
      } else {
        return this._loader;
      }
    };
  
    /**
     * Empty entry threshold for garbage cleaning. Map data structures will
     * perform cleaning once the number of empty entries exceeds this value.
     */
    prototype$5.cleanThreshold = 1e4;
  
    // OPERATOR REGISTRATION
    prototype$5.add = add;
    prototype$5.connect = connect;
    prototype$5.rank = rank;
    prototype$5.rerank = rerank;
  
    // OPERATOR UPDATES
    prototype$5.pulse = pulse;
    prototype$5.touch = touch;
    prototype$5.update = update;
    prototype$5.changeset = changeset;
  
    // DATA LOADING
    prototype$5.ingest = ingest$1;
    prototype$5.parse  = parse$1;
    prototype$5.preload = preload;
    prototype$5.request = request;
  
    // EVENT HANDLING
    prototype$5.events = events;
    prototype$5.on = on;
  
    // PULSE PROPAGATION
    prototype$5.evaluate = evaluate;
    prototype$5.run = run;
    prototype$5.runAsync = runAsync;
    prototype$5.runAfter = runAfter;
    prototype$5._enqueue = enqueue;
    prototype$5._getPulse = getPulse;
  
    // LOGGING AND ERROR HANDLING
  
    function logMethod(method) {
      return function() {
        return this._log[method].apply(this, arguments);
      };
    }
  
    /**
     * Get or set the logger instance used to log messages. If no arguments are
     * provided, returns the current logger instance. Otherwise, sets the logger
     * and return this Dataflow instance. Provided loggers must support the full
     * API of logger objects generated by the vega-util logger method. Note that
     * by default the log level of the new logger will be used; use the logLevel
     * method to adjust the log level as needed.
     */
    prototype$5.logger = function(logger) {
      if (arguments.length) {
        this._log = logger;
        return this;
      } else {
        return this._log;
      }
    };
  
    /**
     * Logs an error message. By default, logged messages are written to console
     * output. The message will only be logged if the current log level is high
     * enough to permit error messages.
     */
    prototype$5.error = logMethod('error');
  
    /**
     * Logs a warning message. By default, logged messages are written to console
     * output. The message will only be logged if the current log level is high
     * enough to permit warning messages.
     */
    prototype$5.warn = logMethod('warn');
  
    /**
     * Logs a information message. By default, logged messages are written to
     * console output. The message will only be logged if the current log level is
     * high enough to permit information messages.
     */
    prototype$5.info = logMethod('info');
  
    /**
     * Logs a debug message. By default, logged messages are written to console
     * output. The message will only be logged if the current log level is high
     * enough to permit debug messages.
     */
    prototype$5.debug = logMethod('debug');
  
    /**
     * Get or set the current log level. If an argument is provided, it
     * will be used as the new log level.
     * @param {number} [level] - Should be one of None, Warn, Info
     * @return {number} - The current log level.
     */
    prototype$5.logLevel = logMethod('level');
  
    /**
     * Abstract class for operators that process data tuples.
     * Subclasses must provide a {@link transform} method for operator processing.
     * @constructor
     * @param {*} [init] - The initial value for this operator.
     * @param {object} [params] - The parameters for this operator.
     * @param {Operator} [source] - The operator from which to receive pulses.
     */
    function Transform(init, params) {
      Operator.call(this, init, null, params);
    }
  
    var prototype$6 = inherits(Transform, Operator);
  
    /**
     * Overrides {@link Operator.evaluate} for transform operators.
     * Internally, this method calls {@link evaluate} to perform processing.
     * If {@link evaluate} returns a falsy value, the input pulse is returned.
     * This method should NOT be overridden, instead overrride {@link evaluate}.
     * @param {Pulse} pulse - the current dataflow pulse.
     * @return the output pulse for this operator (or StopPropagation)
     */
    prototype$6.run = function(pulse) {
      if (pulse.stamp <= this.stamp) return pulse.StopPropagation;
  
      var rv;
      if (this.skip()) {
        this.skip(false);
      } else {
        rv = this.evaluate(pulse);
      }
      rv = rv || pulse;
  
      this.stamp = pulse.stamp;
  
      if (rv.then) {
        rv = rv.then(_ => this.pulse =_);
      } else if (rv !== pulse.StopPropagation) {
        this.pulse = rv;
      }
  
      return rv;
    };
  
    /**
     * Overrides {@link Operator.evaluate} for transform operators.
     * Marshalls parameter values and then invokes {@link transform}.
     * @param {Pulse} pulse - the current dataflow pulse.
     * @return {Pulse} The output pulse (or StopPropagation). A falsy return
         value (including undefined) will let the input pulse pass through.
     */
    prototype$6.evaluate = function(pulse) {
      var params = this.marshall(pulse.stamp),
          out = this.transform(params, pulse);
      params.clear();
      return out;
    };
  
    /**
     * Process incoming pulses.
     * Subclasses should override this method to implement transforms.
     * @param {Parameters} _ - The operator parameter values.
     * @param {Pulse} pulse - The current dataflow pulse.
     * @return {Pulse} The output pulse (or StopPropagation). A falsy return
     *   value (including undefined) will let the input pulse pass through.
     */
    prototype$6.transform = function() {};
  
    var transforms = {};
  
    function definition(type) {
      var t = transform(type);
      return t && t.Definition || null;
    }
  
    function transform(type) {
      type = type && type.toLowerCase();
      return transforms.hasOwnProperty(type) ? transforms[type] : null;
    }
  
    function multikey(f) {
      return function(x) {
        var n = f.length,
            i = 1,
            k = String(f[0](x));
  
        for (; i<n; ++i) {
          k += '|' + f[i](x);
        }
  
        return k;
      };
    }
  
    function groupkey(fields) {
      return !fields || !fields.length ? function() { return ''; }
        : fields.length === 1 ? fields[0]
        : multikey(fields);
    }
  
    function measureName(op, field, as) {
      return as || (op + (!field ? '' : '_' + field));
    }
  
    var AggregateOps = {
      'values': measure({
        name: 'values',
        init: 'cell.store = true;',
        set:  'cell.data.values()', idx: -1
      }),
      'count': measure({
        name: 'count',
        set:  'cell.num'
      }),
      '__count__': measure({
        name: 'count',
        set:  'this.missing + this.valid'
      }),
      'missing': measure({
        name: 'missing',
        set:  'this.missing'
      }),
      'valid': measure({
        name: 'valid',
        set:  'this.valid'
      }),
      'sum': measure({
        name: 'sum',
        init: 'this.sum = 0;',
        add:  'this.sum += +v;',
        rem:  'this.sum -= v;',
        set:  'this.sum'
      }),
      'mean': measure({
        name: 'mean',
        init: 'this.mean = 0;',
        add:  'var d = v - this.mean; this.mean += d / this.valid;',
        rem:  'var d = v - this.mean; this.mean -= this.valid ? d / this.valid : this.mean;',
        set:  'this.valid ? this.mean : undefined'
      }),
      'average': measure({
        name: 'average',
        set:  'this.valid ? this.mean : undefined',
        req:  ['mean'], idx: 1
      }),
      'variance': measure({
        name: 'variance',
        init: 'this.dev = 0;',
        add:  'this.dev += d * (v - this.mean);',
        rem:  'this.dev -= d * (v - this.mean);',
        set:  'this.valid > 1 ? this.dev / (this.valid-1) : undefined',
        req:  ['mean'], idx: 1
      }),
      'variancep': measure({
        name: 'variancep',
        set:  'this.valid > 1 ? this.dev / this.valid : undefined',
        req:  ['variance'], idx: 2
      }),
      'stdev': measure({
        name: 'stdev',
        set:  'this.valid > 1 ? Math.sqrt(this.dev / (this.valid-1)) : undefined',
        req:  ['variance'], idx: 2
      }),
      'stdevp': measure({
        name: 'stdevp',
        set:  'this.valid > 1 ? Math.sqrt(this.dev / this.valid) : undefined',
        req:  ['variance'], idx: 2
      }),
      'stderr': measure({
        name: 'stderr',
        set:  'this.valid > 1 ? Math.sqrt(this.dev / (this.valid * (this.valid-1))) : undefined',
        req:  ['variance'], idx: 2
      }),
      'distinct': measure({
        name: 'distinct',
        set:  'cell.data.distinct(this.get)',
        req:  ['values'], idx: 3
      }),
      'ci0': measure({
        name: 'ci0',
        set:  'cell.data.ci0(this.get)',
        req:  ['values'], idx: 3
      }),
      'ci1': measure({
        name: 'ci1',
        set:  'cell.data.ci1(this.get)',
        req:  ['values'], idx: 3
      }),
      'median': measure({
        name: 'median',
        set:  'cell.data.q2(this.get)',
        req:  ['values'], idx: 3
      }),
      'q1': measure({
        name: 'q1',
        set:  'cell.data.q1(this.get)',
        req:  ['values'], idx: 3
      }),
      'q3': measure({
        name: 'q3',
        set:  'cell.data.q3(this.get)',
        req:  ['values'], idx: 3
      }),
      'argmin': measure({
        name: 'argmin',
        init: 'this.argmin = undefined;',
        add:  'if (v < this.min) this.argmin = t;',
        rem:  'if (v <= this.min) this.argmin = undefined;',
        set:  'this.argmin || cell.data.argmin(this.get)',
        req:  ['min'], str: ['values'], idx: 3
      }),
      'argmax': measure({
        name: 'argmax',
        init: 'this.argmax = undefined;',
        add:  'if (v > this.max) this.argmax = t;',
        rem:  'if (v >= this.max) this.argmax = undefined;',
        set:  'this.argmax || cell.data.argmax(this.get)',
        req:  ['max'], str: ['values'], idx: 3
      }),
      'min': measure({
        name: 'min',
        init: 'this.min = undefined;',
        add:  'if (v < this.min || this.min === undefined) this.min = v;',
        rem:  'if (v <= this.min) this.min = NaN;',
        set:  'this.min = (isNaN(this.min) ? cell.data.min(this.get) : this.min)',
        str:  ['values'], idx: 4
      }),
      'max': measure({
        name: 'max',
        init: 'this.max = undefined;',
        add:  'if (v > this.max || this.max === undefined) this.max = v;',
        rem:  'if (v >= this.max) this.max = NaN;',
        set:  'this.max = (isNaN(this.max) ? cell.data.max(this.get) : this.max)',
        str:  ['values'], idx: 4
      })
    };
  
    var ValidAggregateOps = Object.keys(AggregateOps);
  
    function createMeasure(op, name) {
      return AggregateOps[op](name);
    }
  
    function measure(base) {
      return function(out) {
        var m = extend({init:'', add:'', rem:'', idx:0}, base);
        m.out = out || base.name;
        return m;
      };
    }
  
    function compareIndex(a, b) {
      return a.idx - b.idx;
    }
  
    function resolve(agg, stream) {
      function collect(m, a) {
        function helper(r) { if (!m[r]) collect(m, m[r] = AggregateOps[r]()); }
        if (a.req) a.req.forEach(helper);
        if (stream && a.str) a.str.forEach(helper);
        return m;
      }
      var map = agg.reduce(
        collect,
        agg.reduce(function(m, a) {
          m[a.name] = a;
          return m;
        }, {})
      );
      var values = [], key;
      for (key in map) values.push(map[key]);
      return values.sort(compareIndex);
    }
  
    function compileMeasures(agg, field) {
      var get = field || identity,
          all = resolve(agg, true), // assume streaming removes may occur
          init = 'var cell = this.cell; this.valid = 0; this.missing = 0;',
          ctr = 'this.cell = cell; this.init();',
          add = 'if(v==null){++this.missing; return;} if(v!==v) return; ++this.valid;',
          rem = 'if(v==null){--this.missing; return;} if(v!==v) return; --this.valid;',
          set = 'var cell = this.cell;';
  
      all.forEach(function(a) {
        init += a.init;
        add += a.add;
        rem += a.rem;
      });
      agg.slice().sort(compareIndex).forEach(function(a) {
        set += 't[\'' + a.out + '\']=' + a.set + ';';
      });
      set += 'return t;';
  
      ctr = Function('cell', ctr);
      ctr.prototype.init = Function(init);
      ctr.prototype.add = Function('v', 't', add);
      ctr.prototype.rem = Function('v', 't', rem);
      ctr.prototype.set = Function('t', set);
      ctr.prototype.get = get;
      ctr.fields = agg.map(function(_) { return _.out; });
      return ctr;
    }
  
    function bin(_) {
      // determine range
      var maxb = _.maxbins || 20,
          base = _.base || 10,
          logb = Math.log(base),
          div  = _.divide || [5, 2],
          min  = _.extent[0],
          max  = _.extent[1],
          span = (max - min) || Math.abs(min) || 1,
          step, level, minstep, precision, v, i, n, eps;
  
      if (_.step) {
        // if step size is explicitly given, use that
        step = _.step;
      } else if (_.steps) {
        // if provided, limit choice to acceptable step sizes
        v = span / maxb;
        for (i=0, n=_.steps.length; i < n && _.steps[i] < v; ++i);
        step = _.steps[Math.max(0, i-1)];
      } else {
        // else use span to determine step size
        level = Math.ceil(Math.log(maxb) / logb);
        minstep = _.minstep || 0;
        step = Math.max(
          minstep,
          Math.pow(base, Math.round(Math.log(span) / logb) - level)
        );
  
        // increase step size if too many bins
        while (Math.ceil(span/step) > maxb) { step *= base; }
  
        // decrease step size if allowed
        for (i=0, n=div.length; i<n; ++i) {
          v = step / div[i];
          if (v >= minstep && span / v <= maxb) step = v;
        }
      }
  
      // update precision, min and max
      v = Math.log(step);
      precision = v >= 0 ? 0 : ~~(-v / logb) + 1;
      eps = Math.pow(base, -precision - 1);
      if (_.nice || _.nice === undefined) {
        v = Math.floor(min / step + eps) * step;
        min = min < v ? v - step : v;
        max = Math.ceil(max / step) * step;
      }
  
      return {
        start: min,
        stop:  max === min ? min + step : max,
        step:  step
      };
    }
  
    function* numbers(values, valueof) {
      if (valueof === undefined) {
        for (let value of values) {
          if (value != null && (value = +value) >= value) {
            yield value;
          }
        }
      } else {
        let index = -1;
        for (let value of values) {
          if ((value = valueof(value, ++index, values)) != null && (value = +value) >= value) {
            yield value;
          }
        }
      }
    }
  
    exports.random = Math.random;
  
    function setRandom(r) {
      exports.random = r;
    }
  
    function bootstrapCI(array, samples, alpha, f) {
      if (!array.length) return [undefined, undefined];
  
      var values = Float64Array.from(numbers(array, f)),
          n = values.length,
          m = samples,
          a, i, j, mu;
  
      for (j=0, mu=Array(m); j<m; ++j) {
        for (a=0, i=0; i<n; ++i) {
          a += values[~~(exports.random() * n)];
        }
        mu[j] = a / n;
      }
  
      mu.sort(d3Array.ascending);
  
      return [
        d3Array.quantile(mu, alpha/2),
        d3Array.quantile(mu, 1-(alpha/2))
      ];
    }
  
    function quartiles(array, f) {
      var values = Float64Array.from(numbers(array, f));
  
      // don't depend on return value from typed array sort call
      // protects against undefined sort results in Safari (vega/vega-lite#4964)
      values.sort(d3Array.ascending);
  
      return [
        d3Array.quantile(values, 0.25),
        d3Array.quantile(values, 0.50),
        d3Array.quantile(values, 0.75)
      ];
    }
  
    function lcg(seed) {
      // Random numbers using a Linear Congruential Generator with seed value
      // Uses glibc values from https://en.wikipedia.org/wiki/Linear_congruential_generator
      return function() {
        seed = (1103515245 * seed + 12345) % 2147483647;
        return seed / 2147483647;
      };
    }
  
    function integer(min, max) {
      if (max == null) {
        max = min;
        min = 0;
      }
  
      var dist = {},
          a, b, d;
  
      dist.min = function(_) {
        if (arguments.length) {
          a = _ || 0;
          d = b - a;
          return dist;
        } else {
          return a;
        }
      };
  
      dist.max = function(_) {
        if (arguments.length) {
          b = _ || 0;
          d = b - a;
          return dist;
        } else {
          return b;
        }
      };
  
      dist.sample = function() {
        return a + Math.floor(d * exports.random());
      };
  
      dist.pdf = function(x) {
        return (x === Math.floor(x) && x >= a && x < b) ? 1 / d : 0;
      };
  
      dist.cdf = function(x) {
        var v = Math.floor(x);
        return v < a ? 0 : v >= b ? 1 : (v - a + 1) / d;
      };
  
      dist.icdf = function(p) {
        return (p >= 0 && p <= 1) ? a - 1 + Math.floor(p * d) : NaN;
      };
  
      return dist.min(min).max(max);
    }
  
    function randomNormal(mean, stdev) {
      var mu,
          sigma,
          next = NaN,
          dist = {};
  
      dist.mean = function(_) {
        if (arguments.length) {
          mu = _ || 0;
          next = NaN;
          return dist;
        } else {
          return mu;
        }
      };
  
      dist.stdev = function(_) {
        if (arguments.length) {
          sigma = _ == null ? 1 : _;
          next = NaN;
          return dist;
        } else {
          return sigma;
        }
      };
  
      dist.sample = function() {
        var x = 0, y = 0, rds, c;
        if (next === next) {
          x = next;
          next = NaN;
          return x;
        }
        do {
          x = exports.random() * 2 - 1;
          y = exports.random() * 2 - 1;
          rds = x * x + y * y;
        } while (rds === 0 || rds > 1);
        c = Math.sqrt(-2 * Math.log(rds) / rds); // Box-Muller transform
        next = mu + y * c * sigma;
        return mu + x * c * sigma;
      };
  
      dist.pdf = function(x) {
        var exp = Math.exp(Math.pow(x-mu, 2) / (-2 * Math.pow(sigma, 2)));
        return (1 / (sigma * Math.sqrt(2*Math.PI))) * exp;
      };
  
      // Approximation from West (2009)
      // Better Approximations to Cumulative Normal Functions
      dist.cdf = function(x) {
        var cd,
            z = (x - mu) / sigma,
            Z = Math.abs(z);
        if (Z > 37) {
          cd = 0;
        } else {
          var sum, exp = Math.exp(-Z*Z/2);
          if (Z < 7.07106781186547) {
            sum = 3.52624965998911e-02 * Z + 0.700383064443688;
            sum = sum * Z + 6.37396220353165;
            sum = sum * Z + 33.912866078383;
            sum = sum * Z + 112.079291497871;
            sum = sum * Z + 221.213596169931;
            sum = sum * Z + 220.206867912376;
            cd = exp * sum;
            sum = 8.83883476483184e-02 * Z + 1.75566716318264;
            sum = sum * Z + 16.064177579207;
            sum = sum * Z + 86.7807322029461;
            sum = sum * Z + 296.564248779674;
            sum = sum * Z + 637.333633378831;
            sum = sum * Z + 793.826512519948;
            sum = sum * Z + 440.413735824752;
            cd = cd / sum;
          } else {
            sum = Z + 0.65;
            sum = Z + 4 / sum;
            sum = Z + 3 / sum;
            sum = Z + 2 / sum;
            sum = Z + 1 / sum;
            cd = exp / sum / 2.506628274631;
          }
        }
        return z > 0 ? 1 - cd : cd;
      };
  
      // Approximation of Probit function using inverse error function.
      dist.icdf = function(p) {
        if (p <= 0 || p >= 1) return NaN;
        var x = 2*p - 1,
            v = (8 * (Math.PI - 3)) / (3 * Math.PI * (4-Math.PI)),
            a = (2 / (Math.PI*v)) + (Math.log(1 - Math.pow(x,2)) / 2),
            b = Math.log(1 - (x*x)) / v,
            s = (x > 0 ? 1 : -1) * Math.sqrt(Math.sqrt((a*a) - b) - a);
        return mu + sigma * Math.SQRT2 * s;
      };
  
      return dist.mean(mean).stdev(stdev);
    }
  
    // TODO: support for additional kernels?
    function randomKDE(support, bandwidth) {
      var kernel = randomNormal(),
          dist = {},
          n = 0;
  
      dist.data = function(_) {
        if (arguments.length) {
          support = _;
          n = _ ? _.length : 0;
          return dist.bandwidth(bandwidth);
        } else {
          return support;
        }
      };
  
      dist.bandwidth = function(_) {
        if (!arguments.length) return bandwidth;
        bandwidth = _;
        if (!bandwidth && support) bandwidth = estimateBandwidth(support);
        return dist;
      };
  
      dist.sample = function() {
        return support[~~(exports.random() * n)] + bandwidth * kernel.sample();
      };
  
      dist.pdf = function(x) {
        for (var y=0, i=0; i<n; ++i) {
          y += kernel.pdf((x - support[i]) / bandwidth);
        }
        return y / bandwidth / n;
      };
  
      dist.cdf = function(x) {
        for (var y=0, i=0; i<n; ++i) {
          y += kernel.cdf((x - support[i]) / bandwidth);
        }
        return y / n;
      };
  
      dist.icdf = function() {
        throw Error('KDE icdf not supported.');
      };
  
      return dist.data(support);
    }
  
    // Scott, D. W. (1992) Multivariate Density Estimation:
    // Theory, Practice, and Visualization. Wiley.
    function estimateBandwidth(array) {
      var n = array.length,
          q = quartiles(array),
          h = (q[2] - q[0]) / 1.34;
      return 1.06 * Math.min(Math.sqrt(d3Array.variance(array)), h) * Math.pow(n, -0.2);
    }
  
    function randomMixture(dists, weights) {
      var dist = {}, m = 0, w;
  
      function normalize(x) {
        var w = [], sum = 0, i;
        for (i=0; i<m; ++i) { sum += (w[i] = (x[i]==null ? 1 : +x[i])); }
        for (i=0; i<m; ++i) { w[i] /= sum; }
        return w;
      }
  
      dist.weights = function(_) {
        if (arguments.length) {
          w = normalize(weights = (_ || []));
          return dist;
        }
        return weights;
      };
  
      dist.distributions = function(_) {
        if (arguments.length) {
          if (_) {
            m = _.length;
            dists = _;
          } else {
            m = 0;
            dists = [];
          }
          return dist.weights(weights);
        }
        return dists;
      };
  
      dist.sample = function() {
        var r = exports.random(),
            d = dists[m-1],
            v = w[0],
            i = 0;
  
        // first select distribution
        for (; i<m-1; v += w[++i]) {
          if (r < v) { d = dists[i]; break; }
        }
        // then sample from it
        return d.sample();
      };
  
      dist.pdf = function(x) {
        for (var p=0, i=0; i<m; ++i) {
          p += w[i] * dists[i].pdf(x);
        }
        return p;
      };
  
      dist.cdf = function(x) {
        for (var p=0, i=0; i<m; ++i) {
          p += w[i] * dists[i].cdf(x);
        }
        return p;
      };
  
      dist.icdf = function() {
        throw Error('Mixture icdf not supported.');
      };
  
      return dist.distributions(dists).weights(weights);
    }
  
    function randomUniform(min, max) {
      if (max == null) {
        max = (min == null ? 1 : min);
        min = 0;
      }
  
      var dist = {},
          a, b, d;
  
      dist.min = function(_) {
        if (arguments.length) {
          a = _ || 0;
          d = b - a;
          return dist;
        } else {
          return a;
        }
      };
  
      dist.max = function(_) {
        if (arguments.length) {
          b = _ || 0;
          d = b - a;
          return dist;
        } else {
          return b;
        }
      };
  
      dist.sample = function() {
        return a + d * exports.random();
      };
  
      dist.pdf = function(x) {
        return (x >= a && x <= b) ? 1 / d : 0;
      };
  
      dist.cdf = function(x) {
        return x < a ? 0 : x > b ? 1 : (x - a) / d;
      };
  
      dist.icdf = function(p) {
        return (p >= 0 && p <= 1) ? a + p * d : NaN;
      };
  
      return dist.min(min).max(max);
    }
  
    // Ordinary Least Squares
    function ols(uX, uY, uXY, uX2) {
      const delta = uX2 - uX * uX,
            slope = Math.abs(delta) < 1e-24 ? 0 : (uXY - uX * uY) / delta,
            intercept = uY - slope * uX;
  
      return [intercept, slope];
    }
  
    function points(data, x, y, sort) {
      data = data.filter(d => {
        let u = x(d), v = y(d);
        return u != null && (u = +u) >= u && v != null && (v = +v) >= v;
      });
  
      if (sort) {
        data.sort((a, b) => x(a) - x(b));
      }
  
      const X = new Float64Array(data.length),
            Y = new Float64Array(data.length);
  
      let i = 0;
      for (let d of data) {
        X[i] = x(d);
        Y[i] = y(d);
        ++i;
      }
  
      return [X, Y];
    }
  
    function visitPoints(data, x, y, callback) {
      let index = -1, i = -1, u, v;
  
      for (let d of data) {
        u = x(d, ++index, data);
        v = y(d, index, data);
        if (u != null && (u = +u) >= u && v != null && (v = +v) >= v) {
          callback(u, v, ++i);
        }
      }
    }
  
    // Adapted from d3-regression by Harry Stevens
    // License: https://github.com/HarryStevens/d3-regression/blob/master/LICENSE
    function rSquared(data, x, y, uY, predict) {
      let SSE = 0, SST = 0;
  
      visitPoints(data, x, y, (dx, dy) => {
        const sse = dy - predict(dx),
              sst = dy - uY;
  
        SSE += sse * sse;
        SST += sst * sst;
      });
  
      return 1 - SSE / SST;
    }
  
    // Adapted from d3-regression by Harry Stevens
    // License: https://github.com/HarryStevens/d3-regression/blob/master/LICENSE
    function regressionLinear(data, x, y) {
      let X = 0, Y = 0, XY = 0, X2 = 0, n = 0;
  
      visitPoints(data, x, y, (dx, dy) => {
        X += dx;
        Y += dy;
        XY += dx * dy;
        X2 += dx * dx;
        ++n;
      });
  
      const coef = ols(X / n, Y / n, XY / n, X2 / n),
            predict = x => coef[0] + coef[1] * x;
  
      return {
        coef: coef,
        predict: predict,
        rSquared: rSquared(data, x, y, Y / n, predict)
      };
    }
  
    // Adapted from d3-regression by Harry Stevens
    // License: https://github.com/HarryStevens/d3-regression/blob/master/LICENSE
    function regressionLog(data, x, y) {
      let X = 0, Y = 0, XY = 0, X2 = 0, n = 0;
  
      visitPoints(data, x, y, (dx, dy) => {
        dx = Math.log(dx);
        X += dx;
        Y += dy;
        XY += dx * dy;
        X2 += dx * dx;
        ++n;
      });
  
      const coef = ols(X / n, Y / n, XY / n, X2 / n),
            predict = x => coef[0] + coef[1] * Math.log(x);
  
      return {
        coef: coef,
        predict: predict,
        rSquared: rSquared(data, x, y, Y / n, predict)
      };
    }
  
    function regressionExp(data, x, y) {
      let Y = 0, YL = 0, XY = 0, XYL = 0, X2Y = 0, n = 0;
  
      visitPoints(data, x, y, (dx, dy) => {
        const ly = Math.log(dy),
              xy = dx * dy;
        Y += dy;
        XY += xy;
        X2Y += dx * xy;
        YL += dy * ly;
        XYL += xy * ly;
        ++n;
      });
  
      const coef = ols(XY / Y, YL / Y, XYL / Y, X2Y / Y),
            predict = x => coef[0] * Math.exp(coef[1] * x);
  
      coef[0] = Math.exp(coef[0]);
  
      return {
        coef: coef,
        predict: predict,
        rSquared: rSquared(data, x, y, Y / n, predict)
      };
    }
  
    // Adapted from d3-regression by Harry Stevens
    // License: https://github.com/HarryStevens/d3-regression/blob/master/LICENSE
    function regressionPow(data, x, y) {
      let X = 0, Y = 0, XY = 0, X2 = 0, YS = 0, n = 0;
  
      visitPoints(data, x, y, (dx, dy) => {
        const lx = Math.log(dx),
              ly = Math.log(dy);
        X += lx;
        Y += ly;
        XY += lx * ly;
        X2 += lx * lx;
        YS += dy;
        ++n;
      });
  
      const coef = ols(X / n, Y / n, XY / n, X2 / n),
            predict = x => coef[0] * Math.pow(x, coef[1]);
  
      coef[0] = Math.exp(coef[0]);
  
      return {
        coef: coef,
        predict: predict,
        rSquared: rSquared(data, x, y, YS / n, predict)
      };
    }
  
    function regressionQuad(data, x, y) {
      let X = 0, Y = 0, X2 = 0, X3 = 0, X4 = 0, XY = 0, X2Y = 0, n = 0;
  
      visitPoints(data, x, y, (dx, dy) => {
        const x2 = dx * dx;
        X += dx;
        Y += dy;
        X2 += x2;
        X3 += x2 * dx;
        X4 += x2 * x2;
        XY += dx * dy;
        X2Y += x2 * dy;
        ++n;
      });
  
      Y = Y / n;
      XY = XY - X * Y;
      X2Y = X2Y - X2 * Y;
  
      const XX = X2 - X * X / n,
            XX2 = X3 - (X2 * X / n),
            X2X2 = X4 - (X2 * X2 / n),
            d = (XX * X2X2 - XX2 * XX2),
            a = (X2Y * XX - XY * XX2) / d,
            b = (XY * X2X2 - X2Y * XX2) / d,
            c = Y - (b * (X / n)) - (a * (X2 / n)),
            predict = x => a * x * x + b * x + c;
  
      return {
        coef: [c, b, a],
        predict: predict,
        rSquared: rSquared(data, x, y, Y, predict)
      };
    }
  
    // Adapted from d3-regression by Harry Stevens
    // License: https://github.com/HarryStevens/d3-regression/blob/master/LICENSE
    // ... which was adapted from regression-js by Tom Alexander
    // Source: https://github.com/Tom-Alexander/regression-js/blob/master/src/regression.js#L246
    // License: https://github.com/Tom-Alexander/regression-js/blob/master/LICENSE
    function regressionPoly(data, x, y, order) {
      // use more efficient methods for lower orders
      if (order === 1) return regressionLinear(data, x, y);
      if (order === 2) return regressionQuad(data, x, y);
  
      const [xv, yv] = points(data, x, y),
            n = xv.length,
            lhs = [],
            rhs = [],
            k = order + 1;
  
      let Y = 0, i, j, l, v, c;
  
      for (i = 0; i < n; ++i) {
        Y += yv[i];
      }
  
      for (i = 0; i < k; ++i) {
        for (l = 0, v = 0; l < n; ++l) {
          v += Math.pow(xv[l], i) * yv[l];
        }
        lhs.push(v);
  
        c = new Float64Array(k);
        for (j = 0; j < k; ++j) {
          for (l = 0, v = 0; l < n; ++l) {
            v += Math.pow(xv[l], i + j);
          }
          c[j] = v;
        }
        rhs.push(c);
      }
      rhs.push(lhs);
  
      const coef = gaussianElimination(rhs),
            predict = x => {
              let y = 0, i = 0, n = coef.length;
              for (; i < n; ++i) y += coef[i] * Math.pow(x, i);
              return y;
            };
  
      return {
        coef: coef,
        predict: predict,
        rSquared: rSquared(data, x, y, Y / n, predict)
      };
    }
  
    // Given an array for a two-dimensional matrix and the polynomial order,
    // solve A * x = b using Gaussian elimination.
    function gaussianElimination(matrix) {
      const n = matrix.length - 1,
            coef = [];
  
      let i, j, k, r, t;
  
      for (i = 0; i < n; ++i) {
        r = i; // max row
        for (j = i + 1; j < n; ++j) {
          if (Math.abs(matrix[i][j]) > Math.abs(matrix[i][r])) {
            r = j;
          }
        }
  
        for (k = i; k < n + 1; ++k) {
          t = matrix[k][i];
          matrix[k][i] = matrix[k][r];
          matrix[k][r] = t;
        }
  
        for (j = i + 1; j < n; ++j) {
          for (k = n; k >= i; k--) {
            matrix[k][j] -= (matrix[k][i] * matrix[i][j]) / matrix[i][i];
          }
        }
      }
  
      for (j = n - 1; j >= 0; --j) {
        t = 0;
        for (k = j + 1; k < n; ++k) {
          t += matrix[k][j] * coef[k];
        }
        coef[j] = (matrix[n][j] - t) / matrix[j][j];
      }
  
      return coef;
    }
  
    const maxiters = 2,
          epsilon = 1e-12;
  
    // Adapted from science.js by Jason Davies
    // Source: https://github.com/jasondavies/science.js/blob/master/src/stats/loess.js
    // License: https://github.com/jasondavies/science.js/blob/master/LICENSE
    function regressionLoess(data, x, y, bandwidth) {
      const [xv, yv] = points(data, x, y, true),
            n = xv.length,
            bw = Math.max(2, ~~(bandwidth * n)), // # nearest neighbors
            yhat = new Float64Array(n),
            residuals = new Float64Array(n),
            robustWeights = new Float64Array(n).fill(1);
  
      for (let iter = -1; ++iter <= maxiters; ) {
        const interval = [0, bw - 1];
  
        for (let i = 0; i < n; ++i) {
          const dx = xv[i],
                i0 = interval[0],
                i1 = interval[1],
                edge = (dx - xv[i0]) > (xv[i1] - dx) ? i0 : i1;
  
          let W = 0, X = 0, Y = 0, XY = 0, X2 = 0,
              denom = 1 / Math.abs(xv[edge] - dx || 1); // avoid singularity!
  
          for (let k = i0; k <= i1; ++k) {
            const xk = xv[k],
                  yk = yv[k],
                  w = tricube(Math.abs(dx - xk) * denom) * robustWeights[k],
                  xkw = xk * w;
  
            W += w;
            X += xkw;
            Y += yk * w;
            XY += yk * xkw;
            X2 += xk * xkw;
          }
  
          // linear regression fit
          const [a, b] = ols(X / W, Y / W, XY / W, X2 / W);
          yhat[i] = a + b * dx;
          residuals[i] = Math.abs(yv[i] - yhat[i]);
  
          updateInterval(xv, i + 1, interval);
        }
  
        if (iter === maxiters) {
          break;
        }
  
        const medianResidual = d3Array.median(residuals);
        if (Math.abs(medianResidual) < epsilon) break;
  
        for (let i = 0, arg, w; i < n; ++i){
          arg = residuals[i] / (6 * medianResidual);
          // default to epsilon (rather than zero) for large deviations
          // keeping weights tiny but non-zero prevents singularites
          robustWeights[i] = (arg >= 1) ? epsilon : ((w = 1 - arg * arg) * w);
        }
      }
  
      return output(xv, yhat);
    }
  
    // weighting kernel for local regression
    function tricube(x) {
      return (x = 1 - x * x * x) * x * x;
    }
  
    // advance sliding window interval of nearest neighbors
    function updateInterval(xv, i, interval) {
      let val = xv[i],
          left = interval[0],
          right = interval[1] + 1;
  
      if (right >= xv.length) return;
  
      // step right if distance to new right edge is <= distance to old left edge
      // step when distance is equal to ensure movement over duplicate x values
      while (i > left && (xv[right] - val) <= (val - xv[left])) {
        interval[0] = ++left;
        interval[1] = right;
        ++right;
      }
    }
  
    // generate smoothed output points
    // average points with repeated x values
    function output(xv, yhat) {
      const n = xv.length,
            out = [];
  
      for (let i=0, cnt=0, prev=[], v; i<n; ++i) {
        v = xv[i];
        if (prev[0] === v) {
          // average output values via online update
          prev[1] += (yhat[i] - prev[1]) / (++cnt);
        } else {
          // add new output point
          cnt = 0;
          prev = [v, yhat[i]];
          out.push(prev);
        }
      }
      return out;
    }
  
    // subdivide up to accuracy of 0.1 degrees
    const MIN_RADIANS = 0.1 * Math.PI / 180;
  
    // Adaptively sample an interpolated function over a domain extent
    function sampleCurve(f, extent, minSteps, maxSteps) {
      minSteps = minSteps || 25;
      maxSteps = Math.max(minSteps, maxSteps || 200);
  
      const point = x => [x, f(x)],
            minX = extent[0],
            maxX = extent[1],
            span = maxX - minX,
            stop = span / maxSteps,
            prev = [point(minX)],
            next = [];
  
      if (minSteps === maxSteps) {
        // no adaptation, sample uniform grid directly and return
        for (let i = 1; i < maxSteps; ++i) {
          prev.push(point(minX + (i / minSteps) * span));
        }
        prev.push(point(maxX));
        return prev;
      } else {
        // sample minimum points on uniform grid
        // then move on to perform adaptive refinement
        next.push(point(maxX));
        for (let i = minSteps; --i > 0;) {
          next.push(point(minX + (i / minSteps) * span));
        }
      }
  
      let p0 = prev[0],
          p1 = next[next.length - 1];
  
      while (p1) {
        // midpoint for potential curve subdivision
        const pm = point((p0[0] + p1[0]) / 2);
  
        if (pm[0] - p0[0] >= stop && angleDelta(p0, pm, p1) > MIN_RADIANS) {
          // maximum resolution has not yet been met, and
          // subdivision midpoint sufficiently different from endpoint
          // save subdivision, push midpoint onto the visitation stack
          next.push(pm);
        } else {
          // subdivision midpoint sufficiently similar to endpoint
          // skip subdivision, store endpoint, move to next point on the stack
          p0 = p1;
          prev.push(p1);
          next.pop();
        }
        p1 = next[next.length - 1];
      }
  
      return prev;
    }
  
    function angleDelta(p, q, r) {
      const a0 = Math.atan2(r[1] - p[1], r[0] - p[0]),
            a1 = Math.atan2(q[1] - p[1], q[0] - p[0]);
      return Math.abs(a0 - a1);
    }
  
    function TupleStore(key) {
      this._key = key ? field(key) : tupleid;
      this.reset();
    }
  
    var prototype$7 = TupleStore.prototype;
  
    prototype$7.reset = function() {
      this._add = [];
      this._rem = [];
      this._ext = null;
      this._get = null;
      this._q = null;
    };
  
    prototype$7.add = function(v) {
      this._add.push(v);
    };
  
    prototype$7.rem = function(v) {
      this._rem.push(v);
    };
  
    prototype$7.values = function() {
      this._get = null;
      if (this._rem.length === 0) return this._add;
  
      var a = this._add,
          r = this._rem,
          k = this._key,
          n = a.length,
          m = r.length,
          x = Array(n - m),
          map = {}, i, j, v;
  
      // use unique key field to clear removed values
      for (i=0; i<m; ++i) {
        map[k(r[i])] = 1;
      }
      for (i=0, j=0; i<n; ++i) {
        if (map[k(v = a[i])]) {
          map[k(v)] = 0;
        } else {
          x[j++] = v;
        }
      }
  
      this._rem = [];
      return (this._add = x);
    };
  
    // memoizing statistics methods
  
    prototype$7.distinct = function(get) {
      var v = this.values(),
          n = v.length,
          map = {},
          count = 0, s;
  
      while (--n >= 0) {
        s = get(v[n]) + '';
        if (!map.hasOwnProperty(s)) {
          map[s] = 1;
          ++count;
        }
      }
  
      return count;
    };
  
    prototype$7.extent = function(get) {
      if (this._get !== get || !this._ext) {
        var v = this.values(),
            i = extentIndex(v, get);
        this._ext = [v[i[0]], v[i[1]]];
        this._get = get;
      }
      return this._ext;
    };
  
    prototype$7.argmin = function(get) {
      return this.extent(get)[0] || {};
    };
  
    prototype$7.argmax = function(get) {
      return this.extent(get)[1] || {};
    };
  
    prototype$7.min = function(get) {
      var m = this.extent(get)[0];
      return m != null ? get(m) : undefined;
    };
  
    prototype$7.max = function(get) {
      var m = this.extent(get)[1];
      return m != null ? get(m) : undefined;
    };
  
    prototype$7.quartile = function(get) {
      if (this._get !== get || !this._q) {
        this._q = quartiles(this.values(), get);
        this._get = get;
      }
      return this._q;
    };
  
    prototype$7.q1 = function(get) {
      return this.quartile(get)[0];
    };
  
    prototype$7.q2 = function(get) {
      return this.quartile(get)[1];
    };
  
    prototype$7.q3 = function(get) {
      return this.quartile(get)[2];
    };
  
    prototype$7.ci = function(get) {
      if (this._get !== get || !this._ci) {
        this._ci = bootstrapCI(this.values(), 1000, 0.05, get);
        this._get = get;
      }
      return this._ci;
    };
  
    prototype$7.ci0 = function(get) {
      return this.ci(get)[0];
    };
  
    prototype$7.ci1 = function(get) {
      return this.ci(get)[1];
    };
  
    /**
     * Group-by aggregation operator.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors to groupby.
     * @param {Array<function(object): *>} [params.fields] - An array of accessors to aggregate.
     * @param {Array<string>} [params.ops] - An array of strings indicating aggregation operations.
     * @param {Array<string>} [params.as] - An array of output field names for aggregated values.
     * @param {boolean} [params.cross=false] - A flag indicating that the full
     *   cross-product of groupby values should be generated, including empty cells.
     *   If true, the drop parameter is ignored and empty cells are retained.
     * @param {boolean} [params.drop=true] - A flag indicating if empty cells should be removed.
     */
    function Aggregate(params) {
      Transform.call(this, null, params);
  
      this._adds = []; // array of added output tuples
      this._mods = []; // array of modified output tuples
      this._alen = 0;  // number of active added tuples
      this._mlen = 0;  // number of active modified tuples
      this._drop = true;   // should empty aggregation cells be removed
      this._cross = false; // produce full cross-product of group-by values
  
      this._dims = [];   // group-by dimension accessors
      this._dnames = []; // group-by dimension names
  
      this._measures = []; // collection of aggregation monoids
      this._countOnly = false; // flag indicating only count aggregation
      this._counts = null; // collection of count fields
      this._prev = null;   // previous aggregation cells
  
      this._inputs = null;  // array of dependent input tuple field names
      this._outputs = null; // array of output tuple field names
    }
  
    Aggregate.Definition = {
      "type": "Aggregate",
      "metadata": {"generates": true, "changes": true},
      "params": [
        { "name": "groupby", "type": "field", "array": true },
        { "name": "ops", "type": "enum", "array": true, "values": ValidAggregateOps },
        { "name": "fields", "type": "field", "null": true, "array": true },
        { "name": "as", "type": "string", "null": true, "array": true },
        { "name": "drop", "type": "boolean", "default": true },
        { "name": "cross", "type": "boolean", "default": false },
        { "name": "key", "type": "field" }
      ]
    };
  
    var prototype$8 = inherits(Aggregate, Transform);
  
    prototype$8.transform = function(_, pulse) {
      var aggr = this,
          out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS),
          mod;
  
      this.stamp = out.stamp;
  
      if (this.value && ((mod = _.modified()) || pulse.modified(this._inputs))) {
        this._prev = this.value;
        this.value = mod ? this.init(_) : {};
        pulse.visit(pulse.SOURCE, function(t) { aggr.add(t); });
      } else {
        this.value = this.value || this.init(_);
        pulse.visit(pulse.REM, function(t) { aggr.rem(t); });
        pulse.visit(pulse.ADD, function(t) { aggr.add(t); });
      }
  
      // Indicate output fields and return aggregate tuples.
      out.modifies(this._outputs);
  
      // Should empty cells be dropped?
      aggr._drop = _.drop !== false;
  
      // If domain cross-product requested, generate empty cells as needed
      // and ensure that empty cells are not dropped
      if (_.cross && aggr._dims.length > 1) {
        aggr._drop = false;
        this.cross();
      }
  
      return aggr.changes(out);
    };
  
    prototype$8.cross = function() {
      var aggr = this,
          curr = aggr.value,
          dims = aggr._dnames,
          vals = dims.map(function() { return {}; }),
          n = dims.length;
  
      // collect all group-by domain values
      function collect(cells) {
        var key, i, t, v;
        for (key in cells) {
          t = cells[key].tuple;
          for (i=0; i<n; ++i) {
            vals[i][(v = t[dims[i]])] = v;
          }
        }
      }
      collect(aggr._prev);
      collect(curr);
  
      // iterate over key cross-product, create cells as needed
      function generate(base, tuple, index) {
        var name = dims[index],
            v = vals[index++],
            k, key;
  
        for (k in v) {
          tuple[name] = v[k];
          key = base ? base + '|' + k : k;
          if (index < n) generate(key, tuple, index);
          else if (!curr[key]) aggr.cell(key, tuple);
        }
      }
      generate('', {}, 0);
    };
  
    prototype$8.init = function(_) {
      // initialize input and output fields
      var inputs = (this._inputs = []),
          outputs = (this._outputs = []),
          inputMap = {};
  
      function inputVisit(get) {
        var fields = array(accessorFields(get)),
            i = 0, n = fields.length, f;
        for (; i<n; ++i) {
          if (!inputMap[f=fields[i]]) {
            inputMap[f] = 1;
            inputs.push(f);
          }
        }
      }
  
      // initialize group-by dimensions
      this._dims = array(_.groupby);
      this._dnames = this._dims.map(function(d) {
        var dname = accessorName(d);
        inputVisit(d);
        outputs.push(dname);
        return dname;
      });
      this.cellkey = _.key ? _.key : groupkey(this._dims);
  
      // initialize aggregate measures
      this._countOnly = true;
      this._counts = [];
      this._measures = [];
  
      var fields = _.fields || [null],
          ops = _.ops || ['count'],
          as = _.as || [],
          n = fields.length,
          map = {},
          field, op, m, mname, outname, i;
  
      if (n !== ops.length) {
        error('Unmatched number of fields and aggregate ops.');
      }
  
      for (i=0; i<n; ++i) {
        field = fields[i];
        op = ops[i];
  
        if (field == null && op !== 'count') {
          error('Null aggregate field specified.');
        }
        mname = accessorName(field);
        outname = measureName(op, mname, as[i]);
        outputs.push(outname);
  
        if (op === 'count') {
          this._counts.push(outname);
          continue;
        }
  
        m = map[mname];
        if (!m) {
          inputVisit(field);
          m = (map[mname] = []);
          m.field = field;
          this._measures.push(m);
        }
  
        if (op !== 'count') this._countOnly = false;
        m.push(createMeasure(op, outname));
      }
  
      this._measures = this._measures.map(function(m) {
        return compileMeasures(m, m.field);
      });
  
      return {}; // aggregation cells (this.value)
    };
  
    // -- Cell Management -----
  
    prototype$8.cellkey = groupkey();
  
    prototype$8.cell = function(key, t) {
      var cell = this.value[key];
      if (!cell) {
        cell = this.value[key] = this.newcell(key, t);
        this._adds[this._alen++] = cell;
      } else if (cell.num === 0 && this._drop && cell.stamp < this.stamp) {
        cell.stamp = this.stamp;
        this._adds[this._alen++] = cell;
      } else if (cell.stamp < this.stamp) {
        cell.stamp = this.stamp;
        this._mods[this._mlen++] = cell;
      }
      return cell;
    };
  
    prototype$8.newcell = function(key, t) {
      var cell = {
        key:   key,
        num:   0,
        agg:   null,
        tuple: this.newtuple(t, this._prev && this._prev[key]),
        stamp: this.stamp,
        store: false
      };
  
      if (!this._countOnly) {
        var measures = this._measures,
            n = measures.length, i;
  
        cell.agg = Array(n);
        for (i=0; i<n; ++i) {
          cell.agg[i] = new measures[i](cell);
        }
      }
  
      if (cell.store) {
        cell.data = new TupleStore();
      }
  
      return cell;
    };
  
    prototype$8.newtuple = function(t, p) {
      var names = this._dnames,
          dims = this._dims,
          x = {}, i, n;
  
      for (i=0, n=dims.length; i<n; ++i) {
        x[names[i]] = dims[i](t);
      }
  
      return p ? replace(p.tuple, x) : ingest(x);
    };
  
    // -- Process Tuples -----
  
    prototype$8.add = function(t) {
      var key = this.cellkey(t),
          cell = this.cell(key, t),
          agg, i, n;
  
      cell.num += 1;
      if (this._countOnly) return;
  
      if (cell.store) cell.data.add(t);
  
      agg = cell.agg;
      for (i=0, n=agg.length; i<n; ++i) {
        agg[i].add(agg[i].get(t), t);
      }
    };
  
    prototype$8.rem = function(t) {
      var key = this.cellkey(t),
          cell = this.cell(key, t),
          agg, i, n;
  
      cell.num -= 1;
      if (this._countOnly) return;
  
      if (cell.store) cell.data.rem(t);
  
      agg = cell.agg;
      for (i=0, n=agg.length; i<n; ++i) {
        agg[i].rem(agg[i].get(t), t);
      }
    };
  
    prototype$8.celltuple = function(cell) {
      var tuple = cell.tuple,
          counts = this._counts,
          agg, i, n;
  
      // consolidate stored values
      if (cell.store) {
        cell.data.values();
      }
  
      // update tuple properties
      for (i=0, n=counts.length; i<n; ++i) {
        tuple[counts[i]] = cell.num;
      }
      if (!this._countOnly) {
        agg = cell.agg;
        for (i=0, n=agg.length; i<n; ++i) {
          agg[i].set(tuple);
        }
      }
  
      return tuple;
    };
  
    prototype$8.changes = function(out) {
      var adds = this._adds,
          mods = this._mods,
          prev = this._prev,
          drop = this._drop,
          add = out.add,
          rem = out.rem,
          mod = out.mod,
          cell, key, i, n;
  
      if (prev) for (key in prev) {
        cell = prev[key];
        if (!drop || cell.num) rem.push(cell.tuple);
      }
  
      for (i=0, n=this._alen; i<n; ++i) {
        add.push(this.celltuple(adds[i]));
        adds[i] = null; // for garbage collection
      }
  
      for (i=0, n=this._mlen; i<n; ++i) {
        cell = mods[i];
        (cell.num === 0 && drop ? rem : mod).push(this.celltuple(cell));
        mods[i] = null; // for garbage collection
      }
  
      this._alen = this._mlen = 0; // reset list of active cells
      this._prev = null;
      return out;
    };
  
    // epsilon bias to offset floating point error (#1737)
    const EPSILON = 1e-14;
  
    /**
     * Generates a binning function for discretizing data.
     * @constructor
     * @param {object} params - The parameters for this operator. The
     *   provided values should be valid options for the {@link bin} function.
     * @param {function(object): *} params.field - The data field to bin.
     */
    function Bin(params) {
      Transform.call(this, null, params);
    }
  
    Bin.Definition = {
      "type": "Bin",
      "metadata": {"modifies": true},
      "params": [
        { "name": "field", "type": "field", "required": true },
        { "name": "anchor", "type": "number" },
        { "name": "maxbins", "type": "number", "default": 20 },
        { "name": "base", "type": "number", "default": 10 },
        { "name": "divide", "type": "number", "array": true, "default": [5, 2] },
        { "name": "extent", "type": "number", "array": true, "length": 2, "required": true },
        { "name": "step", "type": "number" },
        { "name": "steps", "type": "number", "array": true },
        { "name": "minstep", "type": "number", "default": 0 },
        { "name": "nice", "type": "boolean", "default": true },
        { "name": "name", "type": "string" },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": ["bin0", "bin1"] }
      ]
    };
  
    var prototype$9 = inherits(Bin, Transform);
  
    prototype$9.transform = function(_, pulse) {
      var bins = this._bins(_),
          start = bins.start,
          step = bins.step,
          as = _.as || ['bin0', 'bin1'],
          b0 = as[0],
          b1 = as[1],
          flag;
  
      if (_.modified()) {
        pulse = pulse.reflow(true);
        flag = pulse.SOURCE;
      } else {
        flag = pulse.modified(accessorFields(_.field)) ? pulse.ADD_MOD : pulse.ADD;
      }
  
      pulse.visit(flag, function(t) {
        var v = bins(t);
        // minimum bin value (inclusive)
        t[b0] = v;
        // maximum bin value (exclusive)
        // use convoluted math for better floating point agreement
        // see https://github.com/vega/vega/issues/830
        t[b1] = v == null ? null : start + step * (1 + (v - start) / step);
      });
  
      return pulse.modifies(as);
    };
  
    prototype$9._bins = function(_) {
      if (this.value && !_.modified()) {
        return this.value;
      }
  
      var field = _.field,
          bins  = bin(_),
          start = bins.start,
          stop  = bins.stop,
          step  = bins.step,
          a, d;
  
      if ((a = _.anchor) != null) {
        d = a - (start + step * Math.floor((a - start) / step));
        start += d;
        stop += d;
      }
  
      var f = function(t) {
        var v = field(t);
        if (v == null) {
          return null;
        } else {
          v = Math.max(start, Math.min(+v, stop - step));
          return start + step * Math.floor(EPSILON + (v - start) / step);
        }
      };
  
      f.start = start;
      f.stop = stop;
      f.step = step;
  
      return this.value = accessor(
        f,
        accessorFields(field),
        _.name || 'bin_' + accessorName(field)
      );
    };
  
    function SortedList(idFunc, source, input) {
      var $ = idFunc,
          data = source || [],
          add = input || [],
          rem = {},
          cnt = 0;
  
      return {
        add: function(t) { add.push(t); },
        remove: function(t) { rem[$(t)] = ++cnt; },
        size: function() { return data.length; },
        data: function(compare, resort) {
          if (cnt) {
            data = data.filter(function(t) { return !rem[$(t)]; });
            rem = {};
            cnt = 0;
          }
          if (resort && compare) {
            data.sort(compare);
          }
          if (add.length) {
            data = compare
              ? merge(compare, data, add.sort(compare))
              : data.concat(add);
            add = [];
          }
          return data;
        }
      }
    }
  
    /**
     * Collects all data tuples that pass through this operator.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(*,*): number} [params.sort] - An optional
     *   comparator function for additionally sorting the collected tuples.
     */
    function Collect(params) {
      Transform.call(this, [], params);
    }
  
    Collect.Definition = {
      "type": "Collect",
      "metadata": {"source": true},
      "params": [
        { "name": "sort", "type": "compare" }
      ]
    };
  
    var prototype$a = inherits(Collect, Transform);
  
    prototype$a.transform = function(_, pulse) {
      var out = pulse.fork(pulse.ALL),
          list = SortedList(tupleid, this.value, out.materialize(out.ADD).add),
          sort = _.sort,
          mod = pulse.changed() || (sort &&
                (_.modified('sort') || pulse.modified(sort.fields)));
  
      out.visit(out.REM, list.remove);
  
      this.modified(mod);
      this.value = out.source = list.data(sort, mod);
  
      // propagate tree root if defined
      if (pulse.source && pulse.source.root) {
        this.value.root = pulse.source.root;
      }
  
      return out;
    };
  
    /**
     * Generates a comparator function.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<string|function>} params.fields - The fields to compare.
     * @param {Array<string>} [params.orders] - The sort orders.
     *   Each entry should be one of "ascending" (default) or "descending".
     */
    function Compare(params) {
      Operator.call(this, null, update$1, params);
    }
  
    inherits(Compare, Operator);
  
    function update$1(_) {
      return (this.value && !_.modified())
        ? this.value
        : compare(_.fields, _.orders);
    }
  
    /**
     * Count regexp-defined pattern occurrences in a text field.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - An accessor for the text field.
     * @param {string} [params.pattern] - RegExp string defining the text pattern.
     * @param {string} [params.case] - One of 'lower', 'upper' or null (mixed) case.
     * @param {string} [params.stopwords] - RegExp string of words to ignore.
     */
    function CountPattern(params) {
      Transform.call(this, null, params);
    }
  
    CountPattern.Definition = {
      "type": "CountPattern",
      "metadata": {"generates": true, "changes": true},
      "params": [
        { "name": "field", "type": "field", "required": true },
        { "name": "case", "type": "enum", "values": ["upper", "lower", "mixed"], "default": "mixed" },
        { "name": "pattern", "type": "string", "default": "[\\w\"]+" },
        { "name": "stopwords", "type": "string", "default": "" },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": ["text", "count"] }
      ]
    };
  
    function tokenize(text, tcase, match) {
      switch (tcase) {
        case 'upper': text = text.toUpperCase(); break;
        case 'lower': text = text.toLowerCase(); break;
      }
      return text.match(match);
    }
  
    var prototype$b = inherits(CountPattern, Transform);
  
    prototype$b.transform = function(_, pulse) {
      function process(update) {
        return function(tuple) {
          var tokens = tokenize(get(tuple), _.case, match) || [], t;
          for (var i=0, n=tokens.length; i<n; ++i) {
            if (!stop.test(t = tokens[i])) update(t);
          }
        };
      }
  
      var init = this._parameterCheck(_, pulse),
          counts = this._counts,
          match = this._match,
          stop = this._stop,
          get = _.field,
          as = _.as || ['text', 'count'],
          add = process(function(t) { counts[t] = 1 + (counts[t] || 0); }),
          rem = process(function(t) { counts[t] -= 1; });
  
      if (init) {
        pulse.visit(pulse.SOURCE, add);
      } else {
        pulse.visit(pulse.ADD, add);
        pulse.visit(pulse.REM, rem);
      }
  
      return this._finish(pulse, as); // generate output tuples
    };
  
    prototype$b._parameterCheck = function(_, pulse) {
      var init = false;
  
      if (_.modified('stopwords') || !this._stop) {
        this._stop = new RegExp('^' + (_.stopwords || '') + '$', 'i');
        init = true;
      }
  
      if (_.modified('pattern') || !this._match) {
        this._match = new RegExp((_.pattern || '[\\w\']+'), 'g');
        init = true;
      }
  
      if (_.modified('field') || pulse.modified(_.field.fields)) {
        init = true;
      }
  
      if (init) this._counts = {};
      return init;
    };
  
    prototype$b._finish = function(pulse, as) {
      var counts = this._counts,
          tuples = this._tuples || (this._tuples = {}),
          text = as[0],
          count = as[1],
          out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS),
          w, t, c;
  
      for (w in counts) {
        t = tuples[w];
        c = counts[w] || 0;
        if (!t && c) {
          tuples[w] = (t = ingest({}));
          t[text] = w;
          t[count] = c;
          out.add.push(t);
        } else if (c === 0) {
          if (t) out.rem.push(t);
          counts[w] = null;
          tuples[w] = null;
        } else if (t[count] !== c) {
          t[count] = c;
          out.mod.push(t);
        }
      }
  
      return out.modifies(as);
    };
  
    /**
     * Perform a cross-product of a tuple stream with itself.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object):boolean} [params.filter] - An optional filter
     *   function for selectively including tuples in the cross product.
     * @param {Array<string>} [params.as] - The names of the output fields.
     */
    function Cross(params) {
      Transform.call(this, null, params);
    }
  
    Cross.Definition = {
      "type": "Cross",
      "metadata": {"generates": true},
      "params": [
        { "name": "filter", "type": "expr" },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": ["a", "b"] }
      ]
    };
  
    var prototype$c = inherits(Cross, Transform);
  
    prototype$c.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE),
          data = this.value,
          as = _.as || ['a', 'b'],
          a = as[0], b = as[1],
          reset = !data
              || pulse.changed(pulse.ADD_REM)
              || _.modified('as')
              || _.modified('filter');
  
      if (reset) {
        if (data) out.rem = data;
        data = pulse.materialize(pulse.SOURCE).source;
        out.add = this.value = cross(data, a, b, _.filter || truthy);
      } else {
        out.mod = data;
      }
  
      out.source = this.value;
      return out.modifies(as);
    };
  
    function cross(input, a, b, filter) {
      var data = [],
          t = {},
          n = input.length,
          i = 0,
          j, left;
  
      for (; i<n; ++i) {
        t[a] = left = input[i];
        for (j=0; j<n; ++j) {
          t[b] = input[j];
          if (filter(t)) {
            data.push(ingest(t));
            t = {};
            t[a] = left;
          }
        }
      }
  
      return data;
    }
  
    var Distributions = {
      kde:     randomKDE,
      mixture: randomMixture,
      normal:  randomNormal,
      uniform: randomUniform
    };
  
    var DISTRIBUTIONS = 'distributions',
        FUNCTION = 'function',
        FIELD = 'field';
  
    /**
     * Parse a parameter object for a probability distribution.
     * @param {object} def - The distribution parameter object.
     * @param {function():Array<object>} - A method for requesting
     *   source data. Used for distributions (such as KDE) that
     *   require sample data points. This method will only be
     *   invoked if the 'from' parameter for a target data source
     *   is not provided. Typically this method returns backing
     *   source data for a Pulse object.
     * @return {object} - The output distribution object.
     */
    function parse$2(def, data) {
      var func = def[FUNCTION];
      if (!Distributions.hasOwnProperty(func)) {
        error('Unknown distribution function: ' + func);
      }
  
      var d = Distributions[func]();
  
      for (var name in def) {
        // if data field, extract values
        if (name === FIELD) {
          d.data((def.from || data()).map(def[name]));
        }
  
        // if distribution mixture, recurse to parse each definition
        else if (name === DISTRIBUTIONS) {
          d[name](def[name].map(function(_) { return parse$2(_, data); }));
        }
  
        // otherwise, simply set the parameter
        else if (typeof d[name] === FUNCTION) {
          d[name](def[name]);
        }
      }
  
      return d;
    }
  
    /**
     * Grid sample points for a probability density. Given a distribution and
     * a sampling extent, will generate points suitable for plotting either
     * PDF (probability density function) or CDF (cumulative distribution
     * function) curves.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {object} params.distribution - The probability distribution. This
     *   is an object parameter dependent on the distribution type.
     * @param {string} [params.method='pdf'] - The distribution method to sample.
     *   One of 'pdf' or 'cdf'.
     * @param {Array<number>} [params.extent] - The [min, max] extent over which
     *   to sample the distribution. This argument is required in most cases, but
     *   can be omitted if the distribution (e.g., 'kde') supports a 'data' method
     *   that returns numerical sample points from which the extent can be deduced.
     * @param {number} [params.minsteps=25] - The minimum number of curve samples
     *   for plotting the density.
     * @param {number} [params.maxsteps=200] - The maximum number of curve samples
     *   for plotting the density.
     * @param {number} [params.steps] - The exact number of curve samples for
     *   plotting the density. If specified, overrides both minsteps and maxsteps
     *   to set an exact number of uniform samples. Useful in conjunction with
     *   a fixed extent to ensure consistent sample points for stacked densities.
     */
    function Density(params) {
      Transform.call(this, null, params);
    }
  
    var distributions = [
      {
        "key": {"function": "normal"},
        "params": [
          { "name": "mean", "type": "number", "default": 0 },
          { "name": "stdev", "type": "number", "default": 1 }
        ]
      },
      {
        "key": {"function": "uniform"},
        "params": [
          { "name": "min", "type": "number", "default": 0 },
          { "name": "max", "type": "number", "default": 1 }
        ]
      },
      {
        "key": {"function": "kde"},
        "params": [
          { "name": "field", "type": "field", "required": true },
          { "name": "from", "type": "data" },
          { "name": "bandwidth", "type": "number", "default": 0 }
        ]
      }
    ];
  
    var mixture = {
      "key": {"function": "mixture"},
      "params": [
        { "name": "distributions", "type": "param", "array": true,
          "params": distributions },
        { "name": "weights", "type": "number", "array": true }
      ]
    };
  
    Density.Definition = {
      "type": "Density",
      "metadata": {"generates": true},
      "params": [
        { "name": "extent", "type": "number", "array": true, "length": 2 },
        { "name": "steps", "type": "number" },
        { "name": "minsteps", "type": "number", "default": 25 },
        { "name": "maxsteps", "type": "number", "default": 200 },
        { "name": "method", "type": "string", "default": "pdf",
          "values": ["pdf", "cdf"] },
        { "name": "distribution", "type": "param",
          "params": distributions.concat(mixture) },
        { "name": "as", "type": "string", "array": true,
          "default": ["value", "density"] }
      ]
    };
  
    var prototype$d = inherits(Density, Transform);
  
    prototype$d.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);
  
      if (!this.value || pulse.changed() || _.modified()) {
        var dist = parse$2(_.distribution, source(pulse)),
            minsteps = _.steps || _.minsteps || 25,
            maxsteps = _.steps || _.maxsteps || 200,
            method = _.method || 'pdf';
  
        if (method !== 'pdf' && method !== 'cdf') {
          error('Invalid density method: ' + method);
        }
        if (!_.extent && !dist.data) {
          error('Missing density extent parameter.');
        }
        method = dist[method];
  
        var as = _.as || ['value', 'density'],
            domain = _.extent || extent(dist.data()),
            values = sampleCurve(method, domain, minsteps, maxsteps).map(v => {
              var tuple = {};
              tuple[as[0]] = v[0];
              tuple[as[1]] = v[1];
              return ingest(tuple);
            });
  
        if (this.value) out.rem = this.value;
        this.value = out.add = out.source = values;
      }
  
      return out;
    };
  
    function source(pulse) {
      return function() { return pulse.materialize(pulse.SOURCE).source; };
    }
  
    /**
     * Wraps an expression function with access to external parameters.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function} params.expr - The expression function. The
     *  function should accept both a datum and a parameter object.
     *  This operator's value will be a new function that wraps the
     *  expression function with access to this operator's parameters.
     */
    function Expression(params) {
      Operator.call(this, null, update$2, params);
      this.modified(true);
    }
  
    inherits(Expression, Operator);
  
    function update$2(_) {
      var expr = _.expr;
      return this.value && !_.modified('expr')
        ? this.value
        : accessor(
            datum => expr(datum, _),
            accessorFields(expr),
            accessorName(expr)
          );
    }
  
    /**
     * Computes extents (min/max) for a data field.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The field over which to compute extends.
     */
    function Extent(params) {
      Transform.call(this, [undefined, undefined], params);
    }
  
    Extent.Definition = {
      "type": "Extent",
      "metadata": {},
      "params": [
        { "name": "field", "type": "field", "required": true }
      ]
    };
  
    var prototype$e = inherits(Extent, Transform);
  
    prototype$e.transform = function(_, pulse) {
      var extent = this.value,
          field = _.field,
          min = extent[0],
          max = extent[1],
          mod;
  
      mod = pulse.changed()
         || pulse.modified(field.fields)
         || _.modified('field');
  
      if (mod || min == null) {
        min = +Infinity;
        max = -Infinity;
      }
  
      pulse.visit(mod ? pulse.SOURCE : pulse.ADD, function(t) {
        var v = field(t);
        if (v != null) {
          // coerce to number
          v = +v;
          // NaNs will fail all comparisons!
          if (v < min) min = v;
          if (v > max) max = v;
        }
      });
  
      if (!isFinite(min) || !isFinite(max)) {
        min = max = undefined;
      }
      this.value = [min, max];
    };
  
    /**
     * Provides a bridge between a parent transform and a target subflow that
     * consumes only a subset of the tuples that pass through the parent.
     * @constructor
     * @param {Pulse} pulse - A pulse to use as the value of this operator.
     * @param {Transform} parent - The parent transform (typically a Facet instance).
     * @param {Transform} target - A transform that receives the subflow of tuples.
     */
    function Subflow(pulse, parent) {
      Operator.call(this, pulse);
      this.parent = parent;
    }
  
    var prototype$f = inherits(Subflow, Operator);
  
    prototype$f.connect = function(target) {
      this.targets().add(target);
      return (target.source = this);
    };
  
    /**
     * Add an 'add' tuple to the subflow pulse.
     * @param {Tuple} t - The tuple being added.
     */
    prototype$f.add = function(t) {
      this.value.add.push(t);
    };
  
    /**
     * Add a 'rem' tuple to the subflow pulse.
     * @param {Tuple} t - The tuple being removed.
     */
    prototype$f.rem = function(t) {
      this.value.rem.push(t);
    };
  
    /**
     * Add a 'mod' tuple to the subflow pulse.
     * @param {Tuple} t - The tuple being modified.
     */
    prototype$f.mod = function(t) {
      this.value.mod.push(t);
    };
  
    /**
     * Re-initialize this operator's pulse value.
     * @param {Pulse} pulse - The pulse to copy from.
     * @see Pulse.init
     */
    prototype$f.init = function(pulse) {
      this.value.init(pulse, pulse.NO_SOURCE);
    };
  
    /**
     * Evaluate this operator. This method overrides the
     * default behavior to simply return the contained pulse value.
     * @return {Pulse}
     */
    prototype$f.evaluate = function() {
      // assert: this.value.stamp === pulse.stamp
      return this.value;
    };
  
    /**
     * Facets a dataflow into a set of subflows based on a key.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(Dataflow, string): Operator} params.subflow - A function
     *   that generates a subflow of operators and returns its root operator.
     * @param {function(object): *} params.key - The key field to facet by.
     */
    function Facet(params) {
      Transform.call(this, {}, params);
      this._keys = fastmap(); // cache previously calculated key values
  
      // keep track of active subflows, use as targets array for listeners
      // this allows us to limit propagation to only updated subflows
      var a = this._targets = [];
      a.active = 0;
      a.forEach = function(f) {
        for (var i=0, n=a.active; i<n; ++i) f(a[i], i, a);
      };
    }
  
    var prototype$g = inherits(Facet, Transform);
  
    prototype$g.activate = function(flow) {
      this._targets[this._targets.active++] = flow;
    };
  
    prototype$g.subflow = function(key, flow, pulse, parent) {
      var flows = this.value,
          sf = flows.hasOwnProperty(key) && flows[key],
          df, p;
  
      if (!sf) {
        p = parent || (p = this._group[key]) && p.tuple;
        df = pulse.dataflow;
        sf = df.add(new Subflow(pulse.fork(pulse.NO_SOURCE), this))
          .connect(flow(df, key, p));
        flows[key] = sf;
        this.activate(sf);
      } else if (sf.value.stamp < pulse.stamp) {
        sf.init(pulse);
        this.activate(sf);
      }
  
      return sf;
    };
  
    prototype$g.transform = function(_, pulse) {
      var df = pulse.dataflow,
          self = this,
          key = _.key,
          flow = _.subflow,
          cache = this._keys,
          rekey = _.modified('key');
  
      function subflow(key) {
        return self.subflow(key, flow, pulse);
      }
  
      this._group = _.group || {};
      this._targets.active = 0; // reset list of active subflows
  
      pulse.visit(pulse.REM, function(t) {
        var id = tupleid(t),
            k = cache.get(id);
        if (k !== undefined) {
          cache.delete(id);
          subflow(k).rem(t);
        }
      });
  
      pulse.visit(pulse.ADD, function(t) {
        var k = key(t);
        cache.set(tupleid(t), k);
        subflow(k).add(t);
      });
  
      if (rekey || pulse.modified(key.fields)) {
        pulse.visit(pulse.MOD, function(t) {
          var id = tupleid(t),
              k0 = cache.get(id),
              k1 = key(t);
          if (k0 === k1) {
            subflow(k1).mod(t);
          } else {
            cache.set(id, k1);
            subflow(k0).rem(t);
            subflow(k1).add(t);
          }
        });
      } else if (pulse.changed(pulse.MOD)) {
        pulse.visit(pulse.MOD, function(t) {
          subflow(cache.get(tupleid(t))).mod(t);
        });
      }
  
      if (rekey) {
        pulse.visit(pulse.REFLOW, function(t) {
          var id = tupleid(t),
              k0 = cache.get(id),
              k1 = key(t);
          if (k0 !== k1) {
            cache.set(id, k1);
            subflow(k0).rem(t);
            subflow(k1).add(t);
          }
        });
      }
  
      if (cache.empty > df.cleanThreshold) df.runAfter(cache.clean);
      return pulse;
    };
  
    /**
     * Generates one or more field accessor functions.
     * If the 'name' parameter is an array, an array of field accessors
     * will be created and the 'as' parameter will be ignored.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {string} params.name - The field name(s) to access.
     * @param {string} params.as - The accessor function name.
     */
    function Field(params) {
      Operator.call(this, null, update$3, params);
    }
  
    inherits(Field, Operator);
  
    function update$3(_) {
      return (this.value && !_.modified()) ? this.value
        : isArray(_.name) ? array(_.name).map(function(f) { return field(f); })
        : field(_.name, _.as);
    }
  
    /**
     * Filters data tuples according to a predicate function.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.expr - The predicate expression function
     *   that determines a tuple's filter status. Truthy values pass the filter.
     */
    function Filter(params) {
      Transform.call(this, fastmap(), params);
    }
  
    Filter.Definition = {
      "type": "Filter",
      "metadata": {"changes": true},
      "params": [
        { "name": "expr", "type": "expr", "required": true }
      ]
    };
  
    var prototype$h = inherits(Filter, Transform);
  
    prototype$h.transform = function(_, pulse) {
      var df = pulse.dataflow,
          cache = this.value, // cache ids of filtered tuples
          output = pulse.fork(),
          add = output.add,
          rem = output.rem,
          mod = output.mod,
          test = _.expr,
          isMod = true;
  
      pulse.visit(pulse.REM, function(t) {
        var id = tupleid(t);
        if (!cache.has(id)) rem.push(t);
        else cache.delete(id);
      });
  
      pulse.visit(pulse.ADD, function(t) {
        if (test(t, _)) add.push(t);
        else cache.set(tupleid(t), 1);
      });
  
      function revisit(t) {
        var id = tupleid(t),
            b = test(t, _),
            s = cache.get(id);
        if (b && s) {
          cache.delete(id);
          add.push(t);
        } else if (!b && !s) {
          cache.set(id, 1);
          rem.push(t);
        } else if (isMod && b && !s) {
          mod.push(t);
        }
      }
  
      pulse.visit(pulse.MOD, revisit);
  
      if (_.modified()) {
        isMod = false;
        pulse.visit(pulse.REFLOW, revisit);
      }
  
      if (cache.empty > df.cleanThreshold) df.runAfter(cache.clean);
      return output;
    };
  
    // use either provided alias or accessor field name
    function fieldNames(fields, as) {
      if (!fields) return null;
      return fields.map(function(f, i) {
        return as[i] || accessorName(f);
      });
    }
  
    /**
     * Flattens array-typed field values into new data objects.
     * If multiple fields are specified, they are treated as parallel arrays,
     * with output values included for each matching index (or null if missing).
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<function(object): *>} params.fields - An array of field
     *   accessors for the tuple fields that should be flattened.
     * @param {Array<string>} [params.as] - Output field names for flattened
     *   array fields. Any unspecified fields will use the field name provided
     *   by the fields accessors.
     */
    function Flatten(params) {
      Transform.call(this, [], params);
    }
  
    Flatten.Definition = {
      "type": "Flatten",
      "metadata": {"generates": true},
      "params": [
        { "name": "fields", "type": "field", "array": true, "required": true },
        { "name": "as", "type": "string", "array": true }
      ]
    };
  
    var prototype$i = inherits(Flatten, Transform);
  
    prototype$i.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE),
          fields = _.fields,
          as = fieldNames(fields, _.as || []),
          m = as.length;
  
      // remove any previous results
      out.rem = this.value;
  
      // generate flattened tuples
      pulse.visit(pulse.SOURCE, function(t) {
        var arrays = fields.map(function(f) { return f(t); }),
            maxlen = arrays.reduce(function(l, a) { return Math.max(l, a.length); }, 0),
            i = 0, j, d, v;
  
        for (; i<maxlen; ++i) {
          d = derive(t);
          for (j=0; j<m; ++j) {
            d[as[j]] = (v = arrays[j][i]) == null ? null : v;
          }
          out.add.push(d);
        }
      });
  
      this.value = out.source = out.add;
      return out.modifies(as);
    };
  
    /**
     * Folds one more tuple fields into multiple tuples in which the field
     * name and values are available under new 'key' and 'value' fields.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.fields - An array of field accessors
     *   for the tuple fields that should be folded.
     * @param {Array<string>} [params.as] - Output field names for folded key
     *   and value fields, defaults to ['key', 'value'].
     */
    function Fold(params) {
      Transform.call(this, [], params);
    }
  
    Fold.Definition = {
      "type": "Fold",
      "metadata": {"generates": true},
      "params": [
        { "name": "fields", "type": "field", "array": true, "required": true },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": ["key", "value"] }
      ]
    };
  
    var prototype$j = inherits(Fold, Transform);
  
    prototype$j.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE),
          fields = _.fields,
          fnames = fields.map(accessorName),
          as = _.as || ['key', 'value'],
          k = as[0],
          v = as[1],
          n = fields.length;
  
      out.rem = this.value;
  
      pulse.visit(pulse.SOURCE, function(t) {
        for (var i=0, d; i<n; ++i) {
          d = derive(t);
          d[k] = fnames[i];
          d[v] = fields[i](t);
          out.add.push(d);
        }
      });
  
      this.value = out.source = out.add;
      return out.modifies(as);
    };
  
    /**
     * Invokes a function for each data tuple and saves the results as a new field.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.expr - The formula function to invoke for each tuple.
     * @param {string} params.as - The field name under which to save the result.
     * @param {boolean} [params.initonly=false] - If true, the formula is applied to
     *   added tuples only, and does not update in response to modifications.
     */
    function Formula(params) {
      Transform.call(this, null, params);
    }
  
    Formula.Definition = {
      "type": "Formula",
      "metadata": {"modifies": true},
      "params": [
        { "name": "expr", "type": "expr", "required": true },
        { "name": "as", "type": "string", "required": true },
        { "name": "initonly", "type": "boolean" }
      ]
    };
  
    var prototype$k = inherits(Formula, Transform);
  
    prototype$k.transform = function(_, pulse) {
      var func = _.expr,
          as = _.as,
          mod = _.modified(),
          flag = _.initonly ? pulse.ADD
            : mod ? pulse.SOURCE
            : pulse.modified(func.fields) ? pulse.ADD_MOD
            : pulse.ADD;
  
      function set(t) {
        t[as] = func(t, _);
      }
  
      if (mod) {
        // parameters updated, need to reflow
        pulse = pulse.materialize().reflow(true);
      }
  
      if (!_.initonly) {
        pulse.modifies(as);
      }
  
      return pulse.visit(flag, set);
    };
  
    /**
     * Generates data tuples using a provided generator function.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(Parameters): object} params.generator - A tuple generator
     *   function. This function is given the operator parameters as input.
     *   Changes to any additional parameters will not trigger re-calculation
     *   of previously generated tuples. Only future tuples are affected.
     * @param {number} params.size - The number of tuples to produce.
     */
    function Generate(params) {
      Transform.call(this, [], params);
    }
  
    var prototype$l = inherits(Generate, Transform);
  
    prototype$l.transform = function(_, pulse) {
      var data = this.value,
          out = pulse.fork(pulse.ALL),
          num = _.size - data.length,
          gen = _.generator,
          add, rem, t;
  
      if (num > 0) {
        // need more tuples, generate and add
        for (add=[]; --num >= 0;) {
          add.push(t = ingest(gen(_)));
          data.push(t);
        }
        out.add = out.add.length
          ? out.materialize(out.ADD).add.concat(add)
          : add;
      } else {
        // need fewer tuples, remove
        rem = data.slice(0, -num);
        out.rem = out.rem.length
          ? out.materialize(out.REM).rem.concat(rem)
          : rem;
        data = data.slice(-num);
      }
  
      out.source = this.value = data;
      return out;
    };
  
    var Methods = {
      value: 'value',
      median: d3Array.median,
      mean: d3Array.mean,
      min: d3Array.min,
      max: d3Array.max
    };
  
    var Empty = [];
  
    /**
     * Impute missing values.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The value field to impute.
     * @param {Array<function(object): *>} [params.groupby] - An array of
     *   accessors to determine series within which to perform imputation.
     * @param {function(object): *} params.key - An accessor for a key value.
     *   Each key value should be unique within a group. New tuples will be
     *   imputed for any key values that are not found within a group.
     * @param {Array<*>} [params.keyvals] - Optional array of required key
     *   values. New tuples will be imputed for any key values that are not
     *   found within a group. In addition, these values will be automatically
     *   augmented with the key values observed in the input data.
     * @param {string} [method='value'] - The imputation method to use. One of
     *   'value', 'mean', 'median', 'max', 'min'.
     * @param {*} [value=0] - The constant value to use for imputation
     *   when using method 'value'.
     */
    function Impute(params) {
      Transform.call(this, [], params);
    }
  
    Impute.Definition = {
      "type": "Impute",
      "metadata": {"changes": true},
      "params": [
        { "name": "field", "type": "field", "required": true },
        { "name": "key", "type": "field", "required": true },
        { "name": "keyvals", "array": true },
        { "name": "groupby", "type": "field", "array": true },
        { "name": "method", "type": "enum", "default": "value",
          "values": ["value", "mean", "median", "max", "min"] },
        { "name": "value", "default": 0 }
      ]
    };
  
    var prototype$m = inherits(Impute, Transform);
  
    function getValue(_) {
      var m = _.method || Methods.value, v;
  
      if (Methods[m] == null) {
        error('Unrecognized imputation method: ' + m);
      } else if (m === Methods.value) {
        v = _.value !== undefined ? _.value : 0;
        return function() { return v; };
      } else {
        return Methods[m];
      }
    }
  
    function getField(_) {
      var f = _.field;
      return function(t) { return t ? f(t) : NaN; };
    }
  
    prototype$m.transform = function(_, pulse) {
      var out = pulse.fork(pulse.ALL),
          impute = getValue(_),
          field = getField(_),
          fName = accessorName(_.field),
          kName = accessorName(_.key),
          gNames = (_.groupby || []).map(accessorName),
          groups = partition(pulse.source, _.groupby, _.key, _.keyvals),
          curr = [],
          prev = this.value,
          m = groups.domain.length,
          group, value, gVals, kVal, g, i, j, l, n, t;
  
      for (g=0, l=groups.length; g<l; ++g) {
        group = groups[g];
        gVals = group.values;
        value = NaN;
  
        // add tuples for missing values
        for (j=0; j<m; ++j) {
          if (group[j] != null) continue;
          kVal = groups.domain[j];
  
          t = {_impute: true};
          for (i=0, n=gVals.length; i<n; ++i) t[gNames[i]] = gVals[i];
          t[kName] = kVal;
          t[fName] = isNaN(value) ? (value = impute(group, field)) : value;
  
          curr.push(ingest(t));
        }
      }
  
      // update pulse with imputed tuples
      if (curr.length) out.add = out.materialize(out.ADD).add.concat(curr);
      if (prev.length) out.rem = out.materialize(out.REM).rem.concat(prev);
      this.value = curr;
  
      return out;
    };
  
    function partition(data, groupby, key, keyvals) {
      var get = function(f) { return f(t); },
          groups = [],
          domain = keyvals ? keyvals.slice() : [],
          kMap = {},
          gMap = {}, gVals, gKey,
          group, i, j, k, n, t;
  
      domain.forEach(function(k, i) { kMap[k] = i + 1; });
  
      for (i=0, n=data.length; i<n; ++i) {
        t = data[i];
        k = key(t);
        j = kMap[k] || (kMap[k] = domain.push(k));
  
        gKey = (gVals = groupby ? groupby.map(get) : Empty) + '';
        if (!(group = gMap[gKey])) {
          group = (gMap[gKey] = []);
          groups.push(group);
          group.values = gVals;
        }
        group[j-1] = t;
      }
  
      groups.domain = domain;
      return groups;
    }
  
    /**
     * Extend input tuples with aggregate values.
     * Calcuates aggregate values and joins them with the input stream.
     * @constructor
     */
    function JoinAggregate(params) {
      Aggregate.call(this, params);
    }
  
    JoinAggregate.Definition = {
      "type": "JoinAggregate",
      "metadata": {"modifies": true},
      "params": [
        { "name": "groupby", "type": "field", "array": true },
        { "name": "fields", "type": "field", "null": true, "array": true },
        { "name": "ops", "type": "enum", "array": true, "values": ValidAggregateOps },
        { "name": "as", "type": "string", "null": true, "array": true },
        { "name": "key", "type": "field" }
      ]
    };
  
    var prototype$n = inherits(JoinAggregate, Aggregate);
  
    prototype$n.transform = function(_, pulse) {
      var aggr = this,
          mod = _.modified(),
          cells;
  
      // process all input tuples to calculate aggregates
      if (aggr.value && (mod || pulse.modified(aggr._inputs))) {
        cells = aggr.value = mod ? aggr.init(_) : {};
        pulse.visit(pulse.SOURCE, function(t) { aggr.add(t); });
      } else {
        cells = aggr.value = aggr.value || this.init(_);
        pulse.visit(pulse.REM, function(t) { aggr.rem(t); });
        pulse.visit(pulse.ADD, function(t) { aggr.add(t); });
      }
  
      // update aggregation cells
      aggr.changes();
  
      // write aggregate values to input tuples
      pulse.visit(pulse.SOURCE, function(t) {
        extend(t, cells[aggr.cellkey(t)].tuple);
      });
  
      return pulse.reflow(mod).modifies(this._outputs);
    };
  
    prototype$n.changes = function() {
      var adds = this._adds,
          mods = this._mods,
          i, n;
  
      for (i=0, n=this._alen; i<n; ++i) {
        this.celltuple(adds[i]);
        adds[i] = null; // for garbage collection
      }
  
      for (i=0, n=this._mlen; i<n; ++i) {
        this.celltuple(mods[i]);
        mods[i] = null; // for garbage collection
      }
  
      this._alen = this._mlen = 0; // reset list of active cells
    };
  
    /**
     * Compute kernel density estimates (KDE) for one or more data groups.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors
     *   to groupby.
     * @param {function(object): *} params.field - An accessor for the data field
     *   to estimate.
     * @param {number} [params.bandwidth=0] - The KDE kernal bandwidth.
     *   If zero of unspecified, the bandwidth is automatically determined.
     * @param {string} [params.cumulative=false] - A boolean flag indicating if a
     *   density (false) or cumulative distribution (true) should be generated.
     * @param {Array<number>} [params.extent] - The domain extent over which to
     *   plot the density. If unspecified, the [min, max] data extent is used.
     * @param {number} [params.minsteps=25] - The minimum number of curve samples
     *   for plotting the density.
     * @param {number} [params.maxsteps=200] - The maximum number of curve samples
     *   for plotting the density.
     * @param {number} [params.steps] - The exact number of curve samples for
     *   plotting the density. If specified, overrides both minsteps and maxsteps
     *   to set an exact number of uniform samples. Useful in conjunction with
     *   a fixed extent to ensure consistent sample points for stacked densities.
     */
    function KDE(params) {
      Transform.call(this, null, params);
    }
  
    KDE.Definition = {
      "type": "KDE",
      "metadata": {"generates": true},
      "params": [
        { "name": "groupby", "type": "field", "array": true },
        { "name": "field", "type": "field", "required": true },
        { "name": "cumulative", "type": "boolean", "default": false },
        { "name": "counts", "type": "boolean", "default": false },
        { "name": "bandwidth", "type": "number", "default": 0 },
        { "name": "extent", "type": "number", "array": true, "length": 2 },
        { "name": "steps", "type": "number" },
        { "name": "minsteps", "type": "number", "default": 25 },
        { "name": "maxsteps", "type": "number", "default": 200 },
        { "name": "as", "type": "string", "array": true, "default": ["value", "density"] }
      ]
    };
  
    var prototype$o = inherits(KDE, Transform);
  
    prototype$o.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);
  
      if (!this.value || pulse.changed() || _.modified()) {
        const source = pulse.materialize(pulse.SOURCE).source,
              groups = partition$1(source, _.groupby, _.field),
              names = (_.groupby || []).map(accessorName),
              bandwidth = _.bandwidth,
              method = _.cumulative ? 'cdf' : 'pdf',
              minsteps = _.steps || _.minsteps || 25,
              maxsteps = _.steps || _.maxsteps || 200,
              as = _.as || ['value', 'density'],
              values = [];
  
        if (method !== 'pdf' && method !== 'cdf') {
          error('Invalid density method: ' + method);
        }
  
        groups.forEach(g => {
          const density = randomKDE(g, bandwidth)[method],
                scale = _.counts ? g.length : 1,
                domain = _.extent || d3Array.extent(g);
  
          sampleCurve(density, domain, minsteps, maxsteps).forEach(v => {
            const t = {};
            for (let i=0; i<names.length; ++i) {
              t[names[i]] = g.dims[i];
            }
            t[as[0]] = v[0];
            t[as[1]] = v[1] * scale;
            values.push(ingest(t));
          });
        });
  
        if (this.value) out.rem = this.value;
        this.value = out.add = out.source = values;
      }
  
      return out;
    };
  
    function partition$1(data, groupby, field) {
      var groups = [],
          get = function(f) { return f(t); },
          map, i, n, t, k, g;
  
      // partition data points into stack groups
      if (groupby == null) {
        groups.push(data.map(field));
      } else {
        for (map={}, i=0, n=data.length; i<n; ++i) {
          t = data[i];
          k = groupby.map(get);
          g = map[k];
          if (!g) {
            map[k] = (g = []);
            g.dims = k;
            groups.push(g);
          }
          g.push(field(t));
        }
      }
  
      return groups;
    }
  
    /**
     * Generates a key function.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<string>} params.fields - The field name(s) for the key function.
     * @param {boolean} params.flat - A boolean flag indicating if the field names
     *  should be treated as flat property names, side-stepping nested field
     *  lookups normally indicated by dot or bracket notation.
     */
    function Key(params) {
      Operator.call(this, null, update$4, params);
    }
  
    inherits(Key, Operator);
  
    function update$4(_) {
      return (this.value && !_.modified()) ? this.value : key(_.fields, _.flat);
    }
  
    /**
     * Load and parse data from an external source. Marshalls parameter
     * values and then invokes the Dataflow request method.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {string} params.url - The URL to load from.
     * @param {object} params.format - The data format options.
     */
    function Load(params) {
      Transform.call(this, [], params);
    }
  
    var prototype$p = inherits(Load, Transform);
  
    prototype$p.transform = function(_, pulse) {
      const df = pulse.dataflow;
  
      if (_.values) {
        // parse and ingest values
        return output$1(this, pulse, df.parse(_.values, _.format));
      } else {
        // return promise for async loading
        return df.request(_.url, _.format)
          .then(res => output$1(this, pulse, res.data || []));
      }
    };
  
    function output$1(op, pulse, data) {
      data.forEach(ingest);
      const out = pulse.fork(pulse.NO_FIELDS & pulse.NO_SOURCE);
      out.rem = op.value;
      op.value = out.add = out.source = data;
      return out;
    }
  
    /**
     * Extend tuples by joining them with values from a lookup table.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Map} params.index - The lookup table map.
     * @param {Array<function(object): *} params.fields - The fields to lookup.
     * @param {Array<string>} params.as - Output field names for each lookup value.
     * @param {*} [params.default] - A default value to use if lookup fails.
     */
    function Lookup(params) {
      Transform.call(this, {}, params);
    }
  
    Lookup.Definition = {
      "type": "Lookup",
      "metadata": {"modifies": true},
      "params": [
        { "name": "index", "type": "index", "params": [
            {"name": "from", "type": "data", "required": true },
            {"name": "key", "type": "field", "required": true }
          ] },
        { "name": "values", "type": "field", "array": true },
        { "name": "fields", "type": "field", "array": true, "required": true },
        { "name": "as", "type": "string", "array": true },
        { "name": "default", "default": null }
      ]
    };
  
    var prototype$q = inherits(Lookup, Transform);
  
    prototype$q.transform = function(_, pulse) {
      var out = pulse,
          as = _.as,
          keys = _.fields,
          index = _.index,
          values = _.values,
          defaultValue = _.default==null ? null : _.default,
          reset = _.modified(),
          flag = reset ? pulse.SOURCE : pulse.ADD,
          n = keys.length,
          set, m, mods;
  
      if (values) {
        m = values.length;
  
        if (n > 1 && !as) {
          error('Multi-field lookup requires explicit "as" parameter.');
        }
        if (as && as.length !== n * m) {
          error('The "as" parameter has too few output field names.');
        }
        as = as || values.map(accessorName);
  
        set = function(t) {
          for (var i=0, k=0, j, v; i<n; ++i) {
            v = index.get(keys[i](t));
            if (v == null) for (j=0; j<m; ++j, ++k) t[as[k]] = defaultValue;
            else for (j=0; j<m; ++j, ++k) t[as[k]] = values[j](v);
          }
        };
      } else {
        if (!as) {
          error('Missing output field names.');
        }
  
        set = function(t) {
          for (var i=0, v; i<n; ++i) {
            v = index.get(keys[i](t));
            t[as[i]] = v==null ? defaultValue : v;
          }
        };
      }
  
      if (reset) {
        out = pulse.reflow(true);
      } else {
        mods = keys.some(function(k) { return pulse.modified(k.fields); });
        flag |= (mods ? pulse.MOD : 0);
      }
      pulse.visit(flag, set);
  
      return out.modifies(as);
    };
  
    /**
     * Computes global min/max extents over a collection of extents.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<Array<number>>} params.extents - The input extents.
     */
    function MultiExtent(params) {
      Operator.call(this, null, update$5, params);
    }
  
    inherits(MultiExtent, Operator);
  
    function update$5(_) {
      if (this.value && !_.modified()) {
        return this.value;
      }
  
      var min = +Infinity,
          max = -Infinity,
          ext = _.extents,
          i, n, e;
  
      for (i=0, n=ext.length; i<n; ++i) {
        e = ext[i];
        if (e[0] < min) min = e[0];
        if (e[1] > max) max = e[1];
      }
      return [min, max];
    }
  
    /**
     * Merge a collection of value arrays.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<Array<*>>} params.values - The input value arrrays.
     */
    function MultiValues(params) {
      Operator.call(this, null, update$6, params);
    }
  
    inherits(MultiValues, Operator);
  
    function update$6(_) {
      return (this.value && !_.modified())
        ? this.value
        : _.values.reduce(function(data, _) { return data.concat(_); }, []);
    }
  
    /**
     * Operator whose value is simply its parameter hash. This operator is
     * useful for enabling reactive updates to values of nested objects.
     * @constructor
     * @param {object} params - The parameters for this operator.
     */
    function Params(params) {
      Transform.call(this, null, params);
    }
  
    inherits(Params, Transform);
  
    Params.prototype.transform = function(_, pulse) {
      this.modified(_.modified());
      this.value = _;
      return pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS); // do not pass tuples
    };
  
    /**
     * Aggregate and pivot selected field values to become new fields.
     * This operator is useful to construction cross-tabulations.
     * @constructor
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors
     *  to groupby. These fields act just like groupby fields of an Aggregate transform.
     * @param {function(object): *} params.field - The field to pivot on. The unique
     *  values of this field become new field names in the output stream.
     * @param {function(object): *} params.value - The field to populate pivoted fields.
     *  The aggregate values of this field become the values of the new pivoted fields.
     * @param {string} [params.op] - The aggregation operation for the value field,
     *  applied per cell in the output stream. The default is "sum".
     * @param {number} [params.limit] - An optional parameter indicating the maximum
     *  number of pivoted fields to generate. The pivoted field names are sorted in
     *  ascending order prior to enforcing the limit.
     */
    function Pivot(params) {
      Aggregate.call(this, params);
    }
  
    Pivot.Definition = {
      "type": "Pivot",
      "metadata": {"generates": true, "changes": true},
      "params": [
        { "name": "groupby", "type": "field", "array": true },
        { "name": "field", "type": "field", "required": true },
        { "name": "value", "type": "field", "required": true },
        { "name": "op", "type": "enum", "values": ValidAggregateOps, "default": "sum" },
        { "name": "limit", "type": "number", "default": 0 },
        { "name": "key", "type": "field" }
      ]
    };
  
    var prototype$r = inherits(Pivot, Aggregate);
  
    prototype$r._transform = prototype$r.transform;
  
    prototype$r.transform = function(_, pulse) {
      return this._transform(aggregateParams(_, pulse), pulse);
    };
  
    // Shoehorn a pivot transform into an aggregate transform!
    // First collect all unique pivot field values.
    // Then generate aggregate fields for each output pivot field.
    function aggregateParams(_, pulse) {
      var key    = _.field,
      value  = _.value,
          op     = (_.op === 'count' ? '__count__' : _.op) || 'sum',
          fields = accessorFields(key).concat(accessorFields(value)),
          keys   = pivotKeys(key, _.limit || 0, pulse);
  
      return {
        key:      _.key,
        groupby:  _.groupby,
        ops:      keys.map(function() { return op; }),
        fields:   keys.map(function(k) { return get(k, key, value, fields); }),
        as:       keys.map(function(k) { return k + ''; }),
        modified: _.modified.bind(_)
      };
    }
  
    // Generate aggregate field accessor.
    // Output NaN for non-existent values; aggregator will ignore!
    function get(k, key, value, fields) {
      return accessor(
        function(d) { return key(d) === k ? value(d) : NaN; },
        fields,
        k + ''
      );
    }
  
    // Collect (and optionally limit) all unique pivot values.
    function pivotKeys(key, limit, pulse) {
      var map = {},
          list = [];
  
      pulse.visit(pulse.SOURCE, function(t) {
        var k = key(t);
        if (!map[k]) {
          map[k] = 1;
          list.push(k);
        }
      });
  
      // TODO? Move this comparator to vega-util?
      list.sort(function(u, v) {
        return (u<v||u==null) && v!=null ? -1
          : (u>v||v==null) && u!=null ? 1
          : ((v=v instanceof Date?+v:v),(u=u instanceof Date?+u:u))!==u && v===v ? -1
          : v!==v && u===u ? 1 : 0;
      });
  
      return limit ? list.slice(0, limit) : list;
    }
  
    /**
     * Partitions pre-faceted data into tuple subflows.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(Dataflow, string): Operator} params.subflow - A function
     *   that generates a subflow of operators and returns its root operator.
     * @param {function(object): Array<object>} params.field - The field
     *   accessor for an array of subflow tuple objects.
     */
    function PreFacet(params) {
      Facet.call(this, params);
    }
  
    var prototype$s = inherits(PreFacet, Facet);
  
    prototype$s.transform = function(_, pulse) {
      var self = this,
          flow = _.subflow,
          field = _.field;
  
      if (_.modified('field') || field && pulse.modified(accessorFields(field))) {
        error('PreFacet does not support field modification.');
      }
  
      this._targets.active = 0; // reset list of active subflows
  
      pulse.visit(pulse.MOD, function(t) {
        var sf = self.subflow(tupleid(t), flow, pulse, t);
        field ? field(t).forEach(function(_) { sf.mod(_); }) : sf.mod(t);
      });
  
      pulse.visit(pulse.ADD, function(t) {
        var sf = self.subflow(tupleid(t), flow, pulse, t);
        field ? field(t).forEach(function(_) { sf.add(ingest(_)); }) : sf.add(t);
      });
  
      pulse.visit(pulse.REM, function(t) {
        var sf = self.subflow(tupleid(t), flow, pulse, t);
        field ? field(t).forEach(function(_) { sf.rem(_); }) : sf.rem(t);
      });
  
      return pulse;
    };
  
    /**
     * Performs a relational projection, copying selected fields from source
     * tuples to a new set of derived tuples.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<function(object): *} params.fields - The fields to project,
     *   as an array of field accessors. If unspecified, all fields will be
     *   copied with names unchanged.
     * @param {Array<string>} [params.as] - Output field names for each projected
     *   field. Any unspecified fields will use the field name provided by
     *   the field accessor.
     */
    function Project(params) {
      Transform.call(this, null, params);
    }
  
    Project.Definition = {
      "type": "Project",
      "metadata": {"generates": true, "changes": true},
      "params": [
        { "name": "fields", "type": "field", "array": true },
        { "name": "as", "type": "string", "null": true, "array": true },
      ]
    };
  
    var prototype$t = inherits(Project, Transform);
  
    prototype$t.transform = function(_, pulse) {
      var fields = _.fields,
          as = fieldNames(_.fields, _.as || []),
          derive = fields
            ? function(s, t) { return project(s, t, fields, as); }
            : rederive,
          out, lut;
  
      if (this.value) {
        lut = this.value;
      } else {
        pulse = pulse.addAll();
        lut = this.value = {};
      }
  
      out = pulse.fork(pulse.NO_SOURCE);
  
      pulse.visit(pulse.REM, function(t) {
        var id = tupleid(t);
        out.rem.push(lut[id]);
        lut[id] = null;
      });
  
      pulse.visit(pulse.ADD, function(t) {
        var dt = derive(t, ingest({}));
        lut[tupleid(t)] = dt;
        out.add.push(dt);
      });
  
      pulse.visit(pulse.MOD, function(t) {
        out.mod.push(derive(t, lut[tupleid(t)]));
      });
  
      return out;
    };
  
    function project(s, t, fields, as) {
      for (var i=0, n=fields.length; i<n; ++i) {
        t[as[i]] = fields[i](s);
      }
      return t;
    }
  
    /**
     * Proxy the value of another operator as a pure signal value.
     * Ensures no tuples are propagated.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {*} params.value - The value to proxy, becomes the value of this operator.
     */
    function Proxy(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$u = inherits(Proxy, Transform);
  
    prototype$u.transform = function(_, pulse) {
      this.value = _.value;
      return _.modified('value')
        ? pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS)
        : pulse.StopPropagation;
    };
  
    /**
     * Relays a data stream between data processing pipelines.
     * If the derive parameter is set, this transform will create derived
     * copies of observed tuples. This provides derived data streams in which
     * modifications to the tuples do not pollute an upstream data source.
     * @param {object} params - The parameters for this operator.
     * @param {number} [params.derive=false] - Boolean flag indicating if
     *   the transform should make derived copies of incoming tuples.
     * @constructor
     */
    function Relay(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$v = inherits(Relay, Transform);
  
    prototype$v.transform = function(_, pulse) {
      var out, lut;
  
      if (this.value) {
        lut = this.value;
      } else {
        out = pulse = pulse.addAll();
        lut = this.value = {};
      }
  
      if (_.derive) {
        out = pulse.fork(pulse.NO_SOURCE);
  
        pulse.visit(pulse.REM, function(t) {
          var id = tupleid(t);
          out.rem.push(lut[id]);
          lut[id] = null;
        });
  
        pulse.visit(pulse.ADD, function(t) {
          var dt = derive(t);
          lut[tupleid(t)] = dt;
          out.add.push(dt);
        });
  
        pulse.visit(pulse.MOD, function(t) {
          out.mod.push(rederive(t, lut[tupleid(t)]));
        });
      }
  
      return out;
    };
  
    /**
     * Samples tuples passing through this operator.
     * Uses reservoir sampling to maintain a representative sample.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {number} [params.size=1000] - The maximum number of samples.
     */
    function Sample(params) {
      Transform.call(this, [], params);
      this.count = 0;
    }
  
    Sample.Definition = {
      "type": "Sample",
      "metadata": {},
      "params": [
        { "name": "size", "type": "number", "default": 1000 }
      ]
    };
  
    var prototype$w = inherits(Sample, Transform);
  
    prototype$w.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE),
          mod = _.modified('size'),
          num = _.size,
          res = this.value,
          cnt = this.count,
          cap = 0,
          map = res.reduce(function(m, t) {
            m[tupleid(t)] = 1;
            return m;
          }, {});
  
      // sample reservoir update function
      function update(t) {
        var p, idx;
  
        if (res.length < num) {
          res.push(t);
        } else {
          idx = ~~((cnt + 1) * exports.random());
          if (idx < res.length && idx >= cap) {
            p = res[idx];
            if (map[tupleid(p)]) out.rem.push(p); // eviction
            res[idx] = t;
          }
        }
        ++cnt;
      }
  
      if (pulse.rem.length) {
        // find all tuples that should be removed, add to output
        pulse.visit(pulse.REM, function(t) {
          var id = tupleid(t);
          if (map[id]) {
            map[id] = -1;
            out.rem.push(t);
          }
          --cnt;
        });
  
        // filter removed tuples out of the sample reservoir
        res = res.filter(function(t) { return map[tupleid(t)] !== -1; });
      }
  
      if ((pulse.rem.length || mod) && res.length < num && pulse.source) {
        // replenish sample if backing data source is available
        cap = cnt = res.length;
        pulse.visit(pulse.SOURCE, function(t) {
          // update, but skip previously sampled tuples
          if (!map[tupleid(t)]) update(t);
        });
        cap = -1;
      }
  
      if (mod && res.length > num) {
        for (var i=0, n=res.length-num; i<n; ++i) {
          map[tupleid(res[i])] = -1;
          out.rem.push(res[i]);
        }
        res = res.slice(n);
      }
  
      if (pulse.mod.length) {
        // propagate modified tuples in the sample reservoir
        pulse.visit(pulse.MOD, function(t) {
          if (map[tupleid(t)]) out.mod.push(t);
        });
      }
  
      if (pulse.add.length) {
        // update sample reservoir
        pulse.visit(pulse.ADD, update);
      }
  
      if (pulse.add.length || cap < 0) {
        // output newly added tuples
        out.add = res.filter(function(t) { return !map[tupleid(t)]; });
      }
  
      this.count = cnt;
      this.value = out.source = res;
      return out;
    };
  
    /**
     * Generates data tuples for a specified sequence range of numbers.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {number} params.start - The first number in the sequence.
     * @param {number} params.stop - The last number (exclusive) in the sequence.
     * @param {number} [params.step=1] - The step size between numbers in the sequence.
     */
    function Sequence(params) {
      Transform.call(this, null, params);
    }
  
    Sequence.Definition = {
      "type": "Sequence",
      "metadata": {"changes": true},
      "params": [
        { "name": "start", "type": "number", "required": true },
        { "name": "stop", "type": "number", "required": true },
        { "name": "step", "type": "number", "default": 1 },
        { "name": "as", "type": "string", "default": "data" }
      ]
    };
  
    var prototype$x = inherits(Sequence, Transform);
  
    prototype$x.transform = function(_, pulse) {
      if (this.value && !_.modified()) return;
  
      var out = pulse.materialize().fork(pulse.MOD),
          as = _.as || 'data';
  
      out.rem = this.value ? pulse.rem.concat(this.value) : pulse.rem;
  
      this.value = d3Array.range(_.start, _.stop, _.step || 1).map(function(v) {
        var t = {};
        t[as] = v;
        return ingest(t);
      });
  
      out.add = pulse.add.concat(this.value);
  
      return out;
    };
  
    /**
     * Propagates a new pulse without any tuples so long as the input
     * pulse contains some added, removed or modified tuples.
     * @param {object} params - The parameters for this operator.
     * @constructor
     */
    function Sieve(params) {
      Transform.call(this, null, params);
      this.modified(true); // always treat as modified
    }
  
    var prototype$y = inherits(Sieve, Transform);
  
    prototype$y.transform = function(_, pulse) {
      this.value = pulse.source;
      return pulse.changed()
        ? pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS)
        : pulse.StopPropagation;
    };
  
    /**
     * An index that maps from unique, string-coerced, field values to tuples.
     * Assumes that the field serves as a unique key with no duplicate values.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The field accessor to index.
     */
    function TupleIndex(params) {
      Transform.call(this, fastmap(), params);
    }
  
    var prototype$z = inherits(TupleIndex, Transform);
  
    prototype$z.transform = function(_, pulse) {
      var df = pulse.dataflow,
          field = _.field,
          index = this.value,
          mod = true;
  
      function set(t) { index.set(field(t), t); }
  
      if (_.modified('field') || pulse.modified(field.fields)) {
        index.clear();
        pulse.visit(pulse.SOURCE, set);
      } else if (pulse.changed()) {
        pulse.visit(pulse.REM, function(t) { index.delete(field(t)); });
        pulse.visit(pulse.ADD, set);
      } else {
        mod = false;
      }
  
      this.modified(mod);
      if (index.empty > df.cleanThreshold) df.runAfter(index.clean);
      return pulse.fork();
    };
  
    /**
     * Extracts an array of values. Assumes the source data has already been
     * reduced as needed (e.g., by an upstream Aggregate transform).
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The domain field to extract.
     * @param {function(*,*): number} [params.sort] - An optional
     *   comparator function for sorting the values. The comparator will be
     *   applied to backing tuples prior to value extraction.
     */
    function Values(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$A = inherits(Values, Transform);
  
    prototype$A.transform = function(_, pulse) {
      var run = !this.value
        || _.modified('field')
        || _.modified('sort')
        || pulse.changed()
        || (_.sort && pulse.modified(_.sort.fields));
  
      if (run) {
        this.value = (_.sort
          ? pulse.source.slice().sort(_.sort)
          : pulse.source).map(_.field);
      }
    };
  
    function WindowOp(op, field, param, as) {
      let fn = WindowOps[op](field, param);
      return {
        init:   fn.init || zero,
        update: function(w, t) { t[as] = fn.next(w); }
      };
    }
  
    const WindowOps = {
      row_number: function() {
        return {
          next: w => w.index + 1
        };
      },
      rank: function() {
        let rank;
        return {
          init: () => rank = 1,
          next: w => {
            let i = w.index,
                data = w.data;
            return (i && w.compare(data[i - 1], data[i])) ? (rank = i + 1) : rank;
          }
        };
      },
      dense_rank: function() {
        let drank;
        return {
          init: () => drank = 1,
          next: w => {
            let i = w.index,
                d = w.data;
            return (i && w.compare(d[i - 1], d[i])) ? ++drank : drank;
          }
        };
      },
      percent_rank: function() {
        let rank = WindowOps.rank(),
            next = rank.next;
        return {
          init: rank.init,
          next: w => (next(w) - 1) / (w.data.length - 1)
        };
      },
      cume_dist: function() {
        let cume;
        return {
          init: () => cume = 0,
          next: w => {
            let i = w.index,
                d = w.data,
                c = w.compare;
            if (cume < i) {
              while (i + 1 < d.length && !c(d[i], d[i + 1])) ++i;
              cume = i;
            }
            return (1 + cume) / d.length;
          }
        };
      },
      ntile: function(field, num) {
        num = +num;
        if (!(num > 0)) error('ntile num must be greater than zero.');
        let cume = WindowOps.cume_dist(),
            next = cume.next;
        return {
          init: cume.init,
          next: w => Math.ceil(num * next(w))
        };
      },
  
      lag: function(field, offset) {
        offset = +offset || 1;
        return {
          next: w => {
            let i = w.index - offset;
            return i >= 0 ? field(w.data[i]) : null;
          }
        };
      },
      lead: function(field, offset) {
        offset = +offset || 1;
        return {
          next: w => {
            let i = w.index + offset,
                d = w.data;
            return i < d.length ? field(d[i]) : null;
          }
        };
      },
  
      first_value: function(field) {
        return {
          next: w => field(w.data[w.i0])
        };
      },
      last_value: function(field) {
        return {
          next: w => field(w.data[w.i1 - 1])
        }
      },
      nth_value: function(field, nth) {
        nth = +nth;
        if (!(nth > 0)) error('nth_value nth must be greater than zero.');
        return {
          next: w => {
            let i = w.i0 + (nth - 1);
            return i < w.i1 ? field(w.data[i]) : null;
          }
        }
      },
  
      prev_value: function(field) {
        let prev = null;
        return {
          next: w => {
            let v = field(w.data[w.index]);
            return v != null ? (prev = v) : prev;
          }
        }
      },
      next_value: function(field) {
        let v = null,
            i = -1;
        return {
          next: w => {
            let d = w.data;
            return w.index <= i ? v
              : (i = find(field, d, w.index)) < 0
                ? (i = d.length, v = null)
                : (v = field(d[i]));
          }
        };
      },
  
    };
  
    function find(field, data, index) {
      for (let n = data.length; index < n; ++index) {
        let v = field(data[index]);
        if (v != null) return index;
      }
      return -1;
    }
  
    var ValidWindowOps = Object.keys(WindowOps);
  
    function WindowState(_) {
      let self = this,
          ops = array(_.ops),
          fields = array(_.fields),
          params = array(_.params),
          as = array(_.as),
          outputs = self.outputs = [],
          windows = self.windows = [],
          inputs = {},
          map = {},
          countOnly = true,
          counts = [],
          measures = [];
  
      function visitInputs(f) {
        array(accessorFields(f)).forEach(_ => inputs[_] = 1);
      }
      visitInputs(_.sort);
  
      ops.forEach(function(op, i) {
        let field = fields[i],
            mname = accessorName(field),
            name = measureName(op, mname, as[i]);
  
        visitInputs(field);
        outputs.push(name);
  
        // Window operation
        if (WindowOps.hasOwnProperty(op)) {
          windows.push(WindowOp(op, fields[i], params[i], name));
        }
  
        // Aggregate operation
        else {
          if (field == null && op !== 'count') {
            error('Null aggregate field specified.');
          }
          if (op === 'count') {
            counts.push(name);
            return;
          }
  
          countOnly = false;
          let m = map[mname];
          if (!m) {
            m = (map[mname] = []);
            m.field = field;
            measures.push(m);
          }
          m.push(createMeasure(op, name));
        }
      });
  
      if (counts.length || measures.length) {
        self.cell = cell(measures, counts, countOnly);
      }
  
      self.inputs = Object.keys(inputs);
    }
  
    const prototype$B = WindowState.prototype;
  
    prototype$B.init = function() {
      this.windows.forEach(_ => _.init());
      if (this.cell) this.cell.init();
    };
  
    prototype$B.update = function(w, t) {
      let self = this,
          cell = self.cell,
          wind = self.windows,
          data = w.data,
          m = wind && wind.length,
          j;
  
      if (cell) {
        for (j=w.p0; j<w.i0; ++j) cell.rem(data[j]);
        for (j=w.p1; j<w.i1; ++j) cell.add(data[j]);
        cell.set(t);
      }
      for (j=0; j<m; ++j) wind[j].update(w, t);
    };
  
    function cell(measures, counts, countOnly) {
      measures = measures.map(m => compileMeasures(m, m.field));
  
      let cell = {
        num:   0,
        agg:   null,
        store: false,
        count: counts
      };
  
      if (!countOnly) {
        var n = measures.length,
            a = cell.agg = Array(n),
            i = 0;
        for (; i<n; ++i) a[i] = new measures[i](cell);
      }
  
      if (cell.store) {
        var store = cell.data = new TupleStore();
      }
  
      cell.add = function(t) {
        cell.num += 1;
        if (countOnly) return;
        if (store) store.add(t);
        for (let i=0; i<n; ++i) {
          a[i].add(a[i].get(t), t);
        }
      };
  
      cell.rem = function(t) {
        cell.num -= 1;
        if (countOnly) return;
        if (store) store.rem(t);
        for (let i=0; i<n; ++i) {
          a[i].rem(a[i].get(t), t);
        }
      };
  
      cell.set = function(t) {
        let i, n;
  
        // consolidate stored values
        if (store) store.values();
  
        // update tuple properties
        for (i=0, n=counts.length; i<n; ++i) t[counts[i]] = cell.num;
        if (!countOnly) for (i=0, n=a.length; i<n; ++i) a[i].set(t);
      };
  
      cell.init = function() {
        cell.num = 0;
        if (store) store.reset();
        for (let i=0; i<n; ++i) a[i].init();
      };
  
      return cell;
    }
  
    /**
     * Perform window calculations and write results to the input stream.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(*,*): number} [params.sort] - A comparator function for sorting tuples within a window.
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors by which to partition tuples into separate windows.
     * @param {Array<string>} params.ops - An array of strings indicating window operations to perform.
     * @param {Array<function(object): *>} [params.fields] - An array of accessors
     *   for data fields to use as inputs to window operations.
     * @param {Array<*>} [params.params] - An array of parameter values for window operations.
     * @param {Array<string>} [params.as] - An array of output field names for window operations.
     * @param {Array<number>} [params.frame] - Window frame definition as two-element array.
     * @param {boolean} [params.ignorePeers=false] - If true, base window frame boundaries on row
     *   number alone, ignoring peers with identical sort values. If false (default),
     *   the window boundaries will be adjusted to include peer values.
     */
    function Window(params) {
      Transform.call(this, {}, params);
      this._mlen = 0;
      this._mods = [];
    }
  
    Window.Definition = {
      "type": "Window",
      "metadata": {"modifies": true},
      "params": [
        { "name": "sort", "type": "compare" },
        { "name": "groupby", "type": "field", "array": true },
        { "name": "ops", "type": "enum", "array": true, "values": ValidWindowOps.concat(ValidAggregateOps) },
        { "name": "params", "type": "number", "null": true, "array": true },
        { "name": "fields", "type": "field", "null": true, "array": true },
        { "name": "as", "type": "string", "null": true, "array": true },
        { "name": "frame", "type": "number", "null": true, "array": true, "length": 2, "default": [null, 0] },
        { "name": "ignorePeers", "type": "boolean", "default": false }
      ]
    };
  
    var prototype$C = inherits(Window, Transform);
  
    prototype$C.transform = function(_, pulse) {
      var self = this,
          state = self.state,
          mod = _.modified(),
          i, n;
  
      this.stamp = pulse.stamp;
  
      // initialize window state
      if (!state || mod) {
        state = self.state = new WindowState(_);
      }
  
      // retrieve group for a tuple
      var key = groupkey(_.groupby);
      function group(t) { return self.group(key(t)); }
  
      // partition input tuples
      if (mod || pulse.modified(state.inputs)) {
        self.value = {};
        pulse.visit(pulse.SOURCE, function(t) { group(t).add(t); });
      } else {
        pulse.visit(pulse.REM, function(t) { group(t).remove(t); });
        pulse.visit(pulse.ADD, function(t) { group(t).add(t); });
      }
  
      // perform window calculations for each modified partition
      for (i=0, n=self._mlen; i<n; ++i) {
        processPartition(self._mods[i], state, _);
      }
      self._mlen = 0;
      self._mods = [];
  
      // TODO don't reflow everything?
      return pulse.reflow(mod).modifies(state.outputs);
    };
  
    prototype$C.group = function(key) {
      var self = this,
          group = self.value[key];
  
      if (!group) {
        group = self.value[key] = SortedList(tupleid);
        group.stamp = -1;
      }
  
      if (group.stamp < self.stamp) {
        group.stamp = self.stamp;
        self._mods[self._mlen++] = group;
      }
  
      return group;
    };
  
    function processPartition(list, state, _) {
      var sort = _.sort,
          range = sort && !_.ignorePeers,
          frame = _.frame || [null, 0],
          data = list.data(sort),
          n = data.length,
          i = 0,
          b = range ? d3Array.bisector(sort) : null,
          w = {
            i0: 0, i1: 0, p0: 0, p1: 0, index: 0,
            data: data, compare: sort || constant(-1)
          };
  
      for (state.init(); i<n; ++i) {
        setWindow(w, frame, i, n);
        if (range) adjustRange(w, b);
        state.update(w, data[i]);
      }
    }
  
    function setWindow(w, f, i, n) {
      w.p0 = w.i0;
      w.p1 = w.i1;
      w.i0 = f[0] == null ? 0 : Math.max(0, i - Math.abs(f[0]));
      w.i1 = f[1] == null ? n : Math.min(n, i + Math.abs(f[1]) + 1);
      w.index = i;
    }
  
    // if frame type is 'range', adjust window for peer values
    function adjustRange(w, bisect) {
      var r0 = w.i0,
          r1 = w.i1 - 1,
          c = w.compare,
          d = w.data,
          n = d.length - 1;
  
      if (r0 > 0 && !c(d[r0], d[r0-1])) w.i0 = bisect.left(d, d[r0]);
      if (r1 < n && !c(d[r1], d[r1+1])) w.i1 = bisect.right(d, d[r1]);
    }
  
  
  
    var tx = /*#__PURE__*/Object.freeze({
      aggregate: Aggregate,
      bin: Bin,
      collect: Collect,
      compare: Compare,
      countpattern: CountPattern,
      cross: Cross,
      density: Density,
      expression: Expression,
      extent: Extent,
      facet: Facet,
      field: Field,
      filter: Filter,
      flatten: Flatten,
      fold: Fold,
      formula: Formula,
      generate: Generate,
      impute: Impute,
      joinaggregate: JoinAggregate,
      kde: KDE,
      key: Key,
      load: Load,
      lookup: Lookup,
      multiextent: MultiExtent,
      multivalues: MultiValues,
      params: Params,
      pivot: Pivot,
      prefacet: PreFacet,
      project: Project,
      proxy: Proxy,
      relay: Relay,
      sample: Sample,
      sequence: Sequence,
      sieve: Sieve,
      subflow: Subflow,
      tupleindex: TupleIndex,
      values: Values,
      window: Window
    });
  
    const Top = 'top';
    const Left = 'left';
    const Right = 'right';
    const Bottom = 'bottom';
  
    const TopLeft = 'top-left';
    const TopRight = 'top-right';
    const BottomLeft = 'bottom-left';
    const BottomRight = 'bottom-right';
  
    const Start = 'start';
    const Middle = 'middle';
    const End = 'end';
  
    const X = 'x';
    const Y = 'y';
  
    const Group = 'group';
  
    const AxisRole = 'axis';
    const TitleRole = 'title';
    const FrameRole = 'frame';
    const ScopeRole = 'scope';
    const LegendRole = 'legend';
  
    const RowHeader = 'row-header';
    const RowFooter = 'row-footer';
    const RowTitle  = 'row-title';
    const ColHeader = 'column-header';
    const ColFooter = 'column-footer';
    const ColTitle  = 'column-title';
  
    const Padding = 'padding';
  
    const Symbols = 'symbol';
  
    const Fit  = 'fit';
    const FitX = 'fit-x';
    const FitY = 'fit-y';
    const Pad  = 'pad';
    const None$1 = 'none';
  
    const All = 'all';
    const Each = 'each';
    const Flush = 'flush';
  
    const Column = 'column';
    const Row = 'row';
  
    function Bounds(b) {
      this.clear();
      if (b) this.union(b);
    }
  
    var prototype$D = Bounds.prototype;
  
    prototype$D.clone = function() {
      return new Bounds(this);
    };
  
    prototype$D.clear = function() {
      this.x1 = +Number.MAX_VALUE;
      this.y1 = +Number.MAX_VALUE;
      this.x2 = -Number.MAX_VALUE;
      this.y2 = -Number.MAX_VALUE;
      return this;
    };
  
    prototype$D.empty = function() {
      return (
        this.x1 === +Number.MAX_VALUE &&
        this.y1 === +Number.MAX_VALUE &&
        this.x2 === -Number.MAX_VALUE &&
        this.y2 === -Number.MAX_VALUE
      );
    };
  
    prototype$D.equals = function(b) {
      return (
        this.x1 === b.x1 &&
        this.y1 === b.y1 &&
        this.x2 === b.x2 &&
        this.y2 === b.y2
      );
    };
  
    prototype$D.set = function(x1, y1, x2, y2) {
      if (x2 < x1) {
        this.x2 = x1;
        this.x1 = x2;
      } else {
        this.x1 = x1;
        this.x2 = x2;
      }
      if (y2 < y1) {
        this.y2 = y1;
        this.y1 = y2;
      } else {
        this.y1 = y1;
        this.y2 = y2;
      }
      return this;
    };
  
    prototype$D.add = function(x, y) {
      if (x < this.x1) this.x1 = x;
      if (y < this.y1) this.y1 = y;
      if (x > this.x2) this.x2 = x;
      if (y > this.y2) this.y2 = y;
      return this;
    };
  
    prototype$D.expand = function(d) {
      this.x1 -= d;
      this.y1 -= d;
      this.x2 += d;
      this.y2 += d;
      return this;
    };
  
    prototype$D.round = function() {
      this.x1 = Math.floor(this.x1);
      this.y1 = Math.floor(this.y1);
      this.x2 = Math.ceil(this.x2);
      this.y2 = Math.ceil(this.y2);
      return this;
    };
  
    prototype$D.translate = function(dx, dy) {
      this.x1 += dx;
      this.x2 += dx;
      this.y1 += dy;
      this.y2 += dy;
      return this;
    };
  
    prototype$D.rotate = function(angle, x, y) {
      const p = this.rotatedPoints(angle, x, y);
      return this.clear()
        .add(p[0], p[1])
        .add(p[2], p[3])
        .add(p[4], p[5])
        .add(p[6], p[7]);
    };
  
    prototype$D.rotatedPoints = function(angle, x, y) {
      var {x1, y1, x2, y2} = this,
          cos = Math.cos(angle),
          sin = Math.sin(angle),
          cx = x - x*cos + y*sin,
          cy = y - x*sin - y*cos;
  
      return [
        cos*x1 - sin*y1 + cx, sin*x1 + cos*y1 + cy,
        cos*x1 - sin*y2 + cx, sin*x1 + cos*y2 + cy,
        cos*x2 - sin*y1 + cx, sin*x2 + cos*y1 + cy,
        cos*x2 - sin*y2 + cx, sin*x2 + cos*y2 + cy
      ];
    };
  
    prototype$D.union = function(b) {
      if (b.x1 < this.x1) this.x1 = b.x1;
      if (b.y1 < this.y1) this.y1 = b.y1;
      if (b.x2 > this.x2) this.x2 = b.x2;
      if (b.y2 > this.y2) this.y2 = b.y2;
      return this;
    };
  
    prototype$D.intersect = function(b) {
      if (b.x1 > this.x1) this.x1 = b.x1;
      if (b.y1 > this.y1) this.y1 = b.y1;
      if (b.x2 < this.x2) this.x2 = b.x2;
      if (b.y2 < this.y2) this.y2 = b.y2;
      return this;
    };
  
    prototype$D.encloses = function(b) {
      return b && (
        this.x1 <= b.x1 &&
        this.x2 >= b.x2 &&
        this.y1 <= b.y1 &&
        this.y2 >= b.y2
      );
    };
  
    prototype$D.alignsWith = function(b) {
      return b && (
        this.x1 == b.x1 ||
        this.x2 == b.x2 ||
        this.y1 == b.y1 ||
        this.y2 == b.y2
      );
    };
  
    prototype$D.intersects = function(b) {
      return b && !(
        this.x2 < b.x1 ||
        this.x1 > b.x2 ||
        this.y2 < b.y1 ||
        this.y1 > b.y2
      );
    };
  
    prototype$D.contains = function(x, y) {
      return !(
        x < this.x1 ||
        x > this.x2 ||
        y < this.y1 ||
        y > this.y2
      );
    };
  
    prototype$D.width = function() {
      return this.x2 - this.x1;
    };
  
    prototype$D.height = function() {
      return this.y2 - this.y1;
    };
  
    var gradient_id = 0;
  
    const patternPrefix = 'p_';
  
    function isGradient(value) {
      return value && value.gradient;
    }
  
    function gradientRef(g, defs, base) {
      let id = g.id,
          type = g.gradient,
          prefix = type === 'radial' ? patternPrefix : '';
  
      // check id, assign default values as needed
      if (!id) {
        id = g.id = 'gradient_' + (gradient_id++);
        if (type === 'radial') {
          g.x1 = get$1(g.x1, 0.5);
          g.y1 = get$1(g.y1, 0.5);
          g.r1 = get$1(g.r1, 0);
          g.x2 = get$1(g.x2, 0.5);
          g.y2 = get$1(g.y2, 0.5);
          g.r2 = get$1(g.r2, 0.5);
          prefix = patternPrefix;
        } else {
          g.x1 = get$1(g.x1, 0);
          g.y1 = get$1(g.y1, 0);
          g.x2 = get$1(g.x2, 1);
          g.y2 = get$1(g.y2, 0);
        }
      }
  
      // register definition
      defs[id] = g;
  
      // return url reference
      return 'url(' + (base || '') + '#' + prefix + id + ')';
    }
  
    function get$1(val, def) {
      return val != null ? val : def;
    }
  
    function Gradient(p0, p1) {
      var stops = [], gradient;
      return gradient = {
        gradient: 'linear',
        x1: p0 ? p0[0] : 0,
        y1: p0 ? p0[1] : 0,
        x2: p1 ? p1[0] : 1,
        y2: p1 ? p1[1] : 0,
        stops: stops,
        stop: function(offset, color) {
          stops.push({offset: offset, color: color});
          return gradient;
        }
      };
    }
  
    function Item(mark) {
      this.mark = mark;
      this.bounds = (this.bounds || new Bounds());
    }
  
    function GroupItem(mark) {
      Item.call(this, mark);
      this.items = (this.items || []);
    }
  
    inherits(GroupItem, Item);
  
    function domCanvas(w, h) {
      if (typeof document !== 'undefined' && document.createElement) {
        var c = document.createElement('canvas');
        if (c && c.getContext) {
          c.width = w;
          c.height = h;
          return c;
        }
      }
      return null;
    }
  
    function domImage() {
      return typeof Image !== 'undefined' ? Image : null;
    }
  
    function ResourceLoader(customLoader) {
      this._pending = 0;
      this._loader = customLoader || loader();
    }
  
    var prototype$E = ResourceLoader.prototype;
  
    prototype$E.pending = function() {
      return this._pending;
    };
  
    function increment(loader) {
      loader._pending += 1;
    }
  
    function decrement(loader) {
      loader._pending -= 1;
    }
  
    prototype$E.sanitizeURL = function(uri) {
      var loader = this;
      increment(loader);
  
      return loader._loader.sanitize(uri, {context:'href'})
        .then(function(opt) {
          decrement(loader);
          return opt;
        })
        .catch(function() {
          decrement(loader);
          return null;
        });
    };
  
    prototype$E.loadImage = function(uri) {
      var loader = this,
          Image = domImage();
      increment(loader);
  
      return loader._loader
        .sanitize(uri, {context: 'image'})
        .then(function(opt) {
          var url = opt.href;
          if (!url || !Image) throw {url: url};
  
          var img = new Image();
  
          img.onload = function() {
            decrement(loader);
            img.loaded = true;
          };
  
          img.onerror = function() {
            decrement(loader);
            img.loaded = false;
          };
  
          img.src = url;
          return img;
        })
        .catch(function(e) {
          decrement(loader);
          return {loaded: false, width: 0, height: 0, src: e && e.url || ''};
        });
    };
  
    prototype$E.ready = function() {
      var loader = this;
      return new Promise(function(accept) {
        function poll(value) {
          if (!loader.pending()) accept(value);
          else setTimeout(function() { poll(true); }, 10);
        }
        poll(false);
      });
    };
  
    var lookup = {
      'basis': {
        curve: d3Shape.curveBasis
      },
      'basis-closed': {
        curve: d3Shape.curveBasisClosed
      },
      'basis-open': {
        curve: d3Shape.curveBasisOpen
      },
      'bundle': {
        curve: d3Shape.curveBundle,
        tension: 'beta',
        value: 0.85
      },
      'cardinal': {
        curve: d3Shape.curveCardinal,
        tension: 'tension',
        value: 0
      },
      'cardinal-open': {
        curve: d3Shape.curveCardinalOpen,
        tension: 'tension',
        value: 0
      },
      'cardinal-closed': {
        curve: d3Shape.curveCardinalClosed,
        tension: 'tension',
        value: 0
      },
      'catmull-rom': {
        curve: d3Shape.curveCatmullRom,
        tension: 'alpha',
        value: 0.5
      },
      'catmull-rom-closed': {
        curve: d3Shape.curveCatmullRomClosed,
        tension: 'alpha',
        value: 0.5
      },
      'catmull-rom-open': {
        curve: d3Shape.curveCatmullRomOpen,
        tension: 'alpha',
        value: 0.5
      },
      'linear': {
        curve: d3Shape.curveLinear
      },
      'linear-closed': {
        curve: d3Shape.curveLinearClosed
      },
      'monotone': {
        horizontal: d3Shape.curveMonotoneY,
        vertical:   d3Shape.curveMonotoneX
      },
      'natural': {
        curve: d3Shape.curveNatural
      },
      'step': {
        curve: d3Shape.curveStep
      },
      'step-after': {
        curve: d3Shape.curveStepAfter
      },
      'step-before': {
        curve: d3Shape.curveStepBefore
      }
    };
  
    function curves(type, orientation, tension) {
      var entry = lookup.hasOwnProperty(type) && lookup[type],
          curve = null;
  
      if (entry) {
        curve = entry.curve || entry[orientation || 'vertical'];
        if (entry.tension && tension != null) {
          curve = curve[entry.tension](tension);
        }
      }
  
      return curve;
    }
  
    // Path parsing and rendering code adapted from fabric.js -- Thanks!
    var cmdlen = { m:2, l:2, h:1, v:1, c:6, s:4, q:4, t:2, a:7 },
        regexp = [/([MLHVCSQTAZmlhvcsqtaz])/g, /###/, /(\d)([-+])/g, /\s|,|###/];
  
    function pathParse(pathstr) {
      var result = [],
          path,
          curr,
          chunks,
          parsed, param,
          cmd, len, i, j, n, m;
  
      // First, break path into command sequence
      path = pathstr
        .slice()
        .replace(regexp[0], '###$1')
        .split(regexp[1])
        .slice(1);
  
      // Next, parse each command in turn
      for (i=0, n=path.length; i<n; ++i) {
        curr = path[i];
        chunks = curr
          .slice(1)
          .trim()
          .replace(regexp[2],'$1###$2')
          .split(regexp[3]);
        cmd = curr.charAt(0);
  
        parsed = [cmd];
        for (j=0, m=chunks.length; j<m; ++j) {
          if ((param = +chunks[j]) === param) { // not NaN
            parsed.push(param);
          }
        }
  
        len = cmdlen[cmd.toLowerCase()];
        if (parsed.length-1 > len) {
          for (j=1, m=parsed.length; j<m; j+=len) {
            result.push([cmd].concat(parsed.slice(j, j+len)));
          }
        }
        else {
          result.push(parsed);
        }
      }
  
      return result;
    }
  
    var DegToRad = Math.PI / 180;
    var HalfPi = Math.PI / 2;
    var Tau = Math.PI * 2;
    var HalfSqrt3 = Math.sqrt(3) / 2;
  
    var segmentCache = {};
    var bezierCache = {};
  
    var join = [].join;
  
    // Copied from Inkscape svgtopdf, thanks!
    function segments(x, y, rx, ry, large, sweep, rotateX, ox, oy) {
      var key = join.call(arguments);
      if (segmentCache[key]) {
        return segmentCache[key];
      }
  
      var th = rotateX * DegToRad;
      var sin_th = Math.sin(th);
      var cos_th = Math.cos(th);
      rx = Math.abs(rx);
      ry = Math.abs(ry);
      var px = cos_th * (ox - x) * 0.5 + sin_th * (oy - y) * 0.5;
      var py = cos_th * (oy - y) * 0.5 - sin_th * (ox - x) * 0.5;
      var pl = (px*px) / (rx*rx) + (py*py) / (ry*ry);
      if (pl > 1) {
        pl = Math.sqrt(pl);
        rx *= pl;
        ry *= pl;
      }
  
      var a00 = cos_th / rx;
      var a01 = sin_th / rx;
      var a10 = (-sin_th) / ry;
      var a11 = (cos_th) / ry;
      var x0 = a00 * ox + a01 * oy;
      var y0 = a10 * ox + a11 * oy;
      var x1 = a00 * x + a01 * y;
      var y1 = a10 * x + a11 * y;
  
      var d = (x1-x0) * (x1-x0) + (y1-y0) * (y1-y0);
      var sfactor_sq = 1 / d - 0.25;
      if (sfactor_sq < 0) sfactor_sq = 0;
      var sfactor = Math.sqrt(sfactor_sq);
      if (sweep == large) sfactor = -sfactor;
      var xc = 0.5 * (x0 + x1) - sfactor * (y1-y0);
      var yc = 0.5 * (y0 + y1) + sfactor * (x1-x0);
  
      var th0 = Math.atan2(y0-yc, x0-xc);
      var th1 = Math.atan2(y1-yc, x1-xc);
  
      var th_arc = th1-th0;
      if (th_arc < 0 && sweep === 1) {
        th_arc += Tau;
      } else if (th_arc > 0 && sweep === 0) {
        th_arc -= Tau;
      }
  
      var segs = Math.ceil(Math.abs(th_arc / (HalfPi + 0.001)));
      var result = [];
      for (var i=0; i<segs; ++i) {
        var th2 = th0 + i * th_arc / segs;
        var th3 = th0 + (i+1) * th_arc / segs;
        result[i] = [xc, yc, th2, th3, rx, ry, sin_th, cos_th];
      }
  
      return (segmentCache[key] = result);
    }
  
    function bezier(params) {
      var key = join.call(params);
      if (bezierCache[key]) {
        return bezierCache[key];
      }
  
      var cx = params[0],
          cy = params[1],
          th0 = params[2],
          th1 = params[3],
          rx = params[4],
          ry = params[5],
          sin_th = params[6],
          cos_th = params[7];
  
      var a00 = cos_th * rx;
      var a01 = -sin_th * ry;
      var a10 = sin_th * rx;
      var a11 = cos_th * ry;
  
      var cos_th0 = Math.cos(th0);
      var sin_th0 = Math.sin(th0);
      var cos_th1 = Math.cos(th1);
      var sin_th1 = Math.sin(th1);
  
      var th_half = 0.5 * (th1 - th0);
      var sin_th_h2 = Math.sin(th_half * 0.5);
      var t = (8/3) * sin_th_h2 * sin_th_h2 / Math.sin(th_half);
      var x1 = cx + cos_th0 - t * sin_th0;
      var y1 = cy + sin_th0 + t * cos_th0;
      var x3 = cx + cos_th1;
      var y3 = cy + sin_th1;
      var x2 = x3 + t * sin_th1;
      var y2 = y3 - t * cos_th1;
  
      return (bezierCache[key] = [
        a00 * x1 + a01 * y1,  a10 * x1 + a11 * y1,
        a00 * x2 + a01 * y2,  a10 * x2 + a11 * y2,
        a00 * x3 + a01 * y3,  a10 * x3 + a11 * y3
      ]);
    }
  
    var temp = ['l', 0, 0, 0, 0, 0, 0, 0];
  
    function scale(current, s) {
      var c = (temp[0] = current[0]);
      if (c === 'a' || c === 'A') {
        temp[1] = s * current[1];
        temp[2] = s * current[2];
        temp[3] = current[3];
        temp[4] = current[4];
        temp[5] = current[5];
        temp[6] = s * current[6];
        temp[7] = s * current[7];
      } else {
        for (var i=1, n=current.length; i<n; ++i) {
          temp[i] = s * current[i];
        }
      }
      return temp;
    }
  
    function pathRender(context, path, l, t, s) {
      var current, // current instruction
          previous = null,
          x = 0, // current x
          y = 0, // current y
          controlX = 0, // current control point x
          controlY = 0, // current control point y
          tempX,
          tempY,
          tempControlX,
          tempControlY;
  
      if (l == null) l = 0;
      if (t == null) t = 0;
      if (s == null) s = 1;
  
      if (context.beginPath) context.beginPath();
  
      for (var i=0, len=path.length; i<len; ++i) {
        current = path[i];
        if (s !== 1) current = scale(current, s);
  
        switch (current[0]) { // first letter
  
          case 'l': // lineto, relative
            x += current[1];
            y += current[2];
            context.lineTo(x + l, y + t);
            break;
  
          case 'L': // lineto, absolute
            x = current[1];
            y = current[2];
            context.lineTo(x + l, y + t);
            break;
  
          case 'h': // horizontal lineto, relative
            x += current[1];
            context.lineTo(x + l, y + t);
            break;
  
          case 'H': // horizontal lineto, absolute
            x = current[1];
            context.lineTo(x + l, y + t);
            break;
  
          case 'v': // vertical lineto, relative
            y += current[1];
            context.lineTo(x + l, y + t);
            break;
  
          case 'V': // verical lineto, absolute
            y = current[1];
            context.lineTo(x + l, y + t);
            break;
  
          case 'm': // moveTo, relative
            x += current[1];
            y += current[2];
            context.moveTo(x + l, y + t);
            break;
  
          case 'M': // moveTo, absolute
            x = current[1];
            y = current[2];
            context.moveTo(x + l, y + t);
            break;
  
          case 'c': // bezierCurveTo, relative
            tempX = x + current[5];
            tempY = y + current[6];
            controlX = x + current[3];
            controlY = y + current[4];
            context.bezierCurveTo(
              x + current[1] + l, // x1
              y + current[2] + t, // y1
              controlX + l, // x2
              controlY + t, // y2
              tempX + l,
              tempY + t
            );
            x = tempX;
            y = tempY;
            break;
  
          case 'C': // bezierCurveTo, absolute
            x = current[5];
            y = current[6];
            controlX = current[3];
            controlY = current[4];
            context.bezierCurveTo(
              current[1] + l,
              current[2] + t,
              controlX + l,
              controlY + t,
              x + l,
              y + t
            );
            break;
  
          case 's': // shorthand cubic bezierCurveTo, relative
            // transform to absolute x,y
            tempX = x + current[3];
            tempY = y + current[4];
            // calculate reflection of previous control points
            controlX = 2 * x - controlX;
            controlY = 2 * y - controlY;
            context.bezierCurveTo(
              controlX + l,
              controlY + t,
              x + current[1] + l,
              y + current[2] + t,
              tempX + l,
              tempY + t
            );
  
            // set control point to 2nd one of this command
            // the first control point is assumed to be the reflection of
            // the second control point on the previous command relative
            // to the current point.
            controlX = x + current[1];
            controlY = y + current[2];
  
            x = tempX;
            y = tempY;
            break;
  
          case 'S': // shorthand cubic bezierCurveTo, absolute
            tempX = current[3];
            tempY = current[4];
            // calculate reflection of previous control points
            controlX = 2*x - controlX;
            controlY = 2*y - controlY;
            context.bezierCurveTo(
              controlX + l,
              controlY + t,
              current[1] + l,
              current[2] + t,
              tempX + l,
              tempY + t
            );
            x = tempX;
            y = tempY;
            // set control point to 2nd one of this command
            // the first control point is assumed to be the reflection of
            // the second control point on the previous command relative
            // to the current point.
            controlX = current[1];
            controlY = current[2];
  
            break;
  
          case 'q': // quadraticCurveTo, relative
            // transform to absolute x,y
            tempX = x + current[3];
            tempY = y + current[4];
  
            controlX = x + current[1];
            controlY = y + current[2];
  
            context.quadraticCurveTo(
              controlX + l,
              controlY + t,
              tempX + l,
              tempY + t
            );
            x = tempX;
            y = tempY;
            break;
  
          case 'Q': // quadraticCurveTo, absolute
            tempX = current[3];
            tempY = current[4];
  
            context.quadraticCurveTo(
              current[1] + l,
              current[2] + t,
              tempX + l,
              tempY + t
            );
            x = tempX;
            y = tempY;
            controlX = current[1];
            controlY = current[2];
            break;
  
          case 't': // shorthand quadraticCurveTo, relative
  
            // transform to absolute x,y
            tempX = x + current[1];
            tempY = y + current[2];
  
            if (previous[0].match(/[QqTt]/) === null) {
              // If there is no previous command or if the previous command was not a Q, q, T or t,
              // assume the control point is coincident with the current point
              controlX = x;
              controlY = y;
            }
            else if (previous[0] === 't') {
              // calculate reflection of previous control points for t
              controlX = 2 * x - tempControlX;
              controlY = 2 * y - tempControlY;
            }
            else if (previous[0] === 'q') {
              // calculate reflection of previous control points for q
              controlX = 2 * x - controlX;
              controlY = 2 * y - controlY;
            }
  
            tempControlX = controlX;
            tempControlY = controlY;
  
            context.quadraticCurveTo(
              controlX + l,
              controlY + t,
              tempX + l,
              tempY + t
            );
            x = tempX;
            y = tempY;
            controlX = x + current[1];
            controlY = y + current[2];
            break;
  
          case 'T':
            tempX = current[1];
            tempY = current[2];
  
            // calculate reflection of previous control points
            controlX = 2 * x - controlX;
            controlY = 2 * y - controlY;
            context.quadraticCurveTo(
              controlX + l,
              controlY + t,
              tempX + l,
              tempY + t
            );
            x = tempX;
            y = tempY;
            break;
  
          case 'a':
            drawArc(context, x + l, y + t, [
              current[1],
              current[2],
              current[3],
              current[4],
              current[5],
              current[6] + x + l,
              current[7] + y + t
            ]);
            x += current[6];
            y += current[7];
            break;
  
          case 'A':
            drawArc(context, x + l, y + t, [
              current[1],
              current[2],
              current[3],
              current[4],
              current[5],
              current[6] + l,
              current[7] + t
            ]);
            x = current[6];
            y = current[7];
            break;
  
          case 'z':
          case 'Z':
            context.closePath();
            break;
        }
        previous = current;
      }
    }
  
    function drawArc(context, x, y, coords) {
      var seg = segments(
        coords[5], // end x
        coords[6], // end y
        coords[0], // radius x
        coords[1], // radius y
        coords[3], // large flag
        coords[4], // sweep flag
        coords[2], // rotation
        x, y
      );
      for (var i=0; i<seg.length; ++i) {
        var bez = bezier(seg[i]);
        context.bezierCurveTo(bez[0], bez[1], bez[2], bez[3], bez[4], bez[5]);
      }
    }
  
    var Tan30 = 0.5773502691896257;
  
    var builtins = {
      'circle': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2;
          context.moveTo(r, 0);
          context.arc(0, 0, r, 0, Tau);
        }
      },
      'cross': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              s = r / 2.5;
          context.moveTo(-r, -s);
          context.lineTo(-r, s);
          context.lineTo(-s, s);
          context.lineTo(-s, r);
          context.lineTo(s, r);
          context.lineTo(s, s);
          context.lineTo(r, s);
          context.lineTo(r, -s);
          context.lineTo(s, -s);
          context.lineTo(s, -r);
          context.lineTo(-s, -r);
          context.lineTo(-s, -s);
          context.closePath();
        }
      },
      'diamond': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2;
          context.moveTo(-r, 0);
          context.lineTo(0, -r);
          context.lineTo(r, 0);
          context.lineTo(0, r);
          context.closePath();
        }
      },
      'square': {
        draw: function(context, size) {
          var w = Math.sqrt(size),
              x = -w / 2;
          context.rect(x, x, w, w);
        }
      },
      'arrow': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              s = r / 7,
              t = r / 2.5,
              v = r / 8;
          context.moveTo(-s, r);
          context.lineTo(s, r);
          context.lineTo(s, -v);
          context.lineTo(t, -v);
          context.lineTo(0, -r);
          context.lineTo(-t, -v);
          context.lineTo(-s, -v);
          context.closePath();
        }
      },
      'wedge': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              h = HalfSqrt3 * r,
              o = (h - r * Tan30),
              b = r / 4;
          context.moveTo(0, -h - o);
          context.lineTo(-b, h - o);
          context.lineTo(b, h - o);
          context.closePath();
        }
      },
      'triangle': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              h = HalfSqrt3 * r,
              o = (h - r * Tan30);
          context.moveTo(0, -h - o);
          context.lineTo(-r, h - o);
          context.lineTo(r, h - o);
          context.closePath();
        }
      },
      'triangle-up': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              h = HalfSqrt3 * r;
          context.moveTo(0, -h);
          context.lineTo(-r, h);
          context.lineTo(r, h);
          context.closePath();
        }
      },
      'triangle-down': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              h = HalfSqrt3 * r;
          context.moveTo(0, h);
          context.lineTo(-r, -h);
          context.lineTo(r, -h);
          context.closePath();
        }
      },
      'triangle-right': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              h = HalfSqrt3 * r;
          context.moveTo(h, 0);
          context.lineTo(-h, -r);
          context.lineTo(-h, r);
          context.closePath();
        }
      },
      'triangle-left': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2,
              h = HalfSqrt3 * r;
          context.moveTo(-h, 0);
          context.lineTo(h, -r);
          context.lineTo(h, r);
          context.closePath();
        }
      },
      'stroke': {
        draw: function(context, size) {
          var r = Math.sqrt(size) / 2;
          context.moveTo(-r, 0);
          context.lineTo(r, 0);
        }
      }
    };
  
    function symbols(_) {
      return builtins.hasOwnProperty(_) ? builtins[_] : customSymbol(_);
    }
  
    var custom = {};
  
    function customSymbol(path) {
      if (!custom.hasOwnProperty(path)) {
        var parsed = pathParse(path);
        custom[path] = {
          draw: function(context, size) {
            pathRender(context, parsed, 0, 0, Math.sqrt(size) / 2);
          }
        };
      }
      return custom[path];
    }
  
    function rectangleX(d) {
      return d.x;
    }
  
    function rectangleY(d) {
      return d.y;
    }
  
    function rectangleWidth(d) {
      return d.width;
    }
  
    function rectangleHeight(d) {
      return d.height;
    }
  
    function constant$1(_) {
      return function() { return _; };
    }
  
    function vg_rect() {
      var x = rectangleX,
          y = rectangleY,
          width = rectangleWidth,
          height = rectangleHeight,
          cornerRadius = constant$1(0),
          context = null;
  
      function rectangle(_, x0, y0) {
        var buffer,
            x1 = x0 != null ? x0 : +x.call(this, _),
            y1 = y0 != null ? y0 : +y.call(this, _),
            w  = +width.call(this, _),
            h  = +height.call(this, _),
            cr = +cornerRadius.call(this, _);
  
        if (!context) context = buffer = d3Path.path();
  
        if (cr <= 0) {
          context.rect(x1, y1, w, h);
        } else {
          var x2 = x1 + w,
              y2 = y1 + h;
          context.moveTo(x1 + cr, y1);
          context.lineTo(x2 - cr, y1);
          context.quadraticCurveTo(x2, y1, x2, y1 + cr);
          context.lineTo(x2, y2 - cr);
          context.quadraticCurveTo(x2, y2, x2 - cr, y2);
          context.lineTo(x1 + cr, y2);
          context.quadraticCurveTo(x1, y2, x1, y2 - cr);
          context.lineTo(x1, y1 + cr);
          context.quadraticCurveTo(x1, y1, x1 + cr, y1);
          context.closePath();
        }
  
        if (buffer) {
          context = null;
          return buffer + '' || null;
        }
      }
  
      rectangle.x = function(_) {
        if (arguments.length) {
          x = typeof _ === 'function' ? _ : constant$1(+_);
          return rectangle;
        } else {
          return x;
        }
      };
  
      rectangle.y = function(_) {
        if (arguments.length) {
          y = typeof _ === 'function' ? _ : constant$1(+_);
          return rectangle;
        } else {
          return y;
        }
      };
  
      rectangle.width = function(_) {
        if (arguments.length) {
          width = typeof _ === 'function' ? _ : constant$1(+_);
          return rectangle;
        } else {
          return width;
        }
      };
  
      rectangle.height = function(_) {
        if (arguments.length) {
          height = typeof _ === 'function' ? _ : constant$1(+_);
          return rectangle;
        } else {
          return height;
        }
      };
  
      rectangle.cornerRadius = function(_) {
        if (arguments.length) {
          cornerRadius = typeof _ === 'function' ? _ : constant$1(+_);
          return rectangle;
        } else {
          return cornerRadius;
        }
      };
  
      rectangle.context = function(_) {
        if (arguments.length) {
          context = _ == null ? null : _;
          return rectangle;
        } else {
          return context;
        }
      };
  
      return rectangle;
    }
  
    function vg_trail() {
      var x,
          y,
          size,
          defined,
          context = null,
          ready, x1, y1, r1;
  
      function point(x2, y2, w2) {
        var r2 = w2 / 2;
  
        if (ready) {
          var ux = y1 - y2,
              uy = x2 - x1;
  
          if (ux || uy) {
            // get normal vector
            var ud = Math.sqrt(ux * ux + uy * uy),
                rx = (ux /= ud) * r1,
                ry = (uy /= ud) * r1,
                t = Math.atan2(uy, ux);
  
            // draw segment
            context.moveTo(x1 - rx, y1 - ry);
            context.lineTo(x2 - ux * r2, y2 - uy * r2);
            context.arc(x2, y2, r2, t - Math.PI, t);
            context.lineTo(x1 + rx, y1 + ry);
            context.arc(x1, y1, r1, t, t + Math.PI);
          } else {
            context.arc(x2, y2, r2, 0, Tau);
          }
          context.closePath();
        } else {
          ready = 1;
        }
        x1 = x2;
        y1 = y2;
        r1 = r2;
      }
  
      function trail(data) {
        var i,
            n = data.length,
            d,
            defined0 = false,
            buffer;
  
        if (context == null) context = buffer = d3Path.path();
  
        for (i = 0; i <= n; ++i) {
          if (!(i < n && defined(d = data[i], i, data)) === defined0) {
            if (defined0 = !defined0) ready = 0;
          }
          if (defined0) point(+x(d, i, data), +y(d, i, data), +size(d, i, data));
        }
  
        if (buffer) {
          context = null;
          return buffer + '' || null;
        }
      }
  
      trail.x = function(_) {
        if (arguments.length) {
          x = _;
          return trail;
        } else {
          return x;
        }
      };
  
      trail.y = function(_) {
        if (arguments.length) {
          y = _;
          return trail;
        } else {
          return y;
        }
      };
  
      trail.size = function(_) {
        if (arguments.length) {
          size = _;
          return trail;
        } else {
          return size;
        }
      };
  
      trail.defined = function(_) {
        if (arguments.length) {
          defined = _;
          return trail;
        } else {
          return defined;
        }
      };
  
      trail.context = function(_) {
        if (arguments.length) {
          if (_ == null) {
            context = null;
          } else {
            context = _;
          }
          return trail;
        } else {
          return context;
        }
      };
  
      return trail;
    }
  
    function x(item)    { return item.x || 0; }
    function y(item)    { return item.y || 0; }
    function w(item)    { return item.width || 0; }
    function ts(item)   { return item.size || 1; }
    function h(item)    { return item.height || 0; }
    function xw(item)   { return (item.x || 0) + (item.width || 0); }
    function yh(item)   { return (item.y || 0) + (item.height || 0); }
    function sa(item)   { return item.startAngle || 0; }
    function ea(item)   { return item.endAngle || 0; }
    function pa(item)   { return item.padAngle || 0; }
    function ir(item)   { return item.innerRadius || 0; }
    function or(item)   { return item.outerRadius || 0; }
    function cr(item)   { return item.cornerRadius || 0; }
    function def(item)  { return !(item.defined === false); }
    function size(item) { return item.size == null ? 64 : item.size; }
    function type(item) { return symbols(item.shape || 'circle'); }
  
    var arcShape    = d3Shape.arc().startAngle(sa).endAngle(ea).padAngle(pa)
                              .innerRadius(ir).outerRadius(or).cornerRadius(cr),
        areavShape  = d3Shape.area().x(x).y1(y).y0(yh).defined(def),
        areahShape  = d3Shape.area().y(y).x1(x).x0(xw).defined(def),
        lineShape   = d3Shape.line().x(x).y(y).defined(def),
        rectShape   = vg_rect().x(x).y(y).width(w).height(h).cornerRadius(cr),
        symbolShape = d3Shape.symbol().type(type).size(size),
        trailShape  = vg_trail().x(x).y(y).defined(def).size(ts);
  
    function arc(context, item) {
      return arcShape.context(context)(item);
    }
  
    function area(context, items) {
      var item = items[0],
          interp = item.interpolate || 'linear';
      return (item.orient === 'horizontal' ? areahShape : areavShape)
        .curve(curves(interp, item.orient, item.tension))
        .context(context)(items);
    }
  
    function line(context, items) {
      var item = items[0],
          interp = item.interpolate || 'linear';
      return lineShape.curve(curves(interp, item.orient, item.tension))
        .context(context)(items);
    }
  
    function rectangle(context, item, x, y) {
      return rectShape.context(context)(item, x, y);
    }
  
    function shape(context, item) {
      return (item.mark.shape || item.shape)
        .context(context)(item);
    }
  
    function symbol(context, item) {
      return symbolShape.context(context)(item);
    }
  
    function trail(context, items) {
      return trailShape.context(context)(items);
    }
  
    function boundStroke(bounds, item) {
      if (item.stroke && item.opacity !== 0 && item.strokeOpacity !== 0) {
        bounds.expand(item.strokeWidth != null ? +item.strokeWidth : 1);
      }
      return bounds;
    }
  
    var bounds,
        circleThreshold = Tau - 1e-8;
  
    function context(_) {
      bounds = _;
      return context;
    }
  
    function noop() {}
  
    function add$1(x, y) { bounds.add(x, y); }
  
    context.beginPath = noop;
  
    context.closePath = noop;
  
    context.moveTo = add$1;
  
    context.lineTo = add$1;
  
    context.rect = function(x, y, w, h) {
      add$1(x, y);
      add$1(x + w, y + h);
    };
  
    context.quadraticCurveTo = function(x1, y1, x2, y2) {
      add$1(x1, y1);
      add$1(x2, y2);
    };
  
    context.bezierCurveTo = function(x1, y1, x2, y2, x3, y3) {
      add$1(x1, y1);
      add$1(x2, y2);
      add$1(x3, y3);
    };
  
    context.arc = function(cx, cy, r, sa, ea, ccw) {
      if (Math.abs(ea - sa) > circleThreshold) {
        add$1(cx - r, cy - r);
        add$1(cx + r, cy + r);
        return;
      }
  
      var xmin = Infinity, xmax = -Infinity,
          ymin = Infinity, ymax = -Infinity,
          s, i, x, y;
  
      function update(a) {
        x = r * Math.cos(a);
        y = r * Math.sin(a);
        if (x < xmin) xmin = x;
        if (x > xmax) xmax = x;
        if (y < ymin) ymin = y;
        if (y > ymax) ymax = y;
      }
  
      // Sample end points and interior points aligned with 90 degrees
      update(sa);
      update(ea);
  
      if (ea !== sa) {
        sa = sa % Tau; if (sa < 0) sa += Tau;
        ea = ea % Tau; if (ea < 0) ea += Tau;
  
        if (ea < sa) {
          ccw = !ccw; // flip direction
          s = sa; sa = ea; ea = s; // swap end-points
        }
  
        if (ccw) {
          ea -= Tau;
          s = sa - (sa % HalfPi);
          for (i=0; i<4 && s>ea; ++i, s-=HalfPi) update(s);
        } else {
          s = sa - (sa % HalfPi) + HalfPi;
          for (i=0; i<4 && s<ea; ++i, s=s+HalfPi) update(s);
        }
      }
  
      add$1(cx + xmin, cy + ymin);
      add$1(cx + xmax, cy + ymax);
    };
  
    var context$1 = (context$1 = domCanvas(1,1))
      ? context$1.getContext('2d')
      : null;
  
    const b = new Bounds();
  
    function intersectPath(draw) {
      return function(item, brush) {
        // rely on (inaccurate) bounds intersection if no context
        if (!context$1) return true;
  
        // add path to offscreen graphics context
        draw(context$1, item);
  
        // get bounds intersection region
        b.clear().union(item.bounds).intersect(brush).round();
        const {x1, y1, x2, y2} = b;
  
        // iterate over intersection region
        // perform fine grained inclusion test
        for (let y = y1; y <= y2; ++y) {
          for (let x = x1; x <= x2; ++x) {
            if (context$1.isPointInPath(x, y)) {
              return true;
            }
          }
        }
  
        // false if no hits in intersection region
        return false;
      }
    }
  
    function intersectPoint(item, box) {
      return box.contains(item.x || 0, item.y || 0);
    }
  
    function intersectRect(item, box) {
      const x = item.x || 0,
            y = item.y || 0,
            w = item.width || 0,
            h = item.height || 0;
      return box.intersects(b.set(x, y, x + w, y + h));
    }
  
    function intersectRule(item, box) {
      const x = item.x || 0,
            y = item.y || 0,
            x2 = item.x2 != null ? item.x2 : x,
            y2 = item.y2 != null ? item.y2 : y;
      return intersectBoxLine(box, x, y, x2, y2);
    }
  
    function intersectBoxLine(box, x, y, u, v) {
      const {x1, y1, x2, y2} = box,
            dx = u - x,
            dy = v - y;
  
      let t0 = 0, t1 = 1, p, q, r, e;
  
      for (e=0; e<4; ++e) {
        if (e === 0) { p = -dx; q = -(x1 - x); }
        if (e === 1) { p =  dx; q =  (x2 - x); }
        if (e === 2) { p = -dy; q = -(y1 - y); }
        if (e === 3) { p =  dy; q =  (y2 - y); }
  
        if (Math.abs(p) < 1e-10 && q < 0) return false;
  
        r = q / p;
  
        if (p < 0) {
          if (r > t1) return false;
          else if (r > t0) t0 = r;
        } else if (p > 0) {
          if (r < t0) return false;
          else if (r < t1) t1 = r;
        }
      }
  
      return true;
    }
  
    function gradient(context, gradient, bounds) {
      const w = bounds.width(),
            h = bounds.height(),
            stop = gradient.stops,
            n = stop.length;
  
      const canvasGradient = gradient.gradient === 'radial'
        ? context.createRadialGradient(
            bounds.x1 + (gradient.x1 || 0.5) * w,
            bounds.y1 + (gradient.y1 || 0.5) * h,
            Math.max(w, h) * (gradient.r1 || 0),
            bounds.x1 + (gradient.x2 || 0.5) * w,
            bounds.y1 + (gradient.y2 || 0.5) * h,
            Math.max(w, h) * (gradient.r2 || 0.5)
          )
        : context.createLinearGradient(
            bounds.x1 + (gradient.x1 || 0) * w,
            bounds.y1 + (gradient.y1 || 0) * h,
            bounds.x1 + (gradient.x2 || 1) * w,
            bounds.y1 + (gradient.y2 || 0) * h
          );
  
      for (let i=0; i<n; ++i) {
        canvasGradient.addColorStop(stop[i].offset, stop[i].color);
      }
  
      return canvasGradient;
    }
  
    function color(context, item, value) {
      return isGradient(value) ?
        gradient(context, value, item.bounds) :
        value;
    }
  
    function fill(context, item, opacity) {
      opacity *= (item.fillOpacity==null ? 1 : item.fillOpacity);
      if (opacity > 0) {
        context.globalAlpha = opacity;
        context.fillStyle = color(context, item, item.fill);
        return true;
      } else {
        return false;
      }
    }
  
    var Empty$1 = [];
  
    function stroke(context, item, opacity) {
      var lw = (lw = item.strokeWidth) != null ? lw : 1;
  
      if (lw <= 0) return false;
  
      opacity *= (item.strokeOpacity==null ? 1 : item.strokeOpacity);
      if (opacity > 0) {
        context.globalAlpha = opacity;
        context.strokeStyle = color(context, item, item.stroke);
  
        context.lineWidth = lw;
        context.lineCap = item.strokeCap || 'butt';
        context.lineJoin = item.strokeJoin || 'miter';
        context.miterLimit = item.strokeMiterLimit || 10;
  
        if (context.setLineDash) {
          context.setLineDash(item.strokeDash || Empty$1);
          context.lineDashOffset = item.strokeDashOffset || 0;
        }
        return true;
      } else {
        return false;
      }
    }
  
    function compare$1(a, b) {
      return a.zindex - b.zindex || a.index - b.index;
    }
  
    function zorder(scene) {
      if (!scene.zdirty) return scene.zitems;
  
      var items = scene.items,
          output = [], item, i, n;
  
      for (i=0, n=items.length; i<n; ++i) {
        item = items[i];
        item.index = i;
        if (item.zindex) output.push(item);
      }
  
      scene.zdirty = false;
      return scene.zitems = output.sort(compare$1);
    }
  
    function visit(scene, visitor) {
      var items = scene.items, i, n;
      if (!items || !items.length) return;
  
      var zitems = zorder(scene);
  
      if (zitems && zitems.length) {
        for (i=0, n=items.length; i<n; ++i) {
          if (!items[i].zindex) visitor(items[i]);
        }
        items = zitems;
      }
  
      for (i=0, n=items.length; i<n; ++i) {
        visitor(items[i]);
      }
    }
  
    function pickVisit(scene, visitor) {
      var items = scene.items, hit, i;
      if (!items || !items.length) return null;
  
      var zitems = zorder(scene);
      if (zitems && zitems.length) items = zitems;
  
      for (i=items.length; --i >= 0;) {
        if (hit = visitor(items[i])) return hit;
      }
  
      if (items === zitems) {
        for (items=scene.items, i=items.length; --i >= 0;) {
          if (!items[i].zindex) {
            if (hit = visitor(items[i])) return hit;
          }
        }
      }
  
      return null;
    }
  
    function drawAll(path) {
      return function(context, scene, bounds) {
        visit(scene, function(item) {
          if (!bounds || bounds.intersects(item.bounds)) {
            drawPath(path, context, item, item);
          }
        });
      };
    }
  
    function drawOne(path) {
      return function(context, scene, bounds) {
        if (scene.items.length && (!bounds || bounds.intersects(scene.bounds))) {
          drawPath(path, context, scene.items[0], scene.items);
        }
      };
    }
  
    function drawPath(path, context, item, items) {
      var opacity = item.opacity == null ? 1 : item.opacity;
      if (opacity === 0) return;
  
      if (path(context, items)) return;
  
      if (item.fill && fill(context, item, opacity)) {
        context.fill();
      }
  
      if (item.stroke && stroke(context, item, opacity)) {
        context.stroke();
      }
    }
  
    function pick(test) {
      test = test || truthy;
  
      return function(context, scene, x, y, gx, gy) {
        x *= context.pixelRatio;
        y *= context.pixelRatio;
  
        return pickVisit(scene, function(item) {
          var b = item.bounds;
          // first hit test against bounding box
          if ((b && !b.contains(gx, gy)) || !b) return;
          // if in bounding box, perform more careful test
          if (test(context, item, x, y, gx, gy)) return item;
        });
      };
    }
  
    function hitPath(path, filled) {
      return function(context, o, x, y) {
        var item = Array.isArray(o) ? o[0] : o,
            fill = (filled == null) ? item.fill : filled,
            stroke = item.stroke && context.isPointInStroke, lw, lc;
  
        if (stroke) {
          lw = item.strokeWidth;
          lc = item.strokeCap;
          context.lineWidth = lw != null ? lw : 1;
          context.lineCap   = lc != null ? lc : 'butt';
        }
  
        return path(context, o) ? false :
          (fill && context.isPointInPath(x, y)) ||
          (stroke && context.isPointInStroke(x, y));
      };
    }
  
    function pickPath(path) {
      return pick(hitPath(path));
    }
  
    function translate(x, y) {
      return 'translate(' + x + ',' + y + ')';
    }
  
    function rotate(a) {
      return 'rotate(' + a + ')';
    }
  
    function translateItem(item) {
      return translate(item.x || 0, item.y || 0);
    }
  
    function transformItem(item) {
      return translate(item.x || 0, item.y || 0)
        + (item.angle ? ' ' + rotate(item.angle) : '');
    }
  
    function markItemPath(type, shape, isect) {
  
      function attr(emit, item) {
        emit('transform', transformItem(item));
        emit('d', shape(null, item));
      }
  
      function bound(bounds, item) {
        var x = item.x || 0,
            y = item.y || 0;
  
        shape(context(bounds), item);
        boundStroke(bounds, item).translate(x, y);
        if (item.angle) {
          bounds.rotate(item.angle * DegToRad, x, y);
        }
  
        return bounds;
      }
  
      function draw(context, item) {
        var x = item.x || 0,
            y = item.y || 0,
            a = item.angle || 0;
  
        context.translate(x, y);
        if (a) context.rotate(a *= DegToRad);
        context.beginPath();
        shape(context, item);
        if (a) context.rotate(-a);
        context.translate(-x, -y);
      }
  
      return {
        type:   type,
        tag:    'path',
        nested: false,
        attr:   attr,
        bound:  bound,
        draw:   drawAll(draw),
        pick:   pickPath(draw),
        isect:  isect || intersectPath(draw)
      };
  
    }
  
    var arc$1 = markItemPath('arc', arc);
  
    function pickArea(a, p) {
      var v = a[0].orient === 'horizontal' ? p[1] : p[0],
          z = a[0].orient === 'horizontal' ? 'y' : 'x',
          i = a.length,
          min = +Infinity, hit, d;
  
      while (--i >= 0) {
        if (a[i].defined === false) continue;
        d = Math.abs(a[i][z] - v);
        if (d < min) {
          min = d;
          hit = a[i];
        }
      }
  
      return hit;
    }
  
    function pickLine(a, p) {
      var t = Math.pow(a[0].strokeWidth || 1, 2),
          i = a.length, dx, dy, dd;
  
      while (--i >= 0) {
        if (a[i].defined === false) continue;
        dx = a[i].x - p[0];
        dy = a[i].y - p[1];
        dd = dx * dx + dy * dy;
        if (dd < t) return a[i];
      }
  
      return null;
    }
  
    function pickTrail(a, p) {
      var i = a.length, dx, dy, dd;
  
      while (--i >= 0) {
        if (a[i].defined === false) continue;
        dx = a[i].x - p[0];
        dy = a[i].y - p[1];
        dd = dx * dx + dy * dy;
        dx = a[i].size || 1;
        if (dd < dx*dx) return a[i];
      }
  
      return null;
    }
  
    function markMultiItemPath(type, shape, tip) {
  
      function attr(emit, item) {
        var items = item.mark.items;
        if (items.length) emit('d', shape(null, items));
      }
  
      function bound(bounds, mark) {
        var items = mark.items;
        if (items.length === 0) {
          return bounds;
        } else {
          shape(context(bounds), items);
          return boundStroke(bounds, items[0]);
        }
      }
  
      function draw(context, items) {
        context.beginPath();
        shape(context, items);
      }
  
      var hit = hitPath(draw);
  
      function pick(context, scene, x, y, gx, gy) {
        var items = scene.items,
            b = scene.bounds;
  
        if (!items || !items.length || b && !b.contains(gx, gy)) {
          return null;
        }
  
        x *= context.pixelRatio;
        y *= context.pixelRatio;
        return hit(context, items, x, y) ? items[0] : null;
      }
  
      return {
        type:   type,
        tag:    'path',
        nested: true,
        attr:   attr,
        bound:  bound,
        draw:   drawOne(draw),
        pick:   pick,
        isect:  intersectPoint,
        tip:    tip
      };
  
    }
  
    var area$1 = markMultiItemPath('area', area, pickArea);
  
    var clip_id = 1;
  
    function resetSVGClipId() {
      clip_id = 1;
    }
  
    function clip(renderer, item, size) {
      var clip = item.clip,
          defs = renderer._defs,
          id = item.clip_id || (item.clip_id = 'clip' + clip_id++),
          c = defs.clipping[id] || (defs.clipping[id] = {id: id});
  
      if (isFunction(clip)) {
        c.path = clip(null);
      } else {
        c.width = size.width || 0;
        c.height = size.height || 0;
      }
  
      return 'url(#' + id + ')';
    }
  
    var StrokeOffset = 0.5;
  
    function attr(emit, item) {
      emit('transform', translateItem(item));
    }
  
    function background(emit, item) {
      var offset = item.stroke ? StrokeOffset : 0;
      emit('class', 'background');
      emit('d', rectangle(null, item, offset, offset));
    }
  
    function foreground(emit, item, renderer) {
      var url = item.clip ? clip(renderer, item, item) : null;
      emit('clip-path', url);
    }
  
    function bound(bounds, group) {
      if (!group.clip && group.items) {
        var items = group.items;
        for (var j=0, m=items.length; j<m; ++j) {
          bounds.union(items[j].bounds);
        }
      }
  
      if ((group.clip || group.width || group.height) && !group.noBound) {
        bounds.add(0, 0).add(group.width || 0, group.height || 0);
      }
  
      boundStroke(bounds, group);
  
      return bounds.translate(group.x || 0, group.y || 0);
    }
  
    function backgroundPath(context, group) {
      var offset = group.stroke ? StrokeOffset : 0;
      context.beginPath();
      rectangle(context, group, offset, offset);
    }
  
    var hitBackground = hitPath(backgroundPath);
  
    function draw(context, scene, bounds) {
      var renderer = this;
  
      visit(scene, function(group) {
        var gx = group.x || 0,
            gy = group.y || 0,
            w = group.width || 0,
            h = group.height || 0,
            opacity;
  
        // setup graphics context
        context.save();
        context.translate(gx, gy);
  
        // draw group background
        if (group.stroke || group.fill) {
          opacity = group.opacity == null ? 1 : group.opacity;
          if (opacity > 0) {
            backgroundPath(context, group);
            if (group.fill && fill(context, group, opacity)) {
              context.fill();
            }
            if (group.stroke && stroke(context, group, opacity)) {
              context.stroke();
            }
          }
        }
  
        // set clip and bounds
        if (group.clip) {
          context.beginPath();
          context.rect(0, 0, w, h);
          context.clip();
        }
        if (bounds) bounds.translate(-gx, -gy);
  
        // draw group contents
        visit(group, function(item) {
          renderer.draw(context, item, bounds);
        });
  
        // restore graphics context
        if (bounds) bounds.translate(gx, gy);
        context.restore();
      });
    }
  
    function pick$1(context, scene, x, y, gx, gy) {
      if (scene.bounds && !scene.bounds.contains(gx, gy) || !scene.items) {
        return null;
      }
  
      var handler = this,
          cx = x * context.pixelRatio,
          cy = y * context.pixelRatio;
  
      return pickVisit(scene, function(group) {
        var hit, dx, dy, b;
  
        // first hit test against bounding box
        // if a group is clipped, that should be handled by the bounds check.
        b = group.bounds;
        if (b && !b.contains(gx, gy)) return;
  
        // passed bounds check, so test sub-groups
        dx = (group.x || 0);
        dy = (group.y || 0);
  
        context.save();
        context.translate(dx, dy);
  
        dx = gx - dx;
        dy = gy - dy;
  
        // hit test against contained marks
        hit = pickVisit(group, function(mark) {
          return pickMark(mark, dx, dy)
            ? handler.pick(mark, x, y, dx, dy)
            : null;
        });
  
        // hit test against group background
        if (!hit && scene.interactive !== false
            && (group.fill || group.stroke)
            && hitBackground(context, group, cx, cy)) {
          hit = group;
        }
  
        context.restore();
        return hit || null;
      });
    }
  
    function pickMark(mark, x, y) {
      return (mark.interactive !== false || mark.marktype === 'group')
        && mark.bounds && mark.bounds.contains(x, y);
    }
  
    var group = {
      type:       'group',
      tag:        'g',
      nested:     false,
      attr:       attr,
      bound:      bound,
      draw:       draw,
      pick:       pick$1,
      isect:      intersectRect,
      background: background,
      foreground: foreground
    };
  
    function getImage(item, renderer) {
      var image = item.image;
      if (!image || image.url !== item.url) {
        image = {loaded: false, width: 0, height: 0};
        renderer.loadImage(item.url).then(function(image) {
          item.image = image;
          item.image.url = item.url;
        });
      }
      return image;
    }
  
    function imageXOffset(align, w) {
      return align === 'center' ? w / 2 : align === 'right' ? w : 0;
    }
  
    function imageYOffset(baseline, h) {
      return baseline === 'middle' ? h / 2 : baseline === 'bottom' ? h : 0;
    }
  
    function attr$1(emit, item, renderer) {
      var image = getImage(item, renderer),
          x = item.x || 0,
          y = item.y || 0,
          w = (item.width != null ? item.width : image.width) || 0,
          h = (item.height != null ? item.height : image.height) || 0,
          a = item.aspect === false ? 'none' : 'xMidYMid';
  
      x -= imageXOffset(item.align, w);
      y -= imageYOffset(item.baseline, h);
  
      emit('href', image.src || '', 'http://www.w3.org/1999/xlink', 'xlink:href');
      emit('transform', translate(x, y));
      emit('width', w);
      emit('height', h);
      emit('preserveAspectRatio', a);
    }
  
    function bound$1(bounds, item) {
      var image = item.image,
          x = item.x || 0,
          y = item.y || 0,
          w = (item.width != null ? item.width : (image && image.width)) || 0,
          h = (item.height != null ? item.height : (image && image.height)) || 0;
  
      x -= imageXOffset(item.align, w);
      y -= imageYOffset(item.baseline, h);
  
      return bounds.set(x, y, x + w, y + h);
    }
  
    function draw$1(context, scene, bounds) {
      var renderer = this;
  
      visit(scene, function(item) {
        if (bounds && !bounds.intersects(item.bounds)) return; // bounds check
  
        var image = getImage(item, renderer),
            x = item.x || 0,
            y = item.y || 0,
            w = (item.width != null ? item.width : image.width) || 0,
            h = (item.height != null ? item.height : image.height) || 0,
            opacity, ar0, ar1, t;
  
        x -= imageXOffset(item.align, w);
        y -= imageYOffset(item.baseline, h);
  
        if (item.aspect !== false) {
          ar0 = image.width / image.height;
          ar1 = item.width / item.height;
          if (ar0 === ar0 && ar1 === ar1 && ar0 !== ar1) {
            if (ar1 < ar0) {
              t = w / ar0;
              y += (h - t) / 2;
              h = t;
            } else {
              t = h * ar0;
              x += (w - t) / 2;
              w = t;
            }
          }
        }
  
        if (image.loaded) {
          context.globalAlpha = (opacity = item.opacity) != null ? opacity : 1;
          context.drawImage(image, x, y, w, h);
        }
      });
    }
  
    var image = {
      type:     'image',
      tag:      'image',
      nested:   false,
      attr:     attr$1,
      bound:    bound$1,
      draw:     draw$1,
      pick:     pick(),
      isect:    truthy, // bounds check is sufficient
      get:      getImage,
      xOffset:  imageXOffset,
      yOffset:  imageYOffset
    };
  
    var line$1 = markMultiItemPath('line', line, pickLine);
  
    function attr$2(emit, item) {
      emit('transform', translateItem(item));
      emit('d', item.path);
    }
  
    function path(context, item) {
      var path = item.path;
      if (path == null) return true;
  
      var cache = item.pathCache;
      if (!cache || cache.path !== path) {
        (item.pathCache = cache = pathParse(path)).path = path;
      }
      pathRender(context, cache, item.x, item.y);
    }
  
    function bound$2(bounds, item) {
      return path(context(bounds), item)
        ? bounds.set(0, 0, 0, 0)
        : boundStroke(bounds, item);
    }
  
    var path$1 = {
      type:   'path',
      tag:    'path',
      nested: false,
      attr:   attr$2,
      bound:  bound$2,
      draw:   drawAll(path),
      pick:   pickPath(path),
      isect:  intersectPath(path)
    };
  
    function attr$3(emit, item) {
      emit('d', rectangle(null, item));
    }
  
    function bound$3(bounds, item) {
      var x, y;
      return boundStroke(bounds.set(
        x = item.x || 0,
        y = item.y || 0,
        (x + item.width) || 0,
        (y + item.height) || 0
      ), item);
    }
  
    function draw$2(context, item) {
      context.beginPath();
      rectangle(context, item);
    }
  
    var rect = {
      type:   'rect',
      tag:    'path',
      nested: false,
      attr:   attr$3,
      bound:  bound$3,
      draw:   drawAll(draw$2),
      pick:   pickPath(draw$2),
      isect:  intersectRect
    };
  
    function attr$4(emit, item) {
      emit('transform', translateItem(item));
      emit('x2', item.x2 != null ? item.x2 - (item.x || 0) : 0);
      emit('y2', item.y2 != null ? item.y2 - (item.y || 0) : 0);
    }
  
    function bound$4(bounds, item) {
      var x1, y1;
      return boundStroke(bounds.set(
        x1 = item.x || 0,
        y1 = item.y || 0,
        item.x2 != null ? item.x2 : x1,
        item.y2 != null ? item.y2 : y1
      ), item);
    }
  
    function path$2(context, item, opacity) {
      var x1, y1, x2, y2;
  
      if (item.stroke && stroke(context, item, opacity)) {
        x1 = item.x || 0;
        y1 = item.y || 0;
        x2 = item.x2 != null ? item.x2 : x1;
        y2 = item.y2 != null ? item.y2 : y1;
        context.beginPath();
        context.moveTo(x1, y1);
        context.lineTo(x2, y2);
        return true;
      }
      return false;
    }
  
    function draw$3(context, scene, bounds) {
      visit(scene, function(item) {
        if (bounds && !bounds.intersects(item.bounds)) return; // bounds check
        var opacity = item.opacity == null ? 1 : item.opacity;
        if (opacity && path$2(context, item, opacity)) {
          context.stroke();
        }
      });
    }
  
    function hit(context, item, x, y) {
      if (!context.isPointInStroke) return false;
      return path$2(context, item, 1) && context.isPointInStroke(x, y);
    }
  
    var rule = {
      type:   'rule',
      tag:    'line',
      nested: false,
      attr:   attr$4,
      bound:  bound$4,
      draw:   draw$3,
      pick:   pick(hit),
      isect:  intersectRule
    };
  
    var shape$1 = markItemPath('shape', shape);
  
    var symbol$1 = markItemPath('symbol', symbol, intersectPoint);
  
    var currFontHeight;
  
    var textMetrics = {
      height: fontSize,
      measureWidth: measureWidth,
      estimateWidth: estimateWidth,
      width: estimateWidth,
      canvas: useCanvas
    };
  
    useCanvas(true);
  
    // make dumb, simple estimate if no canvas is available
    function estimateWidth(item) {
      currFontHeight = fontSize(item);
      return estimate(textValue(item));
    }
  
    function estimate(text) {
      return ~~(0.8 * text.length * currFontHeight);
    }
  
    // measure text width if canvas is available
    function measureWidth(item) {
      return fontSize(item) <= 0 ? 0
        : (context$1.font = font(item), measure$1(textValue(item)));
    }
  
    function measure$1(text) {
      return context$1.measureText(text).width;
    }
  
    function fontSize(item) {
      return item.fontSize != null ? item.fontSize : 11;
    }
  
    function useCanvas(use) {
      textMetrics.width = (use && context$1) ? measureWidth : estimateWidth;
    }
  
    function textValue(item) {
      var s = item.text;
      if (s == null) {
        return '';
      } else {
        return item.limit > 0 ? truncate$1(item) : s + '';
      }
    }
  
    function truncate$1(item) {
      var limit = +item.limit,
          text = item.text + '',
          width;
  
      if (textMetrics.width === measureWidth) {
        // we are using canvas
        context$1.font = font(item);
        width = measure$1;
      } else {
        // we are relying on estimates
        currFontHeight = fontSize(item);
        width = estimate;
      }
  
      if (width(text) < limit) return text;
  
      var ellipsis = item.ellipsis || '\u2026',
          rtl = item.dir === 'rtl',
          lo = 0,
          hi = text.length, mid;
  
      limit -= width(ellipsis);
  
      if (rtl) {
        while (lo < hi) {
          mid = (lo + hi >>> 1);
          if (width(text.slice(mid)) > limit) lo = mid + 1;
          else hi = mid;
        }
        return ellipsis + text.slice(lo);
      } else {
        while (lo < hi) {
          mid = 1 + (lo + hi >>> 1);
          if (width(text.slice(0, mid)) < limit) lo = mid;
          else hi = mid - 1;
        }
        return text.slice(0, lo) + ellipsis;
      }
    }
  
    function fontFamily(item, quote) {
      var font = item.font;
      return (quote && font
        ? String(font).replace(/"/g, '\'')
        : font) || 'sans-serif';
    }
  
    function font(item, quote) {
      return '' +
        (item.fontStyle ? item.fontStyle + ' ' : '') +
        (item.fontVariant ? item.fontVariant + ' ' : '') +
        (item.fontWeight ? item.fontWeight + ' ' : '') +
        fontSize(item) + 'px ' +
        fontFamily(item, quote);
    }
  
    function offset(item) {
      // perform our own font baseline calculation
      // why? not all browsers support SVG 1.1 'alignment-baseline' :(
      var baseline = item.baseline,
          h = fontSize(item);
      return Math.round(
        baseline === 'top'    ?  0.79*h :
        baseline === 'middle' ?  0.30*h :
        baseline === 'bottom' ? -0.21*h : 0
      );
    }
  
    var textAlign = {
      'left':   'start',
      'center': 'middle',
      'right':  'end'
    };
  
    var tempBounds = new Bounds();
  
    function anchorPoint(item) {
      var x = item.x || 0,
          y = item.y || 0,
          r = item.radius || 0, t;
  
      if (r) {
        t = (item.theta || 0) - HalfPi;
        x += r * Math.cos(t);
        y += r * Math.sin(t);
      }
  
      tempBounds.x1 = x;
      tempBounds.y1 = y;
      return tempBounds;
    }
  
    function attr$5(emit, item) {
      var dx = item.dx || 0,
          dy = (item.dy || 0) + offset(item),
          p = anchorPoint(item),
          x = p.x1,
          y = p.y1,
          a = item.angle || 0, t;
  
      emit('text-anchor', textAlign[item.align] || 'start');
  
      if (a) {
        t = translate(x, y) + ' ' + rotate(a);
        if (dx || dy) t += ' ' + translate(dx, dy);
      } else {
        t = translate(x + dx, y + dy);
      }
      emit('transform', t);
    }
  
    function bound$5(bounds, item, mode) {
      var h = textMetrics.height(item),
          a = item.align,
          p = anchorPoint(item),
          x = p.x1,
          y = p.y1,
          dx = item.dx || 0,
          dy = (item.dy || 0) + offset(item) - Math.round(0.8*h), // use 4/5 offset
          w;
  
      // horizontal alignment
      w = textMetrics.width(item);
      if (a === 'center') {
        dx -= (w / 2);
      } else if (a === 'right') {
        dx -= w;
      }
  
      bounds.set(dx+=x, dy+=y, dx+w, dy+h);
      if (item.angle && !mode) {
        bounds.rotate(item.angle * DegToRad, x, y);
      } else if (mode === 2) {
        return bounds.rotatedPoints(item.angle * DegToRad, x, y);
      }
      return bounds;
    }
  
    function draw$4(context, scene, bounds) {
      visit(scene, function(item) {
        var opacity, p, x, y, str;
        if (bounds && !bounds.intersects(item.bounds)) return; // bounds check
        if (!(str = textValue(item))) return; // get text string
  
        opacity = item.opacity == null ? 1 : item.opacity;
        if (opacity === 0 || item.fontSize <= 0) return;
  
        context.font = font(item);
        context.textAlign = item.align || 'left';
  
        p = anchorPoint(item);
        x = p.x1,
        y = p.y1;
  
        if (item.angle) {
          context.save();
          context.translate(x, y);
          context.rotate(item.angle * DegToRad);
          x = y = 0; // reset x, y
        }
        x += (item.dx || 0);
        y += (item.dy || 0) + offset(item);
  
        if (item.fill && fill(context, item, opacity)) {
          context.fillText(str, x, y);
        }
        if (item.stroke && stroke(context, item, opacity)) {
          context.strokeText(str, x, y);
        }
        if (item.angle) context.restore();
      });
    }
  
    function hit$1(context, item, x, y, gx, gy) {
      if (item.fontSize <= 0) return false;
      if (!item.angle) return true; // bounds sufficient if no rotation
  
      // project point into space of unrotated bounds
      var p = anchorPoint(item),
          ax = p.x1,
          ay = p.y1,
          b = bound$5(tempBounds, item, 1),
          a = -item.angle * DegToRad,
          cos = Math.cos(a),
          sin = Math.sin(a),
          px = cos * gx - sin * gy + (ax - cos * ax + sin * ay),
          py = sin * gx + cos * gy + (ay - sin * ax - cos * ay);
  
      return b.contains(px, py);
    }
  
    function intersectText(item, box) {
      var p = bound$5(tempBounds, item, 2);
      return intersectBoxLine(box, p[0], p[1], p[2], p[3])
          || intersectBoxLine(box, p[0], p[1], p[4], p[5])
          || intersectBoxLine(box, p[4], p[5], p[6], p[7])
          || intersectBoxLine(box, p[2], p[3], p[6], p[7]);
    }
  
    var text = {
      type:   'text',
      tag:    'text',
      nested: false,
      attr:   attr$5,
      bound:  bound$5,
      draw:   draw$4,
      pick:   pick(hit$1),
      isect:  intersectText
    };
  
    var trail$1 = markMultiItemPath('trail', trail, pickTrail);
  
    var Marks = {
      arc:     arc$1,
      area:    area$1,
      group:   group,
      image:   image,
      line:    line$1,
      path:    path$1,
      rect:    rect,
      rule:    rule,
      shape:   shape$1,
      symbol:  symbol$1,
      text:    text,
      trail:   trail$1
    };
  
    function boundItem(item, func, opt) {
      var type = Marks[item.mark.marktype],
          bound = func || type.bound;
      if (type.nested) item = item.mark;
  
      return bound(item.bounds || (item.bounds = new Bounds()), item, opt);
    }
  
    var DUMMY = {mark: null};
  
    function boundMark(mark, bounds, opt) {
      var type  = Marks[mark.marktype],
          bound = type.bound,
          items = mark.items,
          hasItems = items && items.length,
          i, n, item, b;
  
      if (type.nested) {
        if (hasItems) {
          item = items[0];
        } else {
          // no items, fake it
          DUMMY.mark = mark;
          item = DUMMY;
        }
        b = boundItem(item, bound, opt);
        bounds = bounds && bounds.union(b) || b;
        return bounds;
      }
  
      bounds = bounds
        || mark.bounds && mark.bounds.clear()
        || new Bounds();
  
      if (hasItems) {
        for (i=0, n=items.length; i<n; ++i) {
          bounds.union(boundItem(items[i], bound, opt));
        }
      }
  
      return mark.bounds = bounds;
    }
  
    var keys = [
      'marktype', 'name', 'role', 'interactive', 'clip', 'items', 'zindex',
      'x', 'y', 'width', 'height', 'align', 'baseline',             // layout
      'fill', 'fillOpacity', 'opacity',                             // fill
      'stroke', 'strokeOpacity', 'strokeWidth', 'strokeCap',        // stroke
      'strokeDash', 'strokeDashOffset',                             // stroke dash
      'startAngle', 'endAngle', 'innerRadius', 'outerRadius',       // arc
      'cornerRadius', 'padAngle',                                   // arc, rect
      'interpolate', 'tension', 'orient', 'defined',                // area, line
      'url',                                                        // image
      'path',                                                       // path
      'x2', 'y2',                                                   // rule
      'size', 'shape',                                              // symbol
      'text', 'angle', 'theta', 'radius', 'dx', 'dy',               // text
      'font', 'fontSize', 'fontWeight', 'fontStyle', 'fontVariant'  // font
    ];
  
    function sceneToJSON(scene, indent) {
      return JSON.stringify(scene, keys, indent);
    }
  
    function sceneFromJSON(json) {
      var scene = (typeof json === 'string' ? JSON.parse(json) : json);
      return initialize(scene);
    }
  
    function initialize(scene) {
      var type = scene.marktype,
          items = scene.items,
          parent, i, n;
  
      if (items) {
        for (i=0, n=items.length; i<n; ++i) {
          parent = type ? 'mark' : 'group';
          items[i][parent] = scene;
          if (items[i].zindex) items[i][parent].zdirty = true;
          if ('group' === (type || parent)) initialize(items[i]);
        }
      }
  
      if (type) boundMark(scene);
      return scene;
    }
  
    function Scenegraph(scene) {
      if (arguments.length) {
        this.root = sceneFromJSON(scene);
      } else {
        this.root = createMark({
          marktype: 'group',
          name: 'root',
          role: 'frame'
        });
        this.root.items = [new GroupItem(this.root)];
      }
    }
  
    var prototype$F = Scenegraph.prototype;
  
    prototype$F.toJSON = function(indent) {
      return sceneToJSON(this.root, indent || 0);
    };
  
    prototype$F.mark = function(markdef, group, index) {
      group = group || this.root.items[0];
      var mark = createMark(markdef, group);
      group.items[index] = mark;
      if (mark.zindex) mark.group.zdirty = true;
      return mark;
    };
  
    function createMark(def, group) {
      return {
        bounds:      new Bounds(),
        clip:        !!def.clip,
        group:       group,
        interactive: def.interactive === false ? false : true,
        items:       [],
        marktype:    def.marktype,
        name:        def.name || undefined,
        role:        def.role || undefined,
        zindex:      def.zindex || 0
      };
    }
  
    // create a new DOM element
    function domCreate(doc, tag, ns) {
      if (!doc && typeof document !== 'undefined' && document.createElement) {
        doc = document;
      }
      return doc
        ? (ns ? doc.createElementNS(ns, tag) : doc.createElement(tag))
        : null;
    }
  
    // find first child element with matching tag
    function domFind(el, tag) {
      tag = tag.toLowerCase();
      var nodes = el.childNodes, i = 0, n = nodes.length;
      for (; i<n; ++i) if (nodes[i].tagName.toLowerCase() === tag) {
        return nodes[i];
      }
    }
  
    // retrieve child element at given index
    // create & insert if doesn't exist or if tags do not match
    function domChild(el, index, tag, ns) {
      var a = el.childNodes[index], b;
      if (!a || a.tagName.toLowerCase() !== tag.toLowerCase()) {
        b = a || null;
        a = domCreate(el.ownerDocument, tag, ns);
        el.insertBefore(a, b);
      }
      return a;
    }
  
    // remove all child elements at or above the given index
    function domClear(el, index) {
      var nodes = el.childNodes,
          curr = nodes.length;
      while (curr > index) el.removeChild(nodes[--curr]);
      return el;
    }
  
    // generate css class name for mark
    function cssClass(mark) {
      return 'mark-' + mark.marktype
        + (mark.role ? ' role-' + mark.role : '')
        + (mark.name ? ' ' + mark.name : '');
    }
  
    function point(event, el) {
      var rect = el.getBoundingClientRect();
      return [
        event.clientX - rect.left - (el.clientLeft || 0),
        event.clientY - rect.top - (el.clientTop || 0)
      ];
    }
  
    function resolveItem(item, event, el, origin) {
      var mark = item && item.mark,
          mdef, p;
  
      if (mark && (mdef = Marks[mark.marktype]).tip) {
        p = point(event, el);
        p[0] -= origin[0];
        p[1] -= origin[1];
        while (item = item.mark.group) {
          p[0] -= item.x || 0;
          p[1] -= item.y || 0;
        }
        item = mdef.tip(mark.items, p);
      }
  
      return item;
    }
  
    /**
     * Create a new Handler instance.
     * @param {object} [customLoader] - Optional loader instance for
     *   href URL sanitization. If not specified, a standard loader
     *   instance will be generated.
     * @param {function} [customTooltip] - Optional tooltip handler
     *   function for custom tooltip display.
     * @constructor
     */
    function Handler(customLoader, customTooltip) {
      this._active = null;
      this._handlers = {};
      this._loader = customLoader || loader();
      this._tooltip = customTooltip || defaultTooltip;
    }
  
    // The default tooltip display handler.
    // Sets the HTML title attribute on the visualization container.
    function defaultTooltip(handler, event, item, value) {
      handler.element().setAttribute('title', value || '');
    }
  
    var prototype$G = Handler.prototype;
  
    /**
     * Initialize a new Handler instance.
     * @param {DOMElement} el - The containing DOM element for the display.
     * @param {Array<number>} origin - The origin of the display, in pixels.
     *   The coordinate system will be translated to this point.
     * @param {object} [obj] - Optional context object that should serve as
     *   the "this" context for event callbacks.
     * @return {Handler} - This handler instance.
     */
    prototype$G.initialize = function(el, origin, obj) {
      this._el = el;
      this._obj = obj || null;
      return this.origin(origin);
    };
  
    /**
     * Returns the parent container element for a visualization.
     * @return {DOMElement} - The containing DOM element.
     */
    prototype$G.element = function() {
      return this._el;
    };
  
    /**
     * Returns the scene element (e.g., canvas or SVG) of the visualization
     * Subclasses must override if the first child is not the scene element.
     * @return {DOMElement} - The scene (e.g., canvas or SVG) element.
     */
    prototype$G.canvas = function() {
      return this._el && this._el.firstChild;
    };
  
    /**
     * Get / set the origin coordinates of the visualization.
     */
    prototype$G.origin = function(origin) {
      if (arguments.length) {
        this._origin = origin || [0, 0];
        return this;
      } else {
        return this._origin.slice();
      }
    };
  
    /**
     * Get / set the scenegraph root.
     */
    prototype$G.scene = function(scene) {
      if (!arguments.length) return this._scene;
      this._scene = scene;
      return this;
    };
  
    /**
     * Add an event handler. Subclasses should override this method.
     */
    prototype$G.on = function(/*type, handler*/) {};
  
    /**
     * Remove an event handler. Subclasses should override this method.
     */
    prototype$G.off = function(/*type, handler*/) {};
  
    /**
     * Utility method for finding the array index of an event handler.
     * @param {Array} h - An array of registered event handlers.
     * @param {string} type - The event type.
     * @param {function} handler - The event handler instance to find.
     * @return {number} - The handler's array index or -1 if not registered.
     */
    prototype$G._handlerIndex = function(h, type, handler) {
      for (var i = h ? h.length : 0; --i>=0;) {
        if (h[i].type === type && (!handler || h[i].handler === handler)) {
          return i;
        }
      }
      return -1;
    };
  
    /**
     * Returns an array with registered event handlers.
     * @param {string} [type] - The event type to query. Any annotations
     *   are ignored; for example, for the argument "click.foo", ".foo" will
     *   be ignored and the method returns all "click" handlers. If type is
     *   null or unspecified, this method returns handlers for all types.
     * @return {Array} - A new array containing all registered event handlers.
     */
    prototype$G.handlers = function(type) {
      var h = this._handlers, a = [], k;
      if (type) {
        a.push.apply(a, h[this.eventName(type)]);
      } else {
        for (k in h) { a.push.apply(a, h[k]); }
      }
      return a;
    };
  
    /**
     * Parses an event name string to return the specific event type.
     * For example, given "click.foo" returns "click"
     * @param {string} name - The input event type string.
     * @return {string} - A string with the event type only.
     */
    prototype$G.eventName = function(name) {
      var i = name.indexOf('.');
      return i < 0 ? name : name.slice(0,i);
    };
  
    /**
     * Handle hyperlink navigation in response to an item.href value.
     * @param {Event} event - The event triggering hyperlink navigation.
     * @param {Item} item - The scenegraph item.
     * @param {string} href - The URL to navigate to.
     */
    prototype$G.handleHref = function(event, item, href) {
      this._loader
        .sanitize(href, {context:'href'})
        .then(function(opt) {
          var e = new MouseEvent(event.type, event),
              a = domCreate(null, 'a');
          for (var name in opt) a.setAttribute(name, opt[name]);
          a.dispatchEvent(e);
        })
        .catch(function() { /* do nothing */ });
    };
  
    /**
     * Handle tooltip display in response to an item.tooltip value.
     * @param {Event} event - The event triggering tooltip display.
     * @param {Item} item - The scenegraph item.
     * @param {boolean} show - A boolean flag indicating whether
     *   to show or hide a tooltip for the given item.
     */
    prototype$G.handleTooltip = function(event, item, show) {
      if (item && item.tooltip != null) {
        item = resolveItem(item, event, this.canvas(), this._origin);
        var value = (show && item && item.tooltip) || null;
        this._tooltip.call(this._obj, this, event, item, value);
      }
    };
  
    /**
     * Returns the size of a scenegraph item and its position relative
     * to the viewport.
     * @param {Item} item - The scenegraph item.
     * @return {object} - A bounding box object (compatible with the
     *   DOMRect type) consisting of x, y, width, heigh, top, left,
     *   right, and bottom properties.
     */
    prototype$G.getItemBoundingClientRect = function(item) {
      if (!(el = this.canvas())) return;
  
      var el, rect = el.getBoundingClientRect(),
          origin = this._origin,
          itemBounds = item.bounds,
          x = itemBounds.x1 + origin[0] + rect.left,
          y = itemBounds.y1 + origin[1] + rect.top,
          w = itemBounds.width(),
          h = itemBounds.height();
  
      // translate coordinate for each parent group
      while (item.mark && (item = item.mark.group)) {
        x += item.x || 0;
        y += item.y || 0;
      }
  
      // return DOMRect-compatible bounding box
      return {
        x:      x,
        y:      y,
        width:  w,
        height: h,
        left:   x,
        top:    y,
        right:  x + w,
        bottom: y + h
      };
    };
  
    /**
     * Create a new Renderer instance.
     * @param {object} [loader] - Optional loader instance for
     *   image and href URL sanitization. If not specified, a
     *   standard loader instance will be generated.
     * @constructor
     */
    function Renderer(loader) {
      this._el = null;
      this._bgcolor = null;
      this._loader = new ResourceLoader(loader);
    }
  
    var prototype$H = Renderer.prototype;
  
    /**
     * Initialize a new Renderer instance.
     * @param {DOMElement} el - The containing DOM element for the display.
     * @param {number} width - The coordinate width of the display, in pixels.
     * @param {number} height - The coordinate height of the display, in pixels.
     * @param {Array<number>} origin - The origin of the display, in pixels.
     *   The coordinate system will be translated to this point.
     * @param {number} [scaleFactor=1] - Optional scaleFactor by which to multiply
     *   the width and height to determine the final pixel size.
     * @return {Renderer} - This renderer instance.
     */
    prototype$H.initialize = function(el, width, height, origin, scaleFactor) {
      this._el = el;
      return this.resize(width, height, origin, scaleFactor);
    };
  
    /**
     * Returns the parent container element for a visualization.
     * @return {DOMElement} - The containing DOM element.
     */
    prototype$H.element = function() {
      return this._el;
    };
  
    /**
     * Returns the scene element (e.g., canvas or SVG) of the visualization
     * Subclasses must override if the first child is not the scene element.
     * @return {DOMElement} - The scene (e.g., canvas or SVG) element.
     */
    prototype$H.canvas = function() {
      return this._el && this._el.firstChild;
    };
  
    /**
     * Get / set the background color.
     */
    prototype$H.background = function(bgcolor) {
      if (arguments.length === 0) return this._bgcolor;
      this._bgcolor = bgcolor;
      return this;
    };
  
    /**
     * Resize the display.
     * @param {number} width - The new coordinate width of the display, in pixels.
     * @param {number} height - The new coordinate height of the display, in pixels.
     * @param {Array<number>} origin - The new origin of the display, in pixels.
     *   The coordinate system will be translated to this point.
     * @param {number} [scaleFactor=1] - Optional scaleFactor by which to multiply
     *   the width and height to determine the final pixel size.
     * @return {Renderer} - This renderer instance;
     */
    prototype$H.resize = function(width, height, origin, scaleFactor) {
      this._width = width;
      this._height = height;
      this._origin = origin || [0, 0];
      this._scale = scaleFactor || 1;
      return this;
    };
  
    /**
     * Report a dirty item whose bounds should be redrawn.
     * This base class method does nothing. Subclasses that perform
     * incremental should implement this method.
     * @param {Item} item - The dirty item whose bounds should be redrawn.
     */
    prototype$H.dirty = function(/*item*/) {
    };
  
    /**
     * Render an input scenegraph, potentially with a set of dirty items.
     * This method will perform an immediate rendering with available resources.
     * The renderer may also need to perform image loading to perform a complete
     * render. This process can lead to asynchronous re-rendering of the scene
     * after this method returns. To receive notification when rendering is
     * complete, use the renderAsync method instead.
     * @param {object} scene - The root mark of a scenegraph to render.
     * @return {Renderer} - This renderer instance.
     */
    prototype$H.render = function(scene) {
      var r = this;
  
      // bind arguments into a render call, and cache it
      // this function may be subsequently called for async redraw
      r._call = function() { r._render(scene); };
  
      // invoke the renderer
      r._call();
  
      // clear the cached call for garbage collection
      // async redraws will stash their own copy
      r._call = null;
  
      return r;
    };
  
    /**
     * Internal rendering method. Renderer subclasses should override this
     * method to actually perform rendering.
     * @param {object} scene - The root mark of a scenegraph to render.
     */
    prototype$H._render = function(/*scene*/) {
      // subclasses to override
    };
  
    /**
     * Asynchronous rendering method. Similar to render, but returns a Promise
     * that resolves when all rendering is completed. Sometimes a renderer must
     * perform image loading to get a complete rendering. The returned
     * Promise will not resolve until this process completes.
     * @param {object} scene - The root mark of a scenegraph to render.
     * @return {Promise} - A Promise that resolves when rendering is complete.
     */
    prototype$H.renderAsync = function(scene) {
      var r = this.render(scene);
      return this._ready
        ? this._ready.then(function() { return r; })
        : Promise.resolve(r);
    };
  
    /**
     * Internal method for asynchronous resource loading.
     * Proxies method calls to the ImageLoader, and tracks loading
     * progress to invoke a re-render once complete.
     * @param {string} method - The method name to invoke on the ImageLoader.
     * @param {string} uri - The URI for the requested resource.
     * @return {Promise} - A Promise that resolves to the requested resource.
     */
    prototype$H._load = function(method, uri) {
      var r = this,
          p = r._loader[method](uri);
  
      if (!r._ready) {
        // re-render the scene when loading completes
        var call = r._call;
        r._ready = r._loader.ready()
          .then(function(redraw) {
            if (redraw) call();
            r._ready = null;
          });
      }
  
      return p;
    };
  
    /**
     * Sanitize a URL to include as a hyperlink in the rendered scene.
     * This method proxies a call to ImageLoader.sanitizeURL, but also tracks
     * image loading progress and invokes a re-render once complete.
     * @param {string} uri - The URI string to sanitize.
     * @return {Promise} - A Promise that resolves to the sanitized URL.
     */
    prototype$H.sanitizeURL = function(uri) {
      return this._load('sanitizeURL', uri);
    };
  
    /**
     * Requests an image to include in the rendered scene.
     * This method proxies a call to ImageLoader.loadImage, but also tracks
     * image loading progress and invokes a re-render once complete.
     * @param {string} uri - The URI string of the image.
     * @return {Promise} - A Promise that resolves to the loaded Image.
     */
    prototype$H.loadImage = function(uri) {
      return this._load('loadImage', uri);
    };
  
    var Events = [
      'keydown',
      'keypress',
      'keyup',
      'dragenter',
      'dragleave',
      'dragover',
      'mousedown',
      'mouseup',
      'mousemove',
      'mouseout',
      'mouseover',
      'click',
      'dblclick',
      'wheel',
      'mousewheel',
      'touchstart',
      'touchmove',
      'touchend'
    ];
  
    var TooltipShowEvent = 'mousemove';
  
    var TooltipHideEvent = 'mouseout';
  
    var HrefEvent = 'click';
  
    function CanvasHandler(loader, tooltip) {
      Handler.call(this, loader, tooltip);
      this._down = null;
      this._touch = null;
      this._first = true;
    }
  
    var prototype$I = inherits(CanvasHandler, Handler);
  
    prototype$I.initialize = function(el, origin, obj) {
      // add event listeners
      var canvas = this._canvas = el && domFind(el, 'canvas');
      if (canvas) {
        var that = this;
        this.events.forEach(function(type) {
          canvas.addEventListener(type, function(evt) {
            if (prototype$I[type]) {
              prototype$I[type].call(that, evt);
            } else {
              that.fire(type, evt);
            }
          });
        });
      }
  
      return Handler.prototype.initialize.call(this, el, origin, obj);
    };
  
    // return the backing canvas instance
    prototype$I.canvas = function() {
      return this._canvas;
    };
  
    // retrieve the current canvas context
    prototype$I.context = function() {
      return this._canvas.getContext('2d');
    };
  
    // supported events
    prototype$I.events = Events;
  
    // to keep old versions of firefox happy
    prototype$I.DOMMouseScroll = function(evt) {
      this.fire('mousewheel', evt);
    };
  
    function move(moveEvent, overEvent, outEvent) {
      return function(evt) {
        var a = this._active,
            p = this.pickEvent(evt);
  
        if (p === a) {
          // active item and picked item are the same
          this.fire(moveEvent, evt); // fire move
        } else {
          // active item and picked item are different
          if (!a || !a.exit) {
            // fire out for prior active item
            // suppress if active item was removed from scene
            this.fire(outEvent, evt);
          }
          this._active = p;          // set new active item
          this.fire(overEvent, evt); // fire over for new active item
          this.fire(moveEvent, evt); // fire move for new active item
        }
      };
    }
  
    function inactive(type) {
      return function(evt) {
        this.fire(type, evt);
        this._active = null;
      };
    }
  
    prototype$I.mousemove = move('mousemove', 'mouseover', 'mouseout');
    prototype$I.dragover  = move('dragover', 'dragenter', 'dragleave');
  
    prototype$I.mouseout  = inactive('mouseout');
    prototype$I.dragleave = inactive('dragleave');
  
    prototype$I.mousedown = function(evt) {
      this._down = this._active;
      this.fire('mousedown', evt);
    };
  
    prototype$I.click = function(evt) {
      if (this._down === this._active) {
        this.fire('click', evt);
        this._down = null;
      }
    };
  
    prototype$I.touchstart = function(evt) {
      this._touch = this.pickEvent(evt.changedTouches[0]);
  
      if (this._first) {
        this._active = this._touch;
        this._first = false;
      }
  
      this.fire('touchstart', evt, true);
    };
  
    prototype$I.touchmove = function(evt) {
      this.fire('touchmove', evt, true);
    };
  
    prototype$I.touchend = function(evt) {
      this.fire('touchend', evt, true);
      this._touch = null;
    };
  
    // fire an event
    prototype$I.fire = function(type, evt, touch) {
      var a = touch ? this._touch : this._active,
          h = this._handlers[type], i, len;
  
      // set event type relative to scenegraph items
      evt.vegaType = type;
  
      // handle hyperlinks and tooltips first
      if (type === HrefEvent && a && a.href) {
        this.handleHref(evt, a, a.href);
      } else if (type === TooltipShowEvent || type === TooltipHideEvent) {
        this.handleTooltip(evt, a, type !== TooltipHideEvent);
      }
  
      // invoke all registered handlers
      if (h) {
        for (i=0, len=h.length; i<len; ++i) {
          h[i].handler.call(this._obj, evt, a);
        }
      }
    };
  
    // add an event handler
    prototype$I.on = function(type, handler) {
      var name = this.eventName(type),
          h = this._handlers,
          i = this._handlerIndex(h[name], type, handler);
  
      if (i < 0) {
        (h[name] || (h[name] = [])).push({
          type:    type,
          handler: handler
        });
      }
  
      return this;
    };
  
    // remove an event handler
    prototype$I.off = function(type, handler) {
      var name = this.eventName(type),
          h = this._handlers[name],
          i = this._handlerIndex(h, type, handler);
  
      if (i >= 0) {
        h.splice(i, 1);
      }
  
      return this;
    };
  
    prototype$I.pickEvent = function(evt) {
      var p = point(evt, this._canvas),
          o = this._origin;
      return this.pick(this._scene, p[0], p[1], p[0] - o[0], p[1] - o[1]);
    };
  
    // find the scenegraph item at the current mouse position
    // x, y -- the absolute x, y mouse coordinates on the canvas element
    // gx, gy -- the relative coordinates within the current group
    prototype$I.pick = function(scene, x, y, gx, gy) {
      var g = this.context(),
          mark = Marks[scene.marktype];
      return mark.pick.call(this, g, scene, x, y, gx, gy);
    };
  
    function clip$1(context, scene) {
      var clip = scene.clip;
  
      context.save();
      context.beginPath();
  
      if (isFunction(clip)) {
        clip(context);
      } else {
        var group = scene.group;
        context.rect(0, 0, group.width || 0, group.height || 0);
      }
  
      context.clip();
    }
  
    function devicePixelRatio() {
      return typeof window !== 'undefined' ? window.devicePixelRatio || 1 : 1;
    }
  
    var pixelRatio = devicePixelRatio();
  
    function resize(canvas, width, height, origin, scaleFactor, opt) {
      var inDOM = typeof HTMLElement !== 'undefined'
        && canvas instanceof HTMLElement
        && canvas.parentNode != null;
  
      var context = canvas.getContext('2d'),
          ratio = inDOM ? pixelRatio : scaleFactor,
          key;
  
      canvas.width = width * ratio;
      canvas.height = height * ratio;
  
      for (key in opt) {
        context[key] = opt[key];
      }
  
      if (inDOM && ratio !== 1) {
        canvas.style.width = width + 'px';
        canvas.style.height = height + 'px';
      }
  
      context.pixelRatio = ratio;
      context.setTransform(
        ratio, 0, 0, ratio,
        ratio * origin[0],
        ratio * origin[1]
      );
  
      return canvas;
    }
  
    function CanvasRenderer(loader) {
      Renderer.call(this, loader);
      this._redraw = false;
      this._dirty = new Bounds();
    }
  
    var prototype$J = inherits(CanvasRenderer, Renderer),
        base = Renderer.prototype,
        tempBounds$1 = new Bounds();
  
    prototype$J.initialize = function(el, width, height, origin, scaleFactor, options) {
      this._options = options;
      this._canvas = domCanvas(1, 1, options && options.type); // instantiate a small canvas
  
      if (el) {
        domClear(el, 0).appendChild(this._canvas);
        this._canvas.setAttribute('class', 'marks');
      }
      // this method will invoke resize to size the canvas appropriately
      return base.initialize.call(this, el, width, height, origin, scaleFactor);
    };
  
    prototype$J.resize = function(width, height, origin, scaleFactor) {
      base.resize.call(this, width, height, origin, scaleFactor);
      resize(this._canvas, this._width, this._height,
        this._origin, this._scale, this._options && this._options.context);
      this._redraw = true;
      return this;
    };
  
    prototype$J.canvas = function() {
      return this._canvas;
    };
  
    prototype$J.context = function() {
      return this._canvas ? this._canvas.getContext('2d') : null;
    };
  
    prototype$J.dirty = function(item) {
      var b = translate$1(item.bounds, item.mark.group);
      this._dirty.union(b);
    };
  
    function clipToBounds(g, b, origin) {
      // expand bounds by 1 pixel, then round to pixel boundaries
      b.expand(1).round();
  
      // to avoid artifacts translate if origin has fractional pixels
      b.translate(-(origin[0] % 1), -(origin[1] % 1));
  
      // set clipping path
      g.beginPath();
      g.rect(b.x1, b.y1, b.width(), b.height());
      g.clip();
  
      return b;
    }
  
    function translate$1(bounds, group) {
      if (group == null) return bounds;
      var b = tempBounds$1.clear().union(bounds);
      for (; group != null; group = group.mark.group) {
        b.translate(group.x || 0, group.y || 0);
      }
      return b;
    }
  
    prototype$J._render = function(scene) {
      var g = this.context(),
          o = this._origin,
          w = this._width,
          h = this._height,
          b = this._dirty;
  
      // setup
      g.save();
      if (this._redraw || b.empty()) {
        this._redraw = false;
        b = null;
      } else {
        b = clipToBounds(g, b, o);
      }
  
      this.clear(-o[0], -o[1], w, h);
  
      // render
      this.draw(g, scene, b);
  
      // takedown
      g.restore();
  
      this._dirty.clear();
      return this;
    };
  
    prototype$J.draw = function(ctx, scene, bounds) {
      var mark = Marks[scene.marktype];
      if (scene.clip) clip$1(ctx, scene);
      mark.draw.call(this, ctx, scene, bounds);
      if (scene.clip) ctx.restore();
    };
  
    prototype$J.clear = function(x, y, w, h) {
      var g = this.context();
      g.clearRect(x, y, w, h);
      if (this._bgcolor != null) {
        g.fillStyle = this._bgcolor;
        g.fillRect(x, y, w, h);
      }
    };
  
    function SVGHandler(loader, tooltip) {
      Handler.call(this, loader, tooltip);
      var h = this;
      h._hrefHandler = listener(h, function(evt, item) {
        if (item && item.href) h.handleHref(evt, item, item.href);
      });
      h._tooltipHandler = listener(h, function(evt, item) {
        h.handleTooltip(evt, item, evt.type !== TooltipHideEvent);
      });
    }
  
    var prototype$K = inherits(SVGHandler, Handler);
  
    prototype$K.initialize = function(el, origin, obj) {
      var svg = this._svg;
      if (svg) {
        svg.removeEventListener(HrefEvent, this._hrefHandler);
        svg.removeEventListener(TooltipShowEvent, this._tooltipHandler);
        svg.removeEventListener(TooltipHideEvent, this._tooltipHandler);
      }
      this._svg = svg = el && domFind(el, 'svg');
      if (svg) {
        svg.addEventListener(HrefEvent, this._hrefHandler);
        svg.addEventListener(TooltipShowEvent, this._tooltipHandler);
        svg.addEventListener(TooltipHideEvent, this._tooltipHandler);
      }
      return Handler.prototype.initialize.call(this, el, origin, obj);
    };
  
    prototype$K.canvas = function() {
      return this._svg;
    };
  
    // wrap an event listener for the SVG DOM
    function listener(context, handler) {
      return function(evt) {
        var target = evt.target,
            item = target.__data__;
        evt.vegaType = evt.type;
        item = Array.isArray(item) ? item[0] : item;
        handler.call(context._obj, evt, item);
      };
    }
  
    // add an event handler
    prototype$K.on = function(type, handler) {
      var name = this.eventName(type),
          h = this._handlers,
          i = this._handlerIndex(h[name], type, handler);
  
      if (i < 0) {
        var x = {
          type:     type,
          handler:  handler,
          listener: listener(this, handler)
        };
  
        (h[name] || (h[name] = [])).push(x);
        if (this._svg) {
          this._svg.addEventListener(name, x.listener);
        }
      }
  
      return this;
    };
  
    // remove an event handler
    prototype$K.off = function(type, handler) {
      var name = this.eventName(type),
          h = this._handlers[name],
          i = this._handlerIndex(h, type, handler);
  
      if (i >= 0) {
        if (this._svg) {
          this._svg.removeEventListener(name, h[i].listener);
        }
        h.splice(i, 1);
      }
  
      return this;
    };
  
    // generate string for an opening xml tag
    // tag: the name of the xml tag
    // attr: hash of attribute name-value pairs to include
    // raw: additional raw string to include in tag markup
    function openTag(tag, attr, raw) {
      var s = '<' + tag, key, val;
      if (attr) {
        for (key in attr) {
          val = attr[key];
          if (val != null) {
            s += ' ' + key + '="' + val + '"';
          }
        }
      }
      if (raw) s += ' ' + raw;
      return s + '>';
    }
  
    // generate string for closing xml tag
    // tag: the name of the xml tag
    function closeTag(tag) {
      return '</' + tag + '>';
    }
  
    var metadata = {
      'version': '1.1',
      'xmlns': 'http://www.w3.org/2000/svg',
      'xmlns:xlink': 'http://www.w3.org/1999/xlink'
    };
  
    var styles = {
      'fill':             'fill',
      'fillOpacity':      'fill-opacity',
      'stroke':           'stroke',
      'strokeOpacity':    'stroke-opacity',
      'strokeWidth':      'stroke-width',
      'strokeCap':        'stroke-linecap',
      'strokeJoin':       'stroke-linejoin',
      'strokeDash':       'stroke-dasharray',
      'strokeDashOffset': 'stroke-dashoffset',
      'strokeMiterLimit': 'stroke-miterlimit',
      'opacity':          'opacity'
    };
  
    var styleProperties = Object.keys(styles);
  
    var ns = metadata.xmlns;
  
    function SVGRenderer(loader) {
      Renderer.call(this, loader);
      this._dirtyID = 1;
      this._dirty = [];
      this._svg = null;
      this._root = null;
      this._defs = null;
    }
  
    var prototype$L = inherits(SVGRenderer, Renderer);
    var base$1 = Renderer.prototype;
  
    prototype$L.initialize = function(el, width, height, padding) {
      if (el) {
        this._svg = domChild(el, 0, 'svg', ns);
        this._svg.setAttribute('class', 'marks');
        domClear(el, 1);
        // set the svg root group
        this._root = domChild(this._svg, 0, 'g', ns);
        domClear(this._svg, 1);
      }
  
      // create the svg definitions cache
      this._defs = {
        gradient: {},
        clipping: {}
      };
  
      // set background color if defined
      this.background(this._bgcolor);
  
      return base$1.initialize.call(this, el, width, height, padding);
    };
  
    prototype$L.background = function(bgcolor) {
      if (arguments.length && this._svg) {
        this._svg.style.setProperty('background-color', bgcolor);
      }
      return base$1.background.apply(this, arguments);
    };
  
    prototype$L.resize = function(width, height, origin, scaleFactor) {
      base$1.resize.call(this, width, height, origin, scaleFactor);
  
      if (this._svg) {
        this._svg.setAttribute('width', this._width * this._scale);
        this._svg.setAttribute('height', this._height * this._scale);
        this._svg.setAttribute('viewBox', '0 0 ' + this._width + ' ' + this._height);
        this._root.setAttribute('transform', 'translate(' + this._origin + ')');
      }
  
      this._dirty = [];
  
      return this;
    };
  
    prototype$L.canvas = function() {
      return this._svg;
    };
  
    prototype$L.svg = function() {
      if (!this._svg) return null;
  
      var attr = {
        class:   'marks',
        width:   this._width * this._scale,
        height:  this._height * this._scale,
        viewBox: '0 0 ' + this._width + ' ' + this._height
      };
      for (var key in metadata) {
        attr[key] = metadata[key];
      }
  
      var bg = !this._bgcolor ? ''
        : (openTag('rect', {
            width:  this._width,
            height: this._height,
            style:  'fill: ' + this._bgcolor + ';'
          }) + closeTag('rect'));
  
      return openTag('svg', attr) + bg + this._svg.innerHTML + closeTag('svg');
    };
  
  
    // -- Render entry point --
  
    prototype$L._render = function(scene) {
      // perform spot updates and re-render markup
      if (this._dirtyCheck()) {
        if (this._dirtyAll) this._resetDefs();
        this.draw(this._root, scene);
        domClear(this._root, 1);
      }
  
      this.updateDefs();
  
      this._dirty = [];
      ++this._dirtyID;
  
      return this;
    };
  
    // -- Manage SVG definitions ('defs') block --
  
    prototype$L.updateDefs = function() {
      var svg = this._svg,
          defs = this._defs,
          el = defs.el,
          index = 0, id;
  
      for (id in defs.gradient) {
        if (!el) defs.el = (el = domChild(svg, 0, 'defs', ns));
        index = updateGradient(el, defs.gradient[id], index);
      }
  
      for (id in defs.clipping) {
        if (!el) defs.el = (el = domChild(svg, 0, 'defs', ns));
        index = updateClipping(el, defs.clipping[id], index);
      }
  
      // clean-up
      if (el) {
        if (index === 0) {
          svg.removeChild(el);
          defs.el = null;
        } else {
          domClear(el, index);
        }
      }
    };
  
    function updateGradient(el, grad, index) {
      var i, n, stop;
  
      if (grad.gradient === 'radial') {
        // SVG radial gradients automatically transform to normalized bbox
        // coordinates, in a way that is cumbersome to replicate in canvas.
        // So we wrap the radial gradient in a pattern element, allowing us
        // to mantain a circular gradient that matches what canvas provides.
        var pt = domChild(el, index++, 'pattern', ns);
        pt.setAttribute('id', patternPrefix + grad.id);
        pt.setAttribute('viewBox', '0,0,1,1');
        pt.setAttribute('width', '100%');
        pt.setAttribute('height', '100%');
        pt.setAttribute('preserveAspectRatio', 'xMidYMid slice');
  
        pt = domChild(pt, 0, 'rect', ns);
        pt.setAttribute('width', '1');
        pt.setAttribute('height', '1');
        pt.setAttribute('fill', 'url(' + href() + '#' + grad.id + ')');
  
        el = domChild(el, index++, 'radialGradient', ns);
        el.setAttribute('id', grad.id);
        el.setAttribute('fx', grad.x1);
        el.setAttribute('fy', grad.y1);
        el.setAttribute('fr', grad.r1);
        el.setAttribute('cx', grad.x2);
        el.setAttribute('cy', grad.y2);
        el.setAttribute( 'r', grad.r2);
      } else {
        el = domChild(el, index++, 'linearGradient', ns);
        el.setAttribute('id', grad.id);
        el.setAttribute('x1', grad.x1);
        el.setAttribute('x2', grad.x2);
        el.setAttribute('y1', grad.y1);
        el.setAttribute('y2', grad.y2);
      }
  
      for (i=0, n=grad.stops.length; i<n; ++i) {
        stop = domChild(el, i, 'stop', ns);
        stop.setAttribute('offset', grad.stops[i].offset);
        stop.setAttribute('stop-color', grad.stops[i].color);
      }
      domClear(el, i);
  
      return index;
    }
  
    function updateClipping(el, clip, index) {
      var mask;
  
      el = domChild(el, index, 'clipPath', ns);
      el.setAttribute('id', clip.id);
  
      if (clip.path) {
        mask = domChild(el, 0, 'path', ns);
        mask.setAttribute('d', clip.path);
      } else {
        mask = domChild(el, 0, 'rect', ns);
        mask.setAttribute('x', 0);
        mask.setAttribute('y', 0);
        mask.setAttribute('width', clip.width);
        mask.setAttribute('height', clip.height);
      }
  
      return index + 1;
    }
  
    prototype$L._resetDefs = function() {
      var def = this._defs;
      def.gradient = {};
      def.clipping = {};
    };
  
  
    // -- Manage rendering of items marked as dirty --
  
    prototype$L.dirty = function(item) {
      if (item.dirty !== this._dirtyID) {
        item.dirty = this._dirtyID;
        this._dirty.push(item);
      }
    };
  
    prototype$L.isDirty = function(item) {
      return this._dirtyAll
        || !item._svg
        || item.dirty === this._dirtyID;
    };
  
    prototype$L._dirtyCheck = function() {
      this._dirtyAll = true;
      var items = this._dirty;
      if (!items.length) return true;
  
      var id = ++this._dirtyID,
          item, mark, type, mdef, i, n, o;
  
      for (i=0, n=items.length; i<n; ++i) {
        item = items[i];
        mark = item.mark;
  
        if (mark.marktype !== type) {
          // memoize mark instance lookup
          type = mark.marktype;
          mdef = Marks[type];
        }
  
        if (mark.zdirty && mark.dirty !== id) {
          this._dirtyAll = false;
          dirtyParents(item, id);
          mark.items.forEach(function(i) { i.dirty = id; });
        }
        if (mark.zdirty) continue; // handle in standard drawing pass
  
        if (item.exit) { // EXIT
          if (mdef.nested && mark.items.length) {
            // if nested mark with remaining points, update instead
            o = mark.items[0];
            if (o._svg) this._update(mdef, o._svg, o);
          } else if (item._svg) {
            // otherwise remove from DOM
            o = item._svg.parentNode;
            if (o) o.removeChild(item._svg);
          }
          item._svg = null;
          continue;
        }
  
        item = (mdef.nested ? mark.items[0] : item);
        if (item._update === id) continue; // already visited
  
        if (!item._svg || !item._svg.ownerSVGElement) {
          // ENTER
          this._dirtyAll = false;
          dirtyParents(item, id);
        } else {
          // IN-PLACE UPDATE
          this._update(mdef, item._svg, item);
        }
        item._update = id;
      }
      return !this._dirtyAll;
    };
  
    function dirtyParents(item, id) {
      for (; item && item.dirty !== id; item=item.mark.group) {
        item.dirty = id;
        if (item.mark && item.mark.dirty !== id) {
          item.mark.dirty = id;
        } else return;
      }
    }
  
  
    // -- Construct & maintain scenegraph to SVG mapping ---
  
    // Draw a mark container.
    prototype$L.draw = function(el, scene, prev) {
      if (!this.isDirty(scene)) return scene._svg;
  
      var renderer = this,
          svg = this._svg,
          mdef = Marks[scene.marktype],
          events = scene.interactive === false ? 'none' : null,
          isGroup = mdef.tag === 'g',
          sibling = null,
          i = 0,
          parent;
  
      parent = bind(scene, el, prev, 'g', svg);
      parent.setAttribute('class', cssClass(scene));
      if (!isGroup) {
        parent.style.setProperty('pointer-events', events);
      }
      if (scene.clip) {
        parent.setAttribute('clip-path', clip(renderer, scene, scene.group));
      } else {
        parent.removeAttribute('clip-path');
      }
  
      function process(item) {
        var dirty = renderer.isDirty(item),
            node = bind(item, parent, sibling, mdef.tag, svg);
  
        if (dirty) {
          renderer._update(mdef, node, item);
          if (isGroup) recurse(renderer, node, item);
        }
  
        sibling = node;
        ++i;
      }
  
      if (mdef.nested) {
        if (scene.items.length) process(scene.items[0]);
      } else {
        visit(scene, process);
      }
  
      domClear(parent, i);
      return parent;
    };
  
    // Recursively process group contents.
    function recurse(renderer, el, group) {
      el = el.lastChild;
      var prev, idx = 0;
  
      visit(group, function(item) {
        prev = renderer.draw(el, item, prev);
        ++idx;
      });
  
      // remove any extraneous DOM elements
      domClear(el, 1 + idx);
    }
  
    // Bind a scenegraph item to an SVG DOM element.
    // Create new SVG elements as needed.
    function bind(item, el, sibling, tag, svg) {
      var node = item._svg, doc;
  
      // create a new dom node if needed
      if (!node) {
        doc = el.ownerDocument;
        node = domCreate(doc, tag, ns);
        item._svg = node;
  
        if (item.mark) {
          node.__data__ = item;
          node.__values__ = {fill: 'default'};
  
          // if group, create background and foreground elements
          if (tag === 'g') {
            var bg = domCreate(doc, 'path', ns);
            bg.setAttribute('class', 'background');
            node.appendChild(bg);
            bg.__data__ = item;
  
            var fg = domCreate(doc, 'g', ns);
            node.appendChild(fg);
            fg.__data__ = item;
          }
        }
      }
  
      // (re-)insert if (a) not contained in SVG or (b) sibling order has changed
      if (node.ownerSVGElement !== svg || hasSiblings(item) && node.previousSibling !== sibling) {
        el.insertBefore(node, sibling ? sibling.nextSibling : el.firstChild);
      }
  
      return node;
    }
  
    function hasSiblings(item) {
      var parent = item.mark || item.group;
      return parent && parent.items.length > 1;
    }
  
  
    // -- Set attributes & styles on SVG elements ---
  
    var element = null, // temp var for current SVG element
        values = null;  // temp var for current values hash
  
    // Extra configuration for certain mark types
    var mark_extras = {
      group: function(mdef, el, item) {
        values = el.__values__; // use parent's values hash
  
        element = el.childNodes[1];
        mdef.foreground(emit, item, this);
  
        element = el.childNodes[0];
        mdef.background(emit, item, this);
  
        var value = item.mark.interactive === false ? 'none' : null;
        if (value !== values.events) {
          element.style.setProperty('pointer-events', value);
          values.events = value;
        }
      },
      text: function(mdef, el, item) {
        var value;
  
        value = textValue(item);
        if (value !== values.text) {
          el.textContent = value;
          values.text = value;
        }
  
        setStyle(el, 'font-family', fontFamily(item));
        setStyle(el, 'font-size', fontSize(item) + 'px');
        setStyle(el, 'font-style', item.fontStyle);
        setStyle(el, 'font-variant', item.fontVariant);
        setStyle(el, 'font-weight', item.fontWeight);
      }
    };
  
    function setStyle(el, name, value) {
      if (value !== values[name]) {
        if (value == null) {
          el.style.removeProperty(name);
        } else {
          el.style.setProperty(name, value + '');
        }
        values[name] = value;
      }
    }
  
    prototype$L._update = function(mdef, el, item) {
      // set dom element and values cache
      // provides access to emit method
      element = el;
      values = el.__values__;
  
      // apply svg attributes
      mdef.attr(emit, item, this);
  
      // some marks need special treatment
      var extra = mark_extras[mdef.type];
      if (extra) extra.call(this, mdef, el, item);
  
      // apply svg css styles
      // note: element may be modified by 'extra' method
      this.style(element, item);
    };
  
    function emit(name, value, ns) {
      // early exit if value is unchanged
      if (value === values[name]) return;
  
      if (value != null) {
        // if value is provided, update DOM attribute
        if (ns) {
          element.setAttributeNS(ns, name, value);
        } else {
          element.setAttribute(name, value);
        }
      } else {
        // else remove DOM attribute
        if (ns) {
          element.removeAttributeNS(ns, name);
        } else {
          element.removeAttribute(name);
        }
      }
  
      // note current value for future comparison
      values[name] = value;
    }
  
    prototype$L.style = function(el, o) {
      if (o == null) return;
      var i, n, prop, name, value;
  
      for (i=0, n=styleProperties.length; i<n; ++i) {
        prop = styleProperties[i];
        value = o[prop];
  
        if (prop === 'font') {
          value = fontFamily(o);
        }
  
        if (value === values[prop]) continue;
  
        name = styles[prop];
        if (value == null) {
          if (name === 'fill') {
            el.style.setProperty(name, 'none');
          } else {
            el.style.removeProperty(name);
          }
        } else {
          if (isGradient(value)) {
            value = gradientRef(value, this._defs.gradient, href());
          }
          el.style.setProperty(name, value + '');
        }
  
        values[prop] = value;
      }
    };
  
    function href() {
      var loc;
      return typeof window === 'undefined' ? ''
        : (loc = window.location).hash ? loc.href.slice(0, -loc.hash.length)
        : loc.href;
    }
  
    function SVGStringRenderer(loader) {
      Renderer.call(this, loader);
  
      this._text = {
        head: '',
        bg:   '',
        root: '',
        foot: '',
        defs: '',
        body: ''
      };
  
      this._defs = {
        gradient: {},
        clipping: {}
      };
    }
  
    var prototype$M = inherits(SVGStringRenderer, Renderer);
    var base$2 = Renderer.prototype;
  
    prototype$M.resize = function(width, height, origin, scaleFactor) {
      base$2.resize.call(this, width, height, origin, scaleFactor);
      var o = this._origin,
          t = this._text;
  
      var attr = {
        class:   'marks',
        width:   this._width * this._scale,
        height:  this._height * this._scale,
        viewBox: '0 0 ' + this._width + ' ' + this._height
      };
      for (var key in metadata) {
        attr[key] = metadata[key];
      }
  
      t.head = openTag('svg', attr);
  
      var bg = this._bgcolor;
      if (bg === 'transparent' || bg === 'none') bg = null;
  
      if (bg) {
        t.bg = openTag('rect', {
          width:  this._width,
          height: this._height,
          style:  'fill: ' + bg + ';'
        }) + closeTag('rect');
      } else {
        t.bg = '';
      }
  
      t.root = openTag('g', {
        transform: 'translate(' + o + ')'
      });
  
      t.foot = closeTag('g') + closeTag('svg');
  
      return this;
    };
  
    prototype$M.background = function() {
      var rv = base$2.background.apply(this, arguments);
      if (arguments.length && this._text.head) {
        this.resize(this._width, this._height, this._origin, this._scale);
      }
      return rv;
    };
  
    prototype$M.svg = function() {
      var t = this._text;
      return t.head + t.bg + t.defs + t.root + t.body + t.foot;
    };
  
    prototype$M._render = function(scene) {
      this._text.body = this.mark(scene);
      this._text.defs = this.buildDefs();
      return this;
    };
  
    prototype$M.buildDefs = function() {
      var all = this._defs,
          defs = '',
          i, id, def, tag, stops;
  
      for (id in all.gradient) {
        def = all.gradient[id];
        stops = def.stops;
  
        if (def.gradient === 'radial') {
          // SVG radial gradients automatically transform to normalized bbox
          // coordinates, in a way that is cumbersome to replicate in canvas.
          // So we wrap the radial gradient in a pattern element, allowing us
          // to mantain a circular gradient that matches what canvas provides.
  
          defs += openTag(tag = 'pattern', {
            id: patternPrefix + id,
            viewBox: '0,0,1,1',
            width: '100%',
            height: '100%',
            preserveAspectRatio: 'xMidYMid slice'
          });
  
          defs += openTag('rect', {
            width: '1',
            height: '1',
            fill: 'url(#' + id + ')'
          }) + closeTag('rect');
  
          defs += closeTag(tag);
  
          defs += openTag(tag = 'radialGradient', {
            id: id,
            fx: def.x1,
            fy: def.y1,
            fr: def.r1,
            cx: def.x2,
            cy: def.y2,
             r: def.r2
          });
        } else {
          defs += openTag(tag = 'linearGradient', {
            id: id,
            x1: def.x1,
            x2: def.x2,
            y1: def.y1,
            y2: def.y2
          });
        }
  
        for (i=0; i<stops.length; ++i) {
          defs += openTag('stop', {
            offset: stops[i].offset,
            'stop-color': stops[i].color
          }) + closeTag('stop');
        }
  
        defs += closeTag(tag);
      }
  
      for (id in all.clipping) {
        def = all.clipping[id];
  
        defs += openTag('clipPath', {id: id});
  
        if (def.path) {
          defs += openTag('path', {
            d: def.path
          }) + closeTag('path');
        } else {
          defs += openTag('rect', {
            x: 0,
            y: 0,
            width: def.width,
            height: def.height
          }) + closeTag('rect');
        }
  
        defs += closeTag('clipPath');
      }
  
      return (defs.length > 0) ? openTag('defs') + defs + closeTag('defs') : '';
    };
  
    var object;
  
    function emit$1(name, value, ns, prefixed) {
      object[prefixed || name] = value;
    }
  
    prototype$M.attributes = function(attr, item) {
      object = {};
      attr(emit$1, item, this);
      return object;
    };
  
    prototype$M.href = function(item) {
      var that = this,
          href = item.href,
          attr;
  
      if (href) {
        if (attr = that._hrefs && that._hrefs[href]) {
          return attr;
        } else {
          that.sanitizeURL(href).then(function(attr) {
            // rewrite to use xlink namespace
            // note that this will be deprecated in SVG 2.0
            attr['xlink:href'] = attr.href;
            attr.href = null;
            (that._hrefs || (that._hrefs = {}))[href] = attr;
          });
        }
      }
      return null;
    };
  
    prototype$M.mark = function(scene) {
      var renderer = this,
          mdef = Marks[scene.marktype],
          tag  = mdef.tag,
          defs = this._defs,
          str = '',
          style;
  
      if (tag !== 'g' && scene.interactive === false) {
        style = 'style="pointer-events: none;"';
      }
  
      // render opening group tag
      str += openTag('g', {
        'class': cssClass(scene),
        'clip-path': scene.clip ? clip(renderer, scene, scene.group) : null
      }, style);
  
      // render contained elements
      function process(item) {
        var href = renderer.href(item);
        if (href) str += openTag('a', href);
  
        style = (tag !== 'g') ? applyStyles(item, scene, tag, defs) : null;
        str += openTag(tag, renderer.attributes(mdef.attr, item), style);
  
        if (tag === 'text') {
          str += escape_text(textValue(item));
        } else if (tag === 'g') {
          str += openTag('path', renderer.attributes(mdef.background, item),
            applyStyles(item, scene, 'bgrect', defs)) + closeTag('path');
  
          str += openTag('g', renderer.attributes(mdef.foreground, item))
            + renderer.markGroup(item)
            + closeTag('g');
        }
  
        str += closeTag(tag);
        if (href) str += closeTag('a');
      }
  
      if (mdef.nested) {
        if (scene.items && scene.items.length) process(scene.items[0]);
      } else {
        visit(scene, process);
      }
  
      // render closing group tag
      return str + closeTag('g');
    };
  
    prototype$M.markGroup = function(scene) {
      var renderer = this,
          str = '';
  
      visit(scene, function(item) {
        str += renderer.mark(item);
      });
  
      return str;
    };
  
    function applyStyles(o, mark, tag, defs) {
      if (o == null) return '';
      var i, n, prop, name, value, s = '';
  
      if (tag === 'bgrect' && mark.interactive === false) {
        s += 'pointer-events: none; ';
      }
  
      if (tag === 'text') {
        s += 'font-family: ' + fontFamily(o) + '; ';
        s += 'font-size: ' + fontSize(o) + 'px; ';
        if (o.fontStyle) s += 'font-style: ' + o.fontStyle + '; ';
        if (o.fontVariant) s += 'font-variant: ' + o.fontVariant + '; ';
        if (o.fontWeight) s += 'font-weight: ' + o.fontWeight + '; ';
      }
  
      for (i=0, n=styleProperties.length; i<n; ++i) {
        prop = styleProperties[i];
        name = styles[prop];
        value = o[prop];
  
        if (value == null) {
          if (name === 'fill') {
            s += 'fill: none; ';
          }
        } else if (value === 'transparent' && (name === 'fill' || name === 'stroke')) {
          // transparent is not a legal SVG value, so map to none instead
          s += name + ': none; ';
        } else {
          if (isGradient(value)) {
            value = gradientRef(value, defs.gradient, '');
          }
          s += name + ': ' + value + '; ';
        }
      }
  
      return s ? 'style="' + s.trim() + '"' : null;
    }
  
    function escape_text(s) {
      return s.replace(/&/g, '&amp;')
              .replace(/</g, '&lt;')
              .replace(/>/g, '&gt;');
    }
  
    var Canvas = 'canvas';
    var PNG = 'png';
    var SVG = 'svg';
    var None$2 = 'none';
  
    var RenderType = {
      Canvas: Canvas,
      PNG:    PNG,
      SVG:    SVG,
      None:   None$2
    };
  
    var modules = {};
  
    modules[Canvas] = modules[PNG] = {
      renderer: CanvasRenderer,
      headless: CanvasRenderer,
      handler:  CanvasHandler
    };
  
    modules[SVG] = {
      renderer: SVGRenderer,
      headless: SVGStringRenderer,
      handler:  SVGHandler
    };
  
    modules[None$2] = {};
  
    function renderModule(name, _) {
      name = String(name || '').toLowerCase();
      if (arguments.length > 1) {
        modules[name] = _;
        return this;
      } else {
        return modules[name];
      }
    }
  
    function intersect(scene, bounds, filter) {
      const hits = [], // intersection results
            box = new Bounds().union(bounds), // defensive copy
            type = scene.marktype;
  
      return type ? intersectMark(scene, box, filter, hits)
        : type === 'group' ? intersectGroup(scene, box, filter, hits)
        : error('Intersect scene must be mark node or group item.');
    }
  
    function intersectMark(mark, box, filter, hits) {
      if (visitMark(mark, box, filter)) {
        const items = mark.items,
              type = mark.marktype,
              n = items.length;
  
        let i = 0;
  
        if (type === 'group') {
          for (; i<n; ++i) {
            intersectGroup(items[i], box, filter, hits);
          }
        } else {
          for (const test = Marks[type].isect; i<n; ++i) {
            let item = items[i];
            if (intersectItem(item, box, test)) hits.push(item);
          }
        }
      }
      return hits;
    }
  
    function visitMark(mark, box, filter) {
      // process if bounds intersect and if
      // (1) mark is a group mark (so we must recurse), or
      // (2) mark is interactive and passes filter
      return mark.bounds && box.intersects(mark.bounds) && (
        mark.marktype === 'group' ||
        mark.interactive !== false && (!filter || filter(mark))
      );
    }
  
    function intersectGroup(group, box, filter, hits) {
      // test intersect against group
      // skip groups by default unless filter says otherwise
      if ((filter && filter(group.mark)) &&
          intersectItem(group, box, Marks.group.isect)) {
        hits.push(group);
      }
  
      // recursively test children marks
      // translate box to group coordinate space
      const marks = group.items,
            n = marks && marks.length;
  
      if (n) {
        const x = group.x || 0,
              y = group.y || 0;
        box.translate(-x, -y);
        for (let i=0; i<n; ++i) {
          intersectMark(marks[i], box, filter, hits);
        }
        box.translate(x, y);
      }
  
      return hits;
    }
  
    function intersectItem(item, box, test) {
      // test bounds enclosure, bounds intersection, then detailed test
      const bounds = item.bounds;
      return box.encloses(bounds) || (box.intersects(bounds) && test(item, box));
    }
  
    var clipBounds = new Bounds();
  
    function boundClip(mark) {
      var clip = mark.clip;
  
      if (isFunction(clip)) {
        clip(context(clipBounds.clear()));
      } else if (clip) {
        clipBounds.set(0, 0, mark.group.width, mark.group.height);
      } else return;
  
      mark.bounds.intersect(clipBounds);
    }
  
    var TOLERANCE = 1e-9;
  
    function sceneEqual(a, b, key) {
      return (a === b) ? true
        : (key === 'path') ? pathEqual(a, b)
        : (a instanceof Date && b instanceof Date) ? +a === +b
        : (isNumber(a) && isNumber(b)) ? Math.abs(a - b) <= TOLERANCE
        : (!a || !b || !isObject(a) && !isObject(b)) ? a == b
        : (a == null || b == null) ? false
        : objectEqual(a, b);
    }
  
    function pathEqual(a, b) {
      return sceneEqual(pathParse(a), pathParse(b));
    }
  
    function objectEqual(a, b) {
      var ka = Object.keys(a),
          kb = Object.keys(b),
          key, i;
  
      if (ka.length !== kb.length) return false;
  
      ka.sort();
      kb.sort();
  
      for (i = ka.length - 1; i >= 0; i--) {
        if (ka[i] != kb[i]) return false;
      }
  
      for (i = ka.length - 1; i >= 0; i--) {
        key = ka[i];
        if (!sceneEqual(a[key], b[key], key)) return false;
      }
  
      return typeof a === typeof b;
    }
  
    /**
     * Calculate bounding boxes for scenegraph items.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {object} params.mark - The scenegraph mark instance to bound.
     */
    function Bound(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$N = inherits(Bound, Transform);
  
    prototype$N.transform = function(_, pulse) {
      var view = pulse.dataflow,
          mark = _.mark,
          type = mark.marktype,
          entry = Marks[type],
          bound = entry.bound,
          markBounds = mark.bounds, rebound;
  
      if (entry.nested) {
        // multi-item marks have a single bounds instance
        if (mark.items.length) view.dirty(mark.items[0]);
        markBounds = boundItem$1(mark, bound);
        mark.items.forEach(function(item) {
          item.bounds.clear().union(markBounds);
        });
      }
  
      else if (type === Group || _.modified()) {
        // operator parameters modified -> re-bound all items
        // updates group bounds in response to modified group content
        pulse.visit(pulse.MOD, function(item) { view.dirty(item); });
        markBounds.clear();
        mark.items.forEach(function(item) {
          markBounds.union(boundItem$1(item, bound));
        });
  
        // force reflow for legends to propagate any layout changes
        // suppress other types to prevent overall layout jumpiness
        if (mark.role === LegendRole) pulse.reflow();
      }
  
      else {
        // incrementally update bounds, re-bound mark as needed
        rebound = pulse.changed(pulse.REM);
  
        pulse.visit(pulse.ADD, function(item) {
          markBounds.union(boundItem$1(item, bound));
        });
  
        pulse.visit(pulse.MOD, function(item) {
          rebound = rebound || markBounds.alignsWith(item.bounds);
          view.dirty(item);
          markBounds.union(boundItem$1(item, bound));
        });
  
        if (rebound) {
          markBounds.clear();
          mark.items.forEach(function(item) { markBounds.union(item.bounds); });
        }
      }
  
      // ensure mark bounds do not exceed any clipping region
      boundClip(mark);
  
      return pulse.modifies('bounds');
    };
  
    function boundItem$1(item, bound, opt) {
      return bound(item.bounds.clear(), item, opt);
    }
  
    var COUNTER_NAME = ':vega_identifier:';
  
    /**
     * Adds a unique identifier to all added tuples.
     * This transform creates a new signal that serves as an id counter.
     * As a result, the id counter is shared across all instances of this
     * transform, generating unique ids across multiple data streams. In
     * addition, this signal value can be included in a snapshot of the
     * dataflow state, enabling correct resumption of id allocation.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {string} params.as - The field name for the generated identifier.
     */
    function Identifier(params) {
      Transform.call(this, 0, params);
    }
  
    Identifier.Definition = {
      "type": "Identifier",
      "metadata": {"modifies": true},
      "params": [
        { "name": "as", "type": "string", "required": true }
      ]
    };
  
    var prototype$O = inherits(Identifier, Transform);
  
    prototype$O.transform = function(_, pulse) {
      var counter = getCounter(pulse.dataflow),
          id = counter.value,
          as = _.as;
  
      pulse.visit(pulse.ADD, function(t) {
        if (!t[as]) t[as] = ++id;
      });
  
      counter.set(this.value = id);
      return pulse;
    };
  
    function getCounter(view) {
      var counter = view._signals[COUNTER_NAME];
      if (!counter) {
        view._signals[COUNTER_NAME] = (counter = view.add(0));
      }
      return counter;
    }
  
    /**
     * Bind scenegraph items to a scenegraph mark instance.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {object} params.markdef - The mark definition for creating the mark.
     *   This is an object of legal scenegraph mark properties which *must* include
     *   the 'marktype' property.
     */
    function Mark(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$P = inherits(Mark, Transform);
  
    prototype$P.transform = function(_, pulse) {
      var mark = this.value;
  
      // acquire mark on first invocation, bind context and group
      if (!mark) {
        mark = pulse.dataflow.scenegraph().mark(_.markdef, lookup$1(_), _.index);
        mark.group.context = _.context;
        if (!_.context.group) _.context.group = mark.group;
        mark.source = this;
        mark.clip = _.clip;
        mark.interactive = _.interactive;
        this.value = mark;
      }
  
      // initialize entering items
      var Init = mark.marktype === Group ? GroupItem : Item;
      pulse.visit(pulse.ADD, function(item) { Init.call(item, mark); });
  
      // update clipping and/or interactive status
      if (_.modified('clip') || _.modified('interactive')) {
        mark.clip = _.clip;
        mark.interactive = !!_.interactive;
        mark.zdirty = true; // force scenegraph re-eval
        pulse.reflow();
      }
  
      // bind items array to scenegraph mark
      mark.items = pulse.source;
      return pulse;
    };
  
    function lookup$1(_) {
      var g = _.groups, p = _.parent;
      return g && g.size === 1 ? g.get(Object.keys(g.object)[0])
        : g && p ? g.lookup(p)
        : null;
    }
  
    /**
     * Analyze items for overlap, changing opacity to hide items with
     * overlapping bounding boxes. This transform will preserve at least
     * two items (e.g., first and last) even if overlap persists.
     * @param {object} params - The parameters for this operator.
     * @param {function(*,*): number} [params.sort] - A comparator
     *   function for sorting items.
     * @param {object} [params.method] - The overlap removal method to apply.
     *   One of 'parity' (default, hide every other item until there is no
     *   more overlap) or 'greedy' (sequentially scan and hide and items that
     *   overlap with the last visible item).
     * @param {object} [params.boundScale] - A scale whose range should be used
     *   to bound the items. Items exceeding the bounds of the scale range
     *   will be treated as overlapping. If null or undefined, no bounds check
     *   will be applied.
     * @param {object} [params.boundOrient] - The orientation of the scale
     *   (top, bottom, left, or right) used to bound items. This parameter is
     *   ignored if boundScale is null or undefined.
     * @param {object} [params.boundTolerance] - The tolerance in pixels for
     *   bound inclusion testing (default 1). This specifies by how many pixels
     *   an item's bounds may exceed the scale range bounds and not be culled.
     * @constructor
     */
    function Overlap(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$Q = inherits(Overlap, Transform);
  
    var methods = {
      parity: function(items) {
        return items.filter((item, i) => i % 2 ? (item.opacity = 0) : 1);
      },
      greedy: function(items, sep) {
        var a;
        return items.filter((b, i) => {
          if (!i || !intersect$1(a.bounds, b.bounds, sep)) {
            a = b;
            return 1;
          } else {
            return b.opacity = 0;
          }
        });
      }
    };
  
    // compute bounding box intersection
    // including padding pixels of separation
    function intersect$1(a, b, sep) {
      return sep > Math.max(
        b.x1 - a.x2,
        a.x1 - b.x2,
        b.y1 - a.y2,
        a.y1 - b.y2
      );
    }
  
    function hasOverlap(items, pad) {
      for (var i=1, n=items.length, a=items[0].bounds, b; i<n; a=b, ++i) {
        if (intersect$1(a, b = items[i].bounds, pad)) return true;
      }
    }
  
    function hasBounds(item) {
      var b = item.bounds;
      return b.width() > 1 && b.height() > 1;
    }
  
    function boundTest(scale, orient, tolerance) {
      var range = scale.range(),
          b = new Bounds();
  
      if (orient === Top || orient === Bottom) {
        b.set(range[0], -Infinity, range[1], +Infinity);
      } else {
        b.set(-Infinity, range[0], +Infinity, range[1]);
      }
      b.expand(tolerance || 1);
  
      return item => b.encloses(item.bounds);
    }
  
    // reset all items to be fully opaque
    function reset(source) {
      source.forEach(item => item.opacity = 1);
      return source;
    }
  
    // add all tuples to mod, fork pulse if parameters were modified
    // fork prevents cross-stream tuple pollution (e.g., pulse from scale)
    function reflow(pulse, _) {
      return pulse.reflow(_.modified()).modifies('opacity');
    }
  
    prototype$Q.transform = function(_, pulse) {
      var reduce = methods[_.method] || methods.parity,
          source = pulse.materialize(pulse.SOURCE).source,
          sep = _.separation || 0,
          items, test, bounds;
  
      if (!source || !source.length) return;
  
      if (!_.method) {
        // early exit if method is falsy
        if (_.modified('method')) {
          reset(source);
          pulse = reflow(pulse, _);
        }
        return pulse;
      }
  
      if (_.sort) {
        source = source.slice().sort(_.sort);
      }
  
      // skip labels with no content
      source = source.filter(hasBounds);
  
      items = reset(source);
      pulse = reflow(pulse, _);
  
      if (items.length >= 3 && hasOverlap(items, sep)) {
        do {
          items = reduce(items, sep);
        } while (items.length >= 3 && hasOverlap(items, sep));
  
        if (items.length < 3 && !peek(source).opacity) {
          if (items.length > 1) peek(items).opacity = 0;
          peek(source).opacity = 1;
        }
      }
  
      if (_.boundScale && _.boundTolerance >= 0) {
        test = boundTest(_.boundScale, _.boundOrient, +_.boundTolerance);
        source.forEach(item => {
          if (!test(item)) item.opacity = 0;
        });
      }
  
      // re-calculate mark bounds
      bounds = items[0].mark.bounds.clear();
      source.forEach(item => {
        if (item.opacity) bounds.union(item.bounds);
      });
  
      return pulse;
    };
  
    /**
     * Queue modified scenegraph items for rendering.
     * @constructor
     */
    function Render(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$R = inherits(Render, Transform);
  
    prototype$R.transform = function(_, pulse) {
      var view = pulse.dataflow;
  
      pulse.visit(pulse.ALL, function(item) { view.dirty(item); });
  
      // set z-index dirty flag as needed
      if (pulse.fields && pulse.fields['zindex']) {
        var item = pulse.source && pulse.source[0];
        if (item) item.mark.zdirty = true;
      }
    };
  
    const tempBounds$2 = new Bounds();
  
    function set(item, property, value) {
      return item[property] === value ? 0
        : (item[property] = value, 1);
    }
  
    const AxisOffset = 0.5;
  
    function isYAxis(mark) {
      var orient = mark.items[0].datum.orient;
      return orient === Left || orient === Right;
    }
  
    function axisIndices(datum) {
      var index = +datum.grid;
      return [
        datum.ticks  ? index++ : -1, // ticks index
        datum.labels ? index++ : -1, // labels index
        index + (+datum.domain)      // title index
      ];
    }
  
    function axisLayout(view, axis, width, height) {
      var item = axis.items[0],
          datum = item.datum,
          orient = datum.orient,
          indices = axisIndices(datum),
          range = item.range,
          offset = item.offset,
          position = item.position,
          minExtent = item.minExtent,
          maxExtent = item.maxExtent,
          title = datum.title && item.items[indices[2]].items[0],
          titlePadding = item.titlePadding,
          bounds = item.bounds,
          x = 0, y = 0, i, s;
  
      tempBounds$2.clear().union(bounds);
      bounds.clear();
      if ((i=indices[0]) > -1) bounds.union(item.items[i].bounds);
      if ((i=indices[1]) > -1) bounds.union(item.items[i].bounds);
  
      // position axis group and title
      switch (orient) {
        case Top:
          x = position || 0;
          y = -offset;
          s = Math.max(minExtent, Math.min(maxExtent, -bounds.y1));
          if (title) s = axisTitleLayout(title, s, titlePadding, 0, -1, bounds);
          bounds.add(0, -s).add(range, 0);
          break;
        case Left:
          x = -offset;
          y = position || 0;
          s = Math.max(minExtent, Math.min(maxExtent, -bounds.x1));
          if (title) s = axisTitleLayout(title, s, titlePadding, 1, -1, bounds);
          bounds.add(-s, 0).add(0, range);
          break;
        case Right:
          x = width + offset;
          y = position || 0;
          s = Math.max(minExtent, Math.min(maxExtent, bounds.x2));
          if (title) s = axisTitleLayout(title, s, titlePadding, 1, 1, bounds);
          bounds.add(0, 0).add(s, range);
          break;
        case Bottom:
          x = position || 0;
          y = height + offset;
          s = Math.max(minExtent, Math.min(maxExtent, bounds.y2));
          if (title) s = axisTitleLayout(title, s, titlePadding, 0, 1, bounds);
          bounds.add(0, 0).add(range, s);
          break;
        default:
          x = item.x;
          y = item.y;
      }
  
      // update bounds
      boundStroke(bounds.translate(x, y), item);
  
      if (set(item, 'x', x + AxisOffset) | set(item, 'y', y + AxisOffset)) {
        item.bounds = tempBounds$2;
        view.dirty(item);
        item.bounds = bounds;
        view.dirty(item);
      }
  
      return item.mark.bounds.clear().union(bounds);
    }
  
    function axisTitleLayout(title, offset, pad, isYAxis, sign, bounds) {
      var b = title.bounds, dx = 0, dy = 0;
  
      if (title.auto) {
        offset += pad;
  
        isYAxis
          ? dx = (title.x || 0) - (title.x = sign * offset)
          : dy = (title.y || 0) - (title.y = sign * offset);
  
        b.translate(-dx, -dy);
        title.mark.bounds.set(b.x1, b.y1, b.x2, b.y2);
  
        if (isYAxis) {
          bounds.add(0, b.y1).add(0, b.y2);
          offset += b.width();
        } else {
          bounds.add(b.x1, 0).add(b.x2, 0);
          offset += b.height();
        }
      } else {
        bounds.union(b);
      }
  
      return offset;
    }
  
    function gridLayoutGroups(group) {
      var groups = group.items,
          n = groups.length,
          i = 0, mark, items;
  
      var views = {
        marks:      [],
        rowheaders: [],
        rowfooters: [],
        colheaders: [],
        colfooters: [],
        rowtitle: null,
        coltitle: null
      };
  
      // layout axes, gather legends, collect bounds
      for (; i<n; ++i) {
        mark = groups[i];
        items = mark.items;
        if (mark.marktype === Group) {
          switch (mark.role) {
            case AxisRole:
            case LegendRole:
              break;
            case RowHeader: views.rowheaders.push(...items); break;
            case RowFooter: views.rowfooters.push(...items); break;
            case ColHeader: views.colheaders.push(...items); break;
            case ColFooter: views.colfooters.push(...items); break;
            case RowTitle:  views.rowtitle = items[0]; break;
            case ColTitle:  views.coltitle = items[0]; break;
            default:        views.marks.push(...items);
          }
        }
      }
  
      return views;
    }
  
    function bboxFlush(item) {
      return new Bounds().set(0, 0, item.width || 0, item.height || 0);
    }
  
    function bboxFull(item) {
      var b = item.bounds.clone();
      return b.empty()
        ? b.set(0, 0, 0, 0)
        : b.translate(-(item.x || 0), -(item.y || 0));
    }
  
    function get$2(opt, key, d) {
      var v = isObject(opt) ? opt[key] : opt;
      return v != null ? v : (d !== undefined ? d : 0);
    }
  
    function offsetValue(v) {
      return v < 0 ? Math.ceil(-v) : 0;
    }
  
    function gridLayout(view, groups, opt) {
      var dirty = !opt.nodirty,
          bbox = opt.bounds === Flush ? bboxFlush : bboxFull,
          bounds = tempBounds$2.set(0, 0, 0, 0),
          alignCol = get$2(opt.align, Column),
          alignRow = get$2(opt.align, Row),
          padCol = get$2(opt.padding, Column),
          padRow = get$2(opt.padding, Row),
          ncols = opt.columns || groups.length,
          nrows = ncols < 0 ? 1 : Math.ceil(groups.length / ncols),
          n = groups.length,
          xOffset = Array(n), xExtent = Array(ncols), xMax = 0,
          yOffset = Array(n), yExtent = Array(nrows), yMax = 0,
          dx = Array(n), dy = Array(n), boxes = Array(n),
          m, i, c, r, b, g, px, py, x, y, offset;
  
      for (i=0; i<ncols; ++i) xExtent[i] = 0;
      for (i=0; i<nrows; ++i) yExtent[i] = 0;
  
      // determine offsets for each group
      for (i=0; i<n; ++i) {
        g = groups[i];
        b = boxes[i] = bbox(g);
        g.x = g.x || 0; dx[i] = 0;
        g.y = g.y || 0; dy[i] = 0;
        c = i % ncols;
        r = ~~(i / ncols);
        xMax = Math.max(xMax, px = Math.ceil(b.x2));
        yMax = Math.max(yMax, py = Math.ceil(b.y2));
        xExtent[c] = Math.max(xExtent[c], px);
        yExtent[r] = Math.max(yExtent[r], py);
        xOffset[i] = padCol + offsetValue(b.x1);
        yOffset[i] = padRow + offsetValue(b.y1);
        if (dirty) view.dirty(groups[i]);
      }
  
      // set initial alignment offsets
      for (i=0; i<n; ++i) {
        if (i % ncols === 0) xOffset[i] = 0;
        if (i < ncols) yOffset[i] = 0;
      }
  
      // enforce column alignment constraints
      if (alignCol === Each) {
        for (c=1; c<ncols; ++c) {
          for (offset=0, i=c; i<n; i += ncols) {
            if (offset < xOffset[i]) offset = xOffset[i];
          }
          for (i=c; i<n; i += ncols) {
            xOffset[i] = offset + xExtent[c-1];
          }
        }
      } else if (alignCol === All) {
        for (offset=0, i=0; i<n; ++i) {
          if (i % ncols && offset < xOffset[i]) offset = xOffset[i];
        }
        for (i=0; i<n; ++i) {
          if (i % ncols) xOffset[i] = offset + xMax;
        }
      } else {
        for (alignCol=false, c=1; c<ncols; ++c) {
          for (i=c; i<n; i += ncols) {
            xOffset[i] += xExtent[c-1];
          }
        }
      }
  
      // enforce row alignment constraints
      if (alignRow === Each) {
        for (r=1; r<nrows; ++r) {
          for (offset=0, i=r*ncols, m=i+ncols; i<m; ++i) {
            if (offset < yOffset[i]) offset = yOffset[i];
          }
          for (i=r*ncols; i<m; ++i) {
            yOffset[i] = offset + yExtent[r-1];
          }
        }
      } else if (alignRow === All) {
        for (offset=0, i=ncols; i<n; ++i) {
          if (offset < yOffset[i]) offset = yOffset[i];
        }
        for (i=ncols; i<n; ++i) {
          yOffset[i] = offset + yMax;
        }
      } else {
        for (alignRow=false, r=1; r<nrows; ++r) {
          for (i=r*ncols, m=i+ncols; i<m; ++i) {
            yOffset[i] += yExtent[r-1];
          }
        }
      }
  
      // perform horizontal grid layout
      for (x=0, i=0; i<n; ++i) {
        x = xOffset[i] + (i % ncols ? x : 0);
        dx[i] += x - groups[i].x;
      }
  
      // perform vertical grid layout
      for (c=0; c<ncols; ++c) {
        for (y=0, i=c; i<n; i += ncols) {
          y += yOffset[i];
          dy[i] += y - groups[i].y;
        }
      }
  
      // perform horizontal centering
      if (alignCol && get$2(opt.center, Column) && nrows > 1) {
        for (i=0; i<n; ++i) {
          b = alignCol === All ? xMax : xExtent[i % ncols];
          x = b - boxes[i].x2 - groups[i].x - dx[i];
          if (x > 0) dx[i] += x / 2;
        }
      }
  
      // perform vertical centering
      if (alignRow && get$2(opt.center, Row) && ncols !== 1) {
        for (i=0; i<n; ++i) {
          b = alignRow === All ? yMax : yExtent[~~(i / ncols)];
          y = b - boxes[i].y2 - groups[i].y - dy[i];
          if (y > 0) dy[i] += y / 2;
        }
      }
  
      // position grid relative to anchor
      for (i=0; i<n; ++i) {
        bounds.union(boxes[i].translate(dx[i], dy[i]));
      }
      x = get$2(opt.anchor, X);
      y = get$2(opt.anchor, Y);
      switch (get$2(opt.anchor, Column)) {
        case End:    x -= bounds.width(); break;
        case Middle: x -= bounds.width() / 2;
      }
      switch (get$2(opt.anchor, Row)) {
        case End:    y -= bounds.height(); break;
        case Middle: y -= bounds.height() / 2;
      }
      x = Math.round(x);
      y = Math.round(y);
  
      // update mark positions, bounds, dirty
      bounds.clear();
      for (i=0; i<n; ++i) {
        groups[i].mark.bounds.clear();
      }
      for (i=0; i<n; ++i) {
        g = groups[i];
        g.x += (dx[i] += x);
        g.y += (dy[i] += y);
        bounds.union(g.mark.bounds.union(g.bounds.translate(dx[i], dy[i])));
        if (dirty) view.dirty(g);
      }
  
      return bounds;
    }
  
    function trellisLayout(view, group, opt) {
      var views = gridLayoutGroups(group),
          groups = views.marks,
          bbox = opt.bounds === Flush ? boundFlush : boundFull,
          off = opt.offset,
          ncols = opt.columns || groups.length,
          nrows = ncols < 0 ? 1 : Math.ceil(groups.length / ncols),
          cells = nrows * ncols,
          x, y, x2, y2, anchor, band, offset;
  
      // -- initial grid layout
      const bounds = gridLayout(view, groups, opt);
  
      // -- layout grid headers and footers --
  
      // perform row header layout
      if (views.rowheaders) {
        band = get$2(opt.headerBand, Row, null);
        x = layoutHeaders(view, views.rowheaders, groups, ncols, nrows, -get$2(off, 'rowHeader'), min, 0, bbox, 'x1', 0, ncols, 1, band);
      }
  
      // perform column header layout
      if (views.colheaders) {
        band = get$2(opt.headerBand, Column, null);
        y = layoutHeaders(view, views.colheaders, groups, ncols, ncols, -get$2(off, 'columnHeader'), min, 1, bbox, 'y1', 0, 1, ncols, band);
      }
  
      // perform row footer layout
      if (views.rowfooters) {
        band = get$2(opt.footerBand, Row, null);
        x2 = layoutHeaders(view, views.rowfooters, groups, ncols, nrows,  get$2(off, 'rowFooter'), max, 0, bbox, 'x2', ncols-1, ncols, 1, band);
      }
  
      // perform column footer layout
      if (views.colfooters) {
        band = get$2(opt.footerBand, Column, null);
        y2 = layoutHeaders(view, views.colfooters, groups, ncols, ncols,  get$2(off, 'columnFooter'), max, 1, bbox, 'y2', cells-ncols, 1, ncols, band);
      }
  
      // perform row title layout
      if (views.rowtitle) {
        anchor = get$2(opt.titleAnchor, Row);
        offset = get$2(off, 'rowTitle');
        offset = anchor === End ? x2 + offset : x - offset;
        band = get$2(opt.titleBand, Row, 0.5);
        layoutTitle(view, views.rowtitle, offset, 0, bounds, band);
      }
  
      // perform column title layout
      if (views.coltitle) {
        anchor = get$2(opt.titleAnchor, Column);
        offset = get$2(off, 'columnTitle');
        offset = anchor === End ? y2 + offset : y - offset;
        band = get$2(opt.titleBand, Column, 0.5);
        layoutTitle(view, views.coltitle, offset, 1, bounds, band);
      }
    }
  
    function boundFlush(item, field) {
      return field === 'x1' ? (item.x || 0)
        : field === 'y1' ? (item.y || 0)
        : field === 'x2' ? (item.x || 0) + (item.width || 0)
        : field === 'y2' ? (item.y || 0) + (item.height || 0)
        : undefined;
    }
  
    function boundFull(item, field) {
      return item.bounds[field];
    }
  
    // aggregation functions for grid margin determination
    function min(a, b) { return Math.floor(Math.min(a, b)); }
    function max(a, b) { return Math.ceil(Math.max(a, b)); }
  
    function layoutHeaders(view, headers, groups, ncols, limit, offset, agg, isX, bound, bf, start, stride, back, band) {
      var n = groups.length,
          init = 0,
          edge = 0,
          i, j, k, m, b, h, g, x, y;
  
      // if no groups, early exit and return 0
      if (!n) return init;
  
      // compute margin
      for (i=start; i<n; i+=stride) {
        if (groups[i]) init = agg(init, bound(groups[i], bf));
      }
  
      // if no headers, return margin calculation
      if (!headers.length) return init;
  
      // check if number of headers exceeds number of rows or columns
      if (headers.length > limit) {
        view.warn('Grid headers exceed limit: ' + limit);
        headers = headers.slice(0, limit);
      }
  
      // apply offset
      init += offset;
  
      // clear mark bounds for all headers
      for (j=0, m=headers.length; j<m; ++j) {
        view.dirty(headers[j]);
        headers[j].mark.bounds.clear();
      }
  
      // layout each header
      for (i=start, j=0, m=headers.length; j<m; ++j, i+=stride) {
        h = headers[j];
        b = h.mark.bounds;
  
        // search for nearest group to align to
        // necessary if table has empty cells
        for (k=i; k >= 0 && (g = groups[k]) == null; k-=back);
  
        // assign coordinates and update bounds
        if (isX) {
          x = band == null ? g.x : Math.round(g.bounds.x1 + band * g.bounds.width());
          y = init;
        } else {
          x = init;
          y = band == null ? g.y : Math.round(g.bounds.y1 + band * g.bounds.height());
        }
        b.union(h.bounds.translate(x - (h.x || 0), y - (h.y || 0)));
        h.x = x;
        h.y = y;
        view.dirty(h);
  
        // update current edge of layout bounds
        edge = agg(edge, b[bf]);
      }
  
      return edge;
    }
  
    function layoutTitle(view, g, offset, isX, bounds, band) {
      if (!g) return;
      view.dirty(g);
  
      // compute title coordinates
      var x = offset, y = offset;
      isX
        ? (x = Math.round(bounds.x1 + band * bounds.width()))
        : (y = Math.round(bounds.y1 + band * bounds.height()));
  
      // assign coordinates and update bounds
      g.bounds.translate(x - (g.x || 0), y - (g.y || 0));
      g.mark.bounds.clear().union(g.bounds);
      g.x = x;
      g.y = y;
  
      // queue title for redraw
      view.dirty(g);
    }
  
    // utility for looking up legend layout configuration
    function lookup$2(config, orient) {
      const opt = config[orient] || {};
      return (key, d) => opt[key] != null ? opt[key]
        : config[key] != null ? config[key]
        : d;
    }
  
    // if legends specify offset directly, use the maximum specified value
    function offsets(legends, value) {
      var max = -Infinity;
      legends.forEach(item => {
        if (item.offset != null) max = Math.max(max, item.offset);
      });
      return max > -Infinity ? max : value;
    }
  
    function legendParams(g, orient, config, xb, yb, w, h) {
      const _ = lookup$2(config, orient),
            offset = offsets(g, _('offset', 0)),
            anchor = _('anchor', Start),
            mult = anchor === End ? 1 : anchor === Middle ? 0.5 : 0;
  
      const p = {
        align:   Each,
        bounds:  _('bounds', Flush),
        columns: _('direction') === 'vertical' ? 1 : g.length,
        padding: _('margin', 8),
        center:  _('center'),
        nodirty: true
      };
  
      switch (orient) {
        case Left:
          p.anchor = {
            x: Math.floor(xb.x1) - offset, column: End,
            y: mult * (h || xb.height() + 2 * xb.y1), row: anchor
          };
          break;
        case Right:
          p.anchor = {
            x: Math.ceil(xb.x2) + offset,
            y: mult * (h || xb.height() + 2 * xb.y1), row: anchor
          };
          break;
        case Top:
          p.anchor = {
            y: Math.floor(yb.y1) - offset, row: End,
            x: mult * (w || yb.width() + 2 * yb.x1), column: anchor
          };
          break;
        case Bottom:
          p.anchor = {
            y: Math.ceil(yb.y2) + offset,
            x: mult * (w || yb.width() + 2 * yb.x1), column: anchor
          };
          break;
        case TopLeft:
          p.anchor = {x: offset, y: offset};
          break;
        case TopRight:
          p.anchor = {x: w - offset, y: offset, column: End};
          break;
        case BottomLeft:
          p.anchor = {x: offset, y: h - offset, row: End};
          break;
        case BottomRight:
          p.anchor = {x: w - offset, y: h - offset, column: End, row: End};
          break;
      }
  
      return p;
    }
  
    function legendLayout(view, legend) {
      var item = legend.items[0],
          datum = item.datum,
          orient = item.orient,
          bounds = item.bounds,
          x = item.x, y = item.y, w, h;
  
      // cache current bounds for later comparison
      item._bounds
        ? item._bounds.clear().union(bounds)
        : item._bounds = bounds.clone();
      bounds.clear();
  
      // adjust legend to accommodate padding and title
      legendGroupLayout(view, item, item.items[0].items[0]);
  
      // aggregate bounds to determine size, and include origin
      bounds = legendBounds(item, bounds);
      w = 2 * item.padding;
      h = 2 * item.padding;
      if (!bounds.empty()) {
        w = Math.ceil(bounds.width() + w);
        h = Math.ceil(bounds.height() + h);
      }
  
      if (datum.type === Symbols) {
        legendEntryLayout(item.items[0].items[0].items[0].items);
      }
  
      if (orient !== None$1) {
        item.x = x = 0;
        item.y = y = 0;
      }
      item.width = w;
      item.height = h;
      boundStroke(bounds.set(x, y, x + w, y + h), item);
      item.mark.bounds.clear().union(bounds);
  
      return item;
    }
  
    function legendBounds(item, b) {
      // aggregate item bounds
      item.items.forEach(_ => b.union(_.bounds));
  
      // anchor to legend origin
      b.x1 = item.padding;
      b.y1 = item.padding;
  
      return b;
    }
  
    function legendGroupLayout(view, item, entry) {
      var pad = item.padding,
          ex = pad - entry.x,
          ey = pad - entry.y;
  
      if (!item.datum.title) {
        if (ex || ey) translate$2(view, entry, ex, ey);
      } else {
        var title = item.items[1].items[0],
            anchor = title.anchor,
            tpad = item.titlePadding || 0,
            tx = pad - title.x,
            ty = pad - title.y;
  
        switch (title.orient) {
          case Left:
            ex += Math.ceil(title.bounds.width()) + tpad;
            break;
          case Right:
          case Bottom:
            break;
          default:
            ey += title.fontSize + tpad;
        }
        if (ex || ey) translate$2(view, entry, ex, ey);
  
        switch (title.orient) {
          case Left:
            ty += legendTitleOffset(item, entry, title, anchor, 0, 1);
            break;
          case Right:
            tx += legendTitleOffset(item, entry, title, End, 1, 0) + tpad;
            ty += legendTitleOffset(item, entry, title, anchor, 0, 1);
            break;
          case Bottom:
            tx += legendTitleOffset(item, entry, title, anchor, 1, 0);
            ty += legendTitleOffset(item, entry, title, End, 0, 0, 1) + tpad;
            break;
          default:
            tx += legendTitleOffset(item, entry, title, anchor, 1, 0);
        }
        if (tx || ty) translate$2(view, title, tx, ty);
  
        // translate legend if title pushes into negative coordinates
        if ((tx = Math.round(title.bounds.x1 - pad)) < 0) {
          translate$2(view, entry, -tx, 0);
          translate$2(view, title, -tx, 0);
        }
      }
    }
  
    function legendTitleOffset(item, entry, title, anchor, x, lr, noBar) {
      const grad = item.datum.type !== 'symbol',
            vgrad = title.datum.vgrad,
            e = grad && (lr || !vgrad) && !noBar ? entry.items[0] : entry,
            s = e.bounds[x ? 'x2' : 'y2'] - item.padding,
            u = vgrad && lr ? s : 0,
            v = vgrad && lr ? 0 : s;
  
      return Math.round(anchor === Start ? u : anchor === End ? v : 0.5 * s);
    }
  
    function translate$2(view, item, dx, dy) {
      item.x += dx;
      item.y += dy;
      item.bounds.translate(dx, dy);
      item.mark.bounds.translate(dx, dy);
      view.dirty(item);
    }
  
    function legendEntryLayout(entries) {
      // get max widths for each column
      var widths = entries.reduce(function(w, g) {
        w[g.column] = Math.max(g.bounds.x2 - g.x, w[g.column] || 0);
        return w;
      }, {});
  
      // set dimensions of legend entry groups
      entries.forEach(function(g) {
        g.width  = widths[g.column];
        g.height = g.bounds.y2 - g.y;
      });
    }
  
    function titleLayout(view, title, width, height, viewBounds) {
      var item = title.items[0],
          frame = item.frame,
          orient = item.orient,
          anchor = item.anchor,
          offset = item.offset,
          bounds = item.bounds,
          vertical = (orient === Left || orient === Right),
          start = 0,
          end = vertical ? height : width,
          x = 0, y = 0, pos;
  
      if (frame !== Group) {
        orient === Left ? (start = viewBounds.y2, end = viewBounds.y1)
          : orient === Right ? (start = viewBounds.y1, end = viewBounds.y2)
          : (start = viewBounds.x1, end = viewBounds.x2);
      } else if (orient === Left) {
        start = height, end = 0;
      }
  
      pos = (anchor === Start) ? start
        : (anchor === End) ? end
        : (start + end) / 2;
  
      tempBounds$2.clear().union(bounds);
  
      // position title text
      switch (orient) {
        case Top:
          x = pos;
          y = viewBounds.y1 - offset;
          break;
        case Left:
          x = viewBounds.x1 - offset;
          y = pos;
          break;
        case Right:
          x = viewBounds.x2 + offset;
          y = pos;
          break;
        case Bottom:
          x = pos;
          y = viewBounds.y2 + offset;
          break;
        default:
          x = item.x;
          y = item.y;
      }
  
      bounds.translate(x - (item.x || 0), y - (item.y || 0));
      if (set(item, 'x', x) | set(item, 'y', y)) {
        item.bounds = tempBounds$2;
        view.dirty(item);
        item.bounds = bounds;
        view.dirty(item);
      }
  
      // update bounds
      return title.bounds.clear().union(bounds);
    }
  
    /**
     * Layout view elements such as axes and legends.
     * Also performs size adjustments.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {object} params.mark - Scenegraph mark of groups to layout.
     */
    function ViewLayout(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$S = inherits(ViewLayout, Transform);
  
    prototype$S.transform = function(_, pulse) {
      // TODO incremental update, output?
      var view = pulse.dataflow;
      _.mark.items.forEach(function(group) {
        if (_.layout) trellisLayout(view, group, _.layout);
        layoutGroup(view, group, _);
      });
      if (_.modified()) pulse.reflow();
      return pulse;
    };
  
    function layoutGroup(view, group, _) {
      var items = group.items,
          width = Math.max(0, group.width || 0),
          height = Math.max(0, group.height || 0),
          viewBounds = new Bounds().set(0, 0, width, height),
          xBounds = viewBounds.clone(),
          yBounds = viewBounds.clone(),
          legends = [], title,
          mark, orient, b, i, n;
  
      // layout axes, gather legends, collect bounds
      for (i=0, n=items.length; i<n; ++i) {
        mark = items[i];
        switch (mark.role) {
          case AxisRole:
            b = isYAxis(mark) ? xBounds : yBounds;
            b.union(axisLayout(view, mark, width, height));
            break;
          case TitleRole:
            title = mark;
            break;
          case LegendRole:
            legends.push(legendLayout(view, mark));
            break;
          case FrameRole:
          case ScopeRole:
          case RowHeader:
          case RowFooter:
          case RowTitle:
          case ColHeader:
          case ColFooter:
          case ColTitle:
            xBounds.union(mark.bounds);
            yBounds.union(mark.bounds);
            break;
          default:
            viewBounds.union(mark.bounds);
        }
      }
  
      // layout legends, adjust viewBounds
      if (legends.length) {
        // group legends by orient
        const l = {};
        legends.forEach(item => {
          orient = item.orient || Right;
          if (orient !== None$1) (l[orient] || (l[orient] = [])).push(item);
        });
  
        // perform grid layout for each orient group
        for (let orient in l) {
          const g = l[orient];
          gridLayout(view, g, legendParams(
            g, orient, _.legends, xBounds, yBounds, width, height
          ));
        }
  
        // update view bounds
        legends.forEach(item => {
          const b = item.bounds;
  
          if (!b.equals(item._bounds)) {
            item.bounds = item._bounds;
            view.dirty(item); // dirty previous location
            item.bounds = b;
            view.dirty(item);
          }
  
          if (_.autosize && _.autosize.type === Fit) {
            // For autosize fit, incorporate the orthogonal dimension only.
            // Legends that overrun the chart area will then be clipped;
            // otherwise the chart area gets reduced to nothing!
            switch(item.orient) {
              case Left:
              case Right:
                viewBounds.add(b.x1, 0).add(b.x2, 0);
                break;
              case Top:
              case Bottom:
                viewBounds.add(0, b.y1).add(0, b.y2);
            }
          } else {
            viewBounds.union(b);
          }
        });
      }
  
      // combine bounding boxes
      viewBounds.union(xBounds).union(yBounds);
  
      // layout title, adjust bounds
      if (title) {
        viewBounds.union(titleLayout(view, title, width, height, viewBounds));
      }
  
      // perform size adjustment
      viewSizeLayout(view, group, viewBounds, _);
    }
  
    function viewSizeLayout(view, group, viewBounds, _) {
      var auto = _.autosize || {},
          type = auto.type,
          viewWidth = view._width,
          viewHeight = view._height,
          padding = view.padding();
  
      if (view._autosize < 1 || !type) return;
  
      var width  = Math.max(0, group.width || 0),
          left   = Math.max(0, Math.ceil(-viewBounds.x1)),
          right  = Math.max(0, Math.ceil(viewBounds.x2 - width)),
          height = Math.max(0, group.height || 0),
          top    = Math.max(0, Math.ceil(-viewBounds.y1)),
          bottom = Math.max(0, Math.ceil(viewBounds.y2 - height));
  
      if (auto.contains === Padding) {
        viewWidth -= padding.left + padding.right;
        viewHeight -= padding.top + padding.bottom;
      }
  
      if (type === None$1) {
        left = 0;
        top = 0;
        width = viewWidth;
        height = viewHeight;
      }
  
      else if (type === Fit) {
        width = Math.max(0, viewWidth - left - right);
        height = Math.max(0, viewHeight - top - bottom);
      }
  
      else if (type === FitX) {
        width = Math.max(0, viewWidth - left - right);
        viewHeight = height + top + bottom;
      }
  
      else if (type === FitY) {
        viewWidth = width + left + right;
        height = Math.max(0, viewHeight - top - bottom);
      }
  
      else if (type === Pad) {
        viewWidth = width + left + right;
        viewHeight = height + top + bottom;
      }
  
      view._resizeView(
        viewWidth, viewHeight,
        width, height,
        [left, top],
        auto.resize
      );
    }
  
  
  
    var vtx = /*#__PURE__*/Object.freeze({
      bound: Bound,
      identifier: Identifier,
      mark: Mark,
      overlap: Overlap,
      render: Render,
      viewlayout: ViewLayout
    });
  
    function bandSpace(count, paddingInner, paddingOuter) {
      var space = count - paddingInner + paddingOuter * 2;
      return count ? (space > 0 ? space : 1) : 0;
    }
  
    const Identity = 'identity';
  
    const Linear = 'linear';
    const Log = 'log';
    const Pow = 'pow';
    const Sqrt = 'sqrt';
    const Symlog = 'symlog';
  
    const Time = 'time';
    const UTC = 'utc';
  
    const Sequential = 'sequential';
    const Diverging = 'diverging';
  
    const Quantile = 'quantile';
    const Quantize = 'quantize';
    const Threshold = 'threshold';
  
    const Ordinal = 'ordinal';
    const Point = 'point';
    const Band = 'band';
    const BinOrdinal = 'bin-ordinal';
  
    function isValidScaleType(type) {
      switch (type) {
        case Identity:
        case Linear:
        case Log:
        case Pow:
        case Sqrt:
        case Symlog:
        case Time:
        case UTC:
        case Sequential:
        case Quantile:
        case Quantize:
        case Threshold:
        case Ordinal:
        case Point:
        case Band:
        case BinOrdinal:
          return true;
      }
      return false;
    }
  
    function isQuantile(key) {
      return key === Quantile;
    }
  
    function isSequential(key) {
      return key && key.startsWith(Sequential);
    }
  
    function isDiverging(key) {
      return key && key.startsWith(Diverging);
    }
  
    function isInterpolating(key) {
      return isSequential(key) || isDiverging(key);
    }
  
    function isLogarithmic(key) {
      return key === Log || key.endsWith('-log');
    }
  
    function isContinuous(key) {
      switch (key) {
        case Linear:
        case Log:
        case Pow:
        case Sqrt:
        case Symlog:
        case Time:
        case UTC:
        case Sequential:
          return true;
      }
      return false;
    }
  
    function isDiscrete(key) {
      return key === BinOrdinal
        || key === Ordinal
        || key === Band
        || key === Point;
    }
  
    function isDiscretizing(key) {
      return key === BinOrdinal
        || key === Quantile
        || key === Quantize
        || key === Threshold;
    }
  
    var time = {
      millisecond: d3Time.timeMillisecond,
      second:      d3Time.timeSecond,
      minute:      d3Time.timeMinute,
      hour:        d3Time.timeHour,
      day:         d3Time.timeDay,
      week:        d3Time.timeWeek,
      month:       d3Time.timeMonth,
      year:        d3Time.timeYear
    };
  
    var utc = {
      millisecond: d3Time.utcMillisecond,
      second:      d3Time.utcSecond,
      minute:      d3Time.utcMinute,
      hour:        d3Time.utcHour,
      day:         d3Time.utcDay,
      week:        d3Time.utcWeek,
      month:       d3Time.utcMonth,
      year:        d3Time.utcYear
    };
  
    function timeInterval(unit, type) {
      const t = (type === UTC ? utc : time);
      return t.hasOwnProperty(unit) && t[unit];
    }
  
    function invertRange(scale) {
      return function(_) {
        var lo = _[0],
            hi = _[1],
            t;
  
        if (hi < lo) {
          t = lo;
          lo = hi;
          hi = t;
        }
  
        return [
          scale.invert(lo),
          scale.invert(hi)
        ];
      }
    }
  
    function invertRangeExtent(scale) {
      return function(_) {
        var range = scale.range(),
            lo = _[0],
            hi = _[1],
            min = -1, max, t, i, n;
  
        if (hi < lo) {
          t = lo;
          lo = hi;
          hi = t;
        }
  
        for (i=0, n=range.length; i<n; ++i) {
          if (range[i] >= lo && range[i] <= hi) {
            if (min < 0) min = i;
            max = i;
          }
        }
  
        if (min < 0) return undefined;
  
        lo = scale.invertExtent(range[min]);
        hi = scale.invertExtent(range[max]);
  
        return [
          lo[0] === undefined ? lo[1] : lo[0],
          hi[1] === undefined ? hi[0] : hi[1]
        ];
      }
    }
  
    function band() {
      var scale = $$1.scaleOrdinal().unknown(undefined),
          domain = scale.domain,
          ordinalRange = scale.range,
          range = [0, 1],
          step,
          bandwidth,
          round = false,
          paddingInner = 0,
          paddingOuter = 0,
          align = 0.5;
  
      delete scale.unknown;
  
      function rescale() {
        var n = domain().length,
            reverse = range[1] < range[0],
            start = range[reverse - 0],
            stop = range[1 - reverse],
            space = bandSpace(n, paddingInner, paddingOuter);
  
        step = (stop - start) / (space || 1);
        if (round) {
          step = Math.floor(step);
        }
        start += (stop - start - step * (n - paddingInner)) * align;
        bandwidth = step * (1 - paddingInner);
        if (round) {
          start = Math.round(start);
          bandwidth = Math.round(bandwidth);
        }
        var values = d3Array.range(n).map(function(i) { return start + step * i; });
        return ordinalRange(reverse ? values.reverse() : values);
      }
  
      scale.domain = function(_) {
        if (arguments.length) {
          domain(_);
          return rescale();
        } else {
          return domain();
        }
      };
  
      scale.range = function(_) {
        if (arguments.length) {
          range = [+_[0], +_[1]];
          return rescale();
        } else {
          return range.slice();
        }
      };
  
      scale.rangeRound = function(_) {
        range = [+_[0], +_[1]];
        round = true;
        return rescale();
      };
  
      scale.bandwidth = function() {
        return bandwidth;
      };
  
      scale.step = function() {
        return step;
      };
  
      scale.round = function(_) {
        if (arguments.length) {
          round = !!_;
          return rescale();
        } else {
          return round;
        }
      };
  
      scale.padding = function(_) {
        if (arguments.length) {
          paddingOuter = Math.max(0, Math.min(1, _));
          paddingInner = paddingOuter;
          return rescale();
        } else {
          return paddingInner;
        }
      };
  
      scale.paddingInner = function(_) {
        if (arguments.length) {
          paddingInner = Math.max(0, Math.min(1, _));
          return rescale();
        } else {
          return paddingInner;
        }
      };
  
      scale.paddingOuter = function(_) {
        if (arguments.length) {
          paddingOuter = Math.max(0, Math.min(1, _));
          return rescale();
        } else {
          return paddingOuter;
        }
      };
  
      scale.align = function(_) {
        if (arguments.length) {
          align = Math.max(0, Math.min(1, _));
          return rescale();
        } else {
          return align;
        }
      };
  
      scale.invertRange = function(_) {
        // bail if range has null or undefined values
        if (_[0] == null || _[1] == null) return;
  
        var lo = +_[0],
            hi = +_[1],
            reverse = range[1] < range[0],
            values = reverse ? ordinalRange().reverse() : ordinalRange(),
            n = values.length - 1, a, b, t;
  
        // bail if either range endpoint is invalid
        if (lo !== lo || hi !== hi) return;
  
        // order range inputs, bail if outside of scale range
        if (hi < lo) {
          t = lo;
          lo = hi;
          hi = t;
        }
        if (hi < values[0] || lo > range[1-reverse]) return;
  
        // binary search to index into scale range
        a = Math.max(0, d3Array.bisectRight(values, lo) - 1);
        b = lo===hi ? a : d3Array.bisectRight(values, hi) - 1;
  
        // increment index a if lo is within padding gap
        if (lo - values[a] > bandwidth + 1e-10) ++a;
  
        if (reverse) {
          // map + swap
          t = a;
          a = n - b;
          b = n - t;
        }
        return (a > b) ? undefined : domain().slice(a, b+1);
      };
  
      scale.invert = function(_) {
        var value = scale.invertRange([_, _]);
        return value ? value[0] : value;
      };
  
      scale.copy = function() {
        return band()
            .domain(domain())
            .range(range)
            .round(round)
            .paddingInner(paddingInner)
            .paddingOuter(paddingOuter)
            .align(align);
      };
  
      return rescale();
    }
  
    function pointish(scale) {
      var copy = scale.copy;
  
      scale.padding = scale.paddingOuter;
      delete scale.paddingInner;
  
      scale.copy = function() {
        return pointish(copy());
      };
  
      return scale;
    }
  
    function point$1() {
      return pointish(band().paddingInner(1));
    }
  
    var map = Array.prototype.map;
  
    function numbers$1(_) {
      return map.call(_, function(x) { return +x; });
    }
  
    var slice = Array.prototype.slice;
  
    function scaleBinOrdinal() {
      var domain = [],
          range = [];
  
      function scale(x) {
        return x == null || x !== x
          ? undefined
          : range[(d3Array.bisect(domain, x) - 1) % range.length];
      }
  
      scale.domain = function(_) {
        if (arguments.length) {
          domain = numbers$1(_);
          return scale;
        } else {
          return domain.slice();
        }
      };
  
      scale.range = function(_) {
        if (arguments.length) {
          range = slice.call(_);
          return scale;
        } else {
          return range.slice();
        }
      };
  
      scale.tickFormat = function(count, specifier) {
        return $$1.tickFormat(domain[0], peek(domain), count == null ? 10 : count, specifier);
      };
  
      scale.copy = function() {
        return scaleBinOrdinal().domain(scale.domain()).range(scale.range());
      };
  
      return scale;
    }
  
    /**
     * Augment scales with their type and needed inverse methods.
     */
    function create(type, constructor) {
      return function scale() {
        var s = constructor();
  
        if (!s.invertRange) {
          s.invertRange = s.invert ? invertRange(s)
            : s.invertExtent ? invertRangeExtent(s)
            : undefined;
        }
  
        s.type = type;
        return s;
      };
    }
  
    function scale$1(type, scale) {
      if (arguments.length > 1) {
        scales[type] = create(type, scale);
        return this;
      } else {
        return scales.hasOwnProperty(type) ? scales[type] : undefined;
      }
    }
  
    var scales = {
      // identity scale
      [Identity]:      $$1.scaleIdentity,
  
      // continuous scales
      [Linear]:        $$1.scaleLinear,
      [Log]:           $$1.scaleLog,
      [Pow]:           $$1.scalePow,
      [Sqrt]:          $$1.scaleSqrt,
      [Symlog]:        $$1.scaleSymlog,
      [Time]:          $$1.scaleTime,
      [UTC]:           $$1.scaleUtc,
  
      // sequential scales
      [Sequential]:             $$1.scaleSequential, // backwards compat
      [Sequential+'-'+Linear]:  $$1.scaleSequential,
      [Sequential+'-'+Log]:     $$1.scaleSequentialLog,
      [Sequential+'-'+Pow]:     $$1.scaleSequentialPow,
      [Sequential+'-'+Sqrt]:    $$1.scaleSequentialSqrt,
      [Sequential+'-'+Symlog]:  $$1.scaleSequentialSymlog,
  
      // diverging scales
      [Diverging+'-'+Linear]:   $$1.scaleDiverging,
      [Diverging+'-'+Log]:      $$1.scaleDivergingLog,
      [Diverging+'-'+Pow]:      $$1.scaleDivergingPow,
      [Diverging+'-'+Sqrt]:     $$1.scaleDivergingSqrt,
      [Diverging+'-'+Symlog]:   $$1.scaleDivergingSymlog,
  
      // discretizing scales
      [Quantile]:      $$1.scaleQuantile,
      [Quantize]:      $$1.scaleQuantize,
      [Threshold]:     $$1.scaleThreshold,
  
      // discrete scales
      [BinOrdinal]:    scaleBinOrdinal,
      [Ordinal]:       $$1.scaleOrdinal,
      [Band]:          band,
      [Point]:         point$1
    };
  
    for (var key$1 in scales) {
      scale$1(key$1, scales[key$1]);
    }
  
    const scaleProps = ['clamp', 'base', 'constant', 'exponent'];
  
    function interpolateRange(interpolator, range) {
      var start = range[0],
          span = peek(range) - start;
      return function(i) { return interpolator(start + i * span); };
    }
  
    function interpolateColors(colors, type, gamma) {
      return $$2.piecewise(interpolate(type || 'rgb', gamma), colors);
    }
  
    function quantizeInterpolator(interpolator, count) {
      var samples = new Array(count),
          n = count + 1;
      for (var i = 0; i < count;) samples[i] = interpolator(++i / n);
      return samples;
    }
  
    function scaleFraction(scale, min, max) {
      var delta = max - min, i, t, s;
  
      if (!delta || !isFinite(delta)) {
        return constant(0.5);
      } else {
        i = (t = scale.type).indexOf('-');
        t = i < 0 ? t : t.slice(i + 1);
        s = scale$1(t)().domain([min, max]).range([0, 1]);
        scaleProps.forEach(m => scale[m] ? s[m](scale[m]()) : 0);
        return s;
      }
    }
  
    function interpolate(type, gamma) {
      var interp = $$2[method(type)];
      return (gamma != null && interp && interp.gamma)
        ? interp.gamma(gamma)
        : interp;
    }
  
    function method(type) {
      return 'interpolate' + type.toLowerCase()
        .split('-')
        .map(function(s) { return s[0].toUpperCase() + s.slice(1); })
        .join('');
    }
  
    const continuous = {
      blues: 'cfe1f2bed8eca8cee58fc1de74b2d75ba3cf4592c63181bd206fb2125ca40a4a90',
      greens: 'd3eecdc0e6baabdda594d3917bc77d60ba6c46ab5e329a512089430e7735036429',
      greys: 'e2e2e2d4d4d4c4c4c4b1b1b19d9d9d8888887575756262624d4d4d3535351e1e1e',
      oranges: 'fdd8b3fdc998fdb87bfda55efc9244f87f2cf06b18e4580bd14904b93d029f3303',
      purples: 'e2e1efd4d4e8c4c5e0b4b3d6a3a0cc928ec3827cb97566ae684ea25c3696501f8c',
      reds: 'fdc9b4fcb49afc9e80fc8767fa7051f6573fec3f2fdc2a25c81b1db21218970b13',
  
      blueGreen: 'd5efedc1e8e0a7ddd18bd2be70c6a958ba9144ad77319c5d2089460e7736036429',
      bluePurple: 'ccddecbad0e4a8c2dd9ab0d4919cc98d85be8b6db28a55a6873c99822287730f71',
      greenBlue: 'd3eecec5e8c3b1e1bb9bd8bb82cec269c2ca51b2cd3c9fc7288abd1675b10b60a1',
      orangeRed: 'fddcaffdcf9bfdc18afdad77fb9562f67d53ee6545e24932d32d1ebf130da70403',
      purpleBlue: 'dbdaebc8cee4b1c3de97b7d87bacd15b9fc93a90c01e7fb70b70ab056199045281',
      purpleBlueGreen: 'dbd8eac8cee4b0c3de93b7d872acd1549fc83892bb1c88a3097f8702736b016353',
      purpleRed: 'dcc9e2d3b3d7ce9eccd186c0da6bb2e14da0e23189d91e6fc61159ab07498f023a',
      redPurple: 'fccfccfcbec0faa9b8f98faff571a5ec539ddb3695c41b8aa908808d0179700174',
      yellowGreen: 'e4f4acd1eca0b9e2949ed68880c97c62bb6e47aa5e3297502083440e723b036034',
      yellowOrangeBrown: 'feeaa1fedd84fecc63feb746fca031f68921eb7215db5e0bc54c05ab3d038f3204',
      yellowOrangeRed: 'fee087fed16ffebd59fea849fd903efc7335f9522bee3423de1b20ca0b22af0225',
  
      blueOrange: '134b852f78b35da2cb9dcae1d2e5eff2f0ebfce0bafbbf74e8932fc5690d994a07',
      brownBlueGreen: '704108a0651ac79548e3c78af3e6c6eef1eac9e9e48ed1c74da79e187a72025147',
      purpleGreen: '5b1667834792a67fb6c9aed3e6d6e8eff0efd9efd5aedda971bb75368e490e5e29',
      purpleOrange: '4114696647968f83b7b9b4d6dadbebf3eeeafce0bafbbf74e8932fc5690d994a07',
      redBlue: '8c0d25bf363adf745ef4ae91fbdbc9f2efeed2e5ef9dcae15da2cb2f78b3134b85',
      redGrey: '8c0d25bf363adf745ef4ae91fcdccbfaf4f1e2e2e2c0c0c0969696646464343434',
      yellowGreenBlue: 'eff9bddbf1b4bde5b594d5b969c5be45b4c22c9ec02182b82163aa23479c1c3185',
      redYellowBlue: 'a50026d4322cf16e43fcac64fedd90faf8c1dcf1ecabd6e875abd04a74b4313695',
      redYellowGreen: 'a50026d4322cf16e43fcac63fedd8df9f7aed7ee8ea4d86e64bc6122964f006837',
      pinkYellowGreen: '8e0152c0267edd72adf0b3d6faddedf5f3efe1f2cab6de8780bb474f9125276419',
      spectral: '9e0142d13c4bf0704afcac63fedd8dfbf8b0e0f3a1a9dda269bda94288b55e4fa2',
  
      viridis: '440154470e61481a6c482575472f7d443a834144873d4e8a39568c35608d31688e2d708e2a788e27818e23888e21918d1f988b1fa08822a8842ab07f35b77943bf7154c56866cc5d7ad1518fd744a5db36bcdf27d2e21be9e51afde725',
      magma: '0000040404130b0924150e3720114b2c11603b0f704a107957157e651a80721f817f24828c29819a2e80a8327db6377ac43c75d1426fde4968e95462f1605df76f5cfa7f5efc8f65fe9f6dfeaf78febf84fece91fddea0fcedaffcfdbf',
      inferno: '0000040403130c0826170c3b240c4f330a5f420a68500d6c5d126e6b176e781c6d86216b932667a12b62ae305cbb3755c73e4cd24644dd513ae65c30ed6925f3771af8850ffb9506fca50afcb519fac62df6d645f2e661f3f484fcffa4',
      plasma: '0d088723069033059742039d5002a25d01a66a00a87801a88405a7900da49c179ea72198b12a90ba3488c33d80cb4779d35171da5a69e16462e76e5bed7953f2834cf68f44fa9a3dfca636fdb32ffec029fcce25f9dc24f5ea27f0f921',
  
      rainbow: '6e40aa883eb1a43db3bf3cafd83fa4ee4395fe4b83ff576eff6659ff7847ff8c38f3a130e2b72fcfcc36bee044aff05b8ff4576ff65b52f6673af27828ea8d1ddfa319d0b81cbecb23abd82f96e03d82e14c6edb5a5dd0664dbf6e40aa',
      sinebow: 'ff4040fc582af47218e78d0bd5a703bfbf00a7d5038de70b72f41858fc2a40ff402afc5818f4720be78d03d5a700bfbf03a7d50b8de71872f42a58fc4040ff582afc7218f48d0be7a703d5bf00bfd503a7e70b8df41872fc2a58ff4040',
  
      browns: 'eedbbdecca96e9b97ae4a865dc9856d18954c7784cc0673fb85536ad44339f3632',
      tealBlues: 'bce4d89dd3d181c3cb65b3c245a2b9368fae347da0306a932c5985',
      teals: 'bbdfdfa2d4d58ac9c975bcbb61b0af4da5a43799982b8b8c1e7f7f127273006667',
      warmGreys: 'dcd4d0cec5c1c0b8b4b3aaa7a59c9998908c8b827f7e7673726866665c5a59504e',
  
      goldGreen: 'f4d166d5ca60b6c35c98bb597cb25760a6564b9c533f8f4f33834a257740146c36',
      goldOrange: 'f4d166f8be5cf8aa4cf5983bf3852aef701be2621fd65322c54923b142239e3a26',
      goldRed: 'f4d166f6be59f9aa51fc964ef6834bee734ae56249db5247cf4244c43141b71d3e',
  
      lightGreyRed: 'efe9e6e1dad7d5cbc8c8bdb9bbaea9cd967ddc7b43e15f19df4011dc000b',
      lightGreyTeal: 'e4eaead6dcddc8ced2b7c2c7a6b4bc64b0bf22a6c32295c11f85be1876bc',
      lightMulti: 'e0f1f2c4e9d0b0de9fd0e181f6e072f6c053f3993ef77440ef4a3c',
      lightOrange: 'f2e7daf7d5baf9c499fab184fa9c73f68967ef7860e8645bde515bd43d5b',
      lightTealBlue: 'e3e9e0c0dccf9aceca7abfc859afc0389fb9328dad2f7ca0276b95255988',
  
      darkBlue: '3232322d46681a5c930074af008cbf05a7ce25c0dd38daed50f3faffffff',
      darkGold: '3c3c3c584b37725e348c7631ae8b2bcfa424ecc31ef9de30fff184ffffff',
      darkGreen: '3a3a3a215748006f4d048942489e4276b340a6c63dd2d836ffeb2cffffaa',
      darkMulti: '3737371f5287197d8c29a86995ce3fffe800ffffff',
      darkRed: '3434347036339e3c38cc4037e75d1eec8620eeab29f0ce32ffeb2c'
    };
  
    const discrete = {
      category10: '1f77b4ff7f0e2ca02cd627289467bd8c564be377c27f7f7fbcbd2217becf',
      category20: '1f77b4aec7e8ff7f0effbb782ca02c98df8ad62728ff98969467bdc5b0d58c564bc49c94e377c2f7b6d27f7f7fc7c7c7bcbd22dbdb8d17becf9edae5',
      category20b: '393b795254a36b6ecf9c9ede6379398ca252b5cf6bcedb9c8c6d31bd9e39e7ba52e7cb94843c39ad494ad6616be7969c7b4173a55194ce6dbdde9ed6',
      category20c: '3182bd6baed69ecae1c6dbefe6550dfd8d3cfdae6bfdd0a231a35474c476a1d99bc7e9c0756bb19e9ac8bcbddcdadaeb636363969696bdbdbdd9d9d9',
      tableau10: '4c78a8f58518e4575672b7b254a24beeca3bb279a2ff9da69d755dbab0ac',
      tableau20: '4c78a89ecae9f58518ffbf7954a24b88d27ab79a20f2cf5b43989483bcb6e45756ff9d9879706ebab0acd67195fcbfd2b279a2d6a5c99e765fd8b5a5',
      accent: '7fc97fbeaed4fdc086ffff99386cb0f0027fbf5b17666666',
      dark2: '1b9e77d95f027570b3e7298a66a61ee6ab02a6761d666666',
      paired: 'a6cee31f78b4b2df8a33a02cfb9a99e31a1cfdbf6fff7f00cab2d66a3d9affff99b15928',
      pastel1: 'fbb4aeb3cde3ccebc5decbe4fed9a6ffffcce5d8bdfddaecf2f2f2',
      pastel2: 'b3e2cdfdcdaccbd5e8f4cae4e6f5c9fff2aef1e2cccccccc',
      set1: 'e41a1c377eb84daf4a984ea3ff7f00ffff33a65628f781bf999999',
      set2: '66c2a5fc8d628da0cbe78ac3a6d854ffd92fe5c494b3b3b3',
      set3: '8dd3c7ffffb3bebadafb807280b1d3fdb462b3de69fccde5d9d9d9bc80bdccebc5ffed6f'
    };
  
    function colors(palette) {
      var n = palette.length / 6 | 0, c = new Array(n), i = 0;
      while (i < n) c[i] = '#' + palette.slice(i * 6, ++i * 6);
      return c;
    }
  
    function apply(_, f) {
      for (let k in _) scheme(k, f(_[k]));
    }
  
    const schemes = {};
    apply(discrete, colors);
    apply(continuous, _ => interpolateColors(colors(_)));
  
    function scheme(name, scheme) {
      name = name && name.toLowerCase();
      if (arguments.length > 1) {
        schemes[name] = scheme;
        return this;
      } else {
        return schemes[name];
      }
    }
  
    /**
     * Determine the tick count or interval function.
     * @param {Scale} scale - The scale for which to generate tick values.
     * @param {*} count - The desired tick count or interval specifier.
     * @param {number} minStep - The desired minimum step between tick values.
     * @return {*} - The tick count or interval function.
     */
    function tickCount(scale, count, minStep) {
      var step;
  
      if (isNumber(count) && minStep != null) {
        count = Math.min(count, ~~(span(scale.domain()) / minStep) || 1);
      }
  
      if (isObject(count)) {
        step = count.step;
        count = count.interval;
      }
  
      if (isString(count)) {
        count = timeInterval(count, scale.type)
              || error('Only time and utc scales accept interval strings.');
        if (step) count = count.every(step);
      }
  
      return count;
    }
  
    /**
     * Filter a set of candidate tick values, ensuring that only tick values
     * that lie within the scale range are included.
     * @param {Scale} scale - The scale for which to generate tick values.
     * @param {Array<*>} ticks - The candidate tick values.
     * @param {*} count - The tick count or interval function.
     * @return {Array<*>} - The filtered tick values.
     */
    function validTicks(scale, ticks, count) {
      var range = scale.range(),
          lo = Math.floor(range[0]),
          hi = Math.ceil(peek(range));
  
      if (lo > hi) {
        range = hi;
        hi = lo;
        lo = range;
      }
  
      ticks = ticks.filter(function(v) {
        v = scale(v);
        return lo <= v && v <= hi;
      });
  
      if (count > 0 && ticks.length > 1) {
        var endpoints = [ticks[0], peek(ticks)];
        while (ticks.length > count && ticks.length >= 3) {
          ticks = ticks.filter(function(_, i) { return !(i % 2); });
        }
        if (ticks.length < 3) {
          ticks = endpoints;
        }
      }
  
      return ticks;
    }
  
    /**
     * Generate tick values for the given scale and approximate tick count or
     * interval value. If the scale has a 'ticks' method, it will be used to
     * generate the ticks, with the count argument passed as a parameter. If the
     * scale lacks a 'ticks' method, the full scale domain will be returned.
     * @param {Scale} scale - The scale for which to generate tick values.
     * @param {*} [count] - The approximate number of desired ticks.
     * @return {Array<*>} - The generated tick values.
     */
    function tickValues(scale, count) {
      return scale.bins ? validTicks(scale, binValues(scale.bins, count))
        : scale.ticks ? scale.ticks(count)
        : scale.domain();
    }
  
    /**
     * Generate tick values for an array of bin values.
     * @param {Array<*>} bins - An array of bin boundaries.
     * @param {Number} [count] - The approximate number of desired ticks.
     * @return {Array<*>} - The generated tick values.
     */
    function binValues(bins, count) {
      var n = bins.length,
          stride = ~~(n / (count || n));
  
      return stride < 2
        ? bins.slice()
        : bins.filter(function(x, i) { return !(i % stride); });
    }
  
    /**
     * Generate a label format function for a scale. If the scale has a
     * 'tickFormat' method, it will be used to generate the formatter, with the
     * count and specifier arguments passed as parameters. If the scale lacks a
     * 'tickFormat' method, the returned formatter performs simple string coercion.
     * If the input scale is a logarithmic scale and the format specifier does not
     * indicate a desired decimal precision, a special variable precision formatter
     * that automatically trims trailing zeroes will be generated.
     * @param {Scale} scale - The scale for which to generate the label formatter.
     * @param {*} [count] - The approximate number of desired ticks.
     * @param {string} [specifier] - The format specifier. Must be a legal d3
     *   specifier string (see https://github.com/d3/d3-format#formatSpecifier).
     * @return {function(*):string} - The generated label formatter.
     */
    function tickFormat(scale, count, specifier, formatType) {
      var format = scale.tickFormat ? scale.tickFormat(count, specifier)
        : specifier && formatType === Time ? d3TimeFormat.timeFormat(specifier)
        : specifier ? d3Format.format(specifier)
        : String;
  
      if (isLogarithmic(scale.type)) {
        var logfmt = variablePrecision(specifier);
        format = scale.bins ? logfmt : filter$1(format, logfmt);
      }
  
      return format;
    }
  
    function filter$1(sourceFormat, targetFormat) {
      return function(_) {
        return sourceFormat(_) ? targetFormat(_) : '';
      };
    }
  
    function variablePrecision(specifier) {
      var s = d3Format.formatSpecifier(specifier || ',');
  
      if (s.precision == null) {
        s.precision = 12;
        switch (s.type) {
          case '%': s.precision -= 2; break;
          case 'e': s.precision -= 1; break;
        }
        return trimZeroes(
          d3Format.format(s),          // number format
          d3Format.format('.1f')(1)[1] // decimal point character
        );
      } else {
        return d3Format.format(s);
      }
    }
  
    function trimZeroes(format, decimalChar) {
      return function(x) {
        var str = format(x),
            dec = str.indexOf(decimalChar),
            idx, end;
  
        if (dec < 0) return str;
  
        idx = rightmostDigit(str, dec);
        end = idx < str.length ? str.slice(idx) : '';
        while (--idx > dec) if (str[idx] !== '0') { ++idx; break; }
  
        return str.slice(0, idx) + end;
      };
    }
  
    function rightmostDigit(str, dec) {
      var i = str.lastIndexOf('e'), c;
      if (i > 0) return i;
      for (i=str.length; --i > dec;) {
        c = str.charCodeAt(i);
        if (c >= 48 && c <= 57) return i + 1; // is digit
      }
    }
  
    /**
     * Generates axis ticks for visualizing a spatial scale.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Scale} params.scale - The scale to generate ticks for.
     * @param {*} [params.count=10] - The approximate number of ticks, or
     *   desired tick interval, to use.
     * @param {Array<*>} [params.values] - The exact tick values to use.
     *   These must be legal domain values for the provided scale.
     *   If provided, the count argument is ignored.
     * @param {function(*):string} [params.formatSpecifier] - A format specifier
     *   to use in conjunction with scale.tickFormat. Legal values are
     *   any valid d3 4.0 format specifier.
     * @param {function(*):string} [params.format] - The format function to use.
     *   If provided, the formatSpecifier argument is ignored.
     */
    function AxisTicks(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$T = inherits(AxisTicks, Transform);
  
    prototype$T.transform = function(_, pulse) {
      if (this.value && !_.modified()) {
        return pulse.StopPropagation;
      }
  
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS),
          ticks = this.value,
          scale = _.scale,
          tally = _.count == null ? (_.values ? _.values.length : 10) : _.count,
          count = tickCount(scale, tally, _.minstep),
          format = _.format || tickFormat(scale, count, _.formatSpecifier, _.formatType),
          values = _.values ? validTicks(scale, _.values, count) : tickValues(scale, count);
  
      if (ticks) out.rem = ticks;
  
      ticks = values.map(function(value, i) {
        return ingest({
          index: i / (values.length - 1 || 1),
          value: value,
          label: format(value)
        });
      });
  
      if (_.extra && ticks.length) {
        // add an extra tick pegged to the initial domain value
        // this is used to generate axes with 'binned' domains
        ticks.push(ingest({
          index: -1,
          extra: {value: ticks[0].value},
          label: ''
        }));
      }
  
      out.source = ticks;
      out.add = ticks;
      this.value = ticks;
  
      return out;
    };
  
    /**
     * Joins a set of data elements against a set of visual items.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): object} [params.item] - An item generator function.
     * @param {function(object): *} [params.key] - The key field associating data and visual items.
     */
    function DataJoin(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$U = inherits(DataJoin, Transform);
  
    function defaultItemCreate() {
      return ingest({});
    }
  
    function isExit(t) {
      return t.exit;
    }
  
    prototype$U.transform = function(_, pulse) {
      var df = pulse.dataflow,
          out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS),
          item = _.item || defaultItemCreate,
          key = _.key || tupleid,
          map = this.value;
  
      // prevent transient (e.g., hover) requests from
      // cascading across marks derived from marks
      if (isArray(out.encode)) {
        out.encode = null;
      }
  
      if (map && (_.modified('key') || pulse.modified(key))) {
        error('DataJoin does not support modified key function or fields.');
      }
  
      if (!map) {
        pulse = pulse.addAll();
        this.value = map = fastmap().test(isExit);
        map.lookup = function(t) { return map.get(key(t)); };
      }
  
      pulse.visit(pulse.ADD, function(t) {
        var k = key(t),
            x = map.get(k);
  
        if (x) {
          if (x.exit) {
            map.empty--;
            out.add.push(x);
          } else {
            out.mod.push(x);
          }
        } else {
          map.set(k, (x = item(t)));
          out.add.push(x);
        }
  
        x.datum = t;
        x.exit = false;
      });
  
      pulse.visit(pulse.MOD, function(t) {
        var k = key(t),
            x = map.get(k);
  
        if (x) {
          x.datum = t;
          out.mod.push(x);
        }
      });
  
      pulse.visit(pulse.REM, function(t) {
        var k = key(t),
            x = map.get(k);
  
        if (t === x.datum && !x.exit) {
          out.rem.push(x);
          x.exit = true;
          ++map.empty;
        }
      });
  
      if (pulse.changed(pulse.ADD_MOD)) out.modifies('datum');
  
      if (_.clean && map.empty > df.cleanThreshold) df.runAfter(map.clean);
  
      return out;
    };
  
    /**
     * Invokes encoding functions for visual items.
     * @constructor
     * @param {object} params - The parameters to the encoding functions. This
     *   parameter object will be passed through to all invoked encoding functions.
     * @param {object} [params.mod=false] - Flag indicating if tuples in the input
     *   mod set that are unmodified by encoders should be included in the output.
     * @param {object} param.encoders - The encoding functions
     * @param {function(object, object): boolean} [param.encoders.update] - Update encoding set
     * @param {function(object, object): boolean} [param.encoders.enter] - Enter encoding set
     * @param {function(object, object): boolean} [param.encoders.exit] - Exit encoding set
     */
    function Encode(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$V = inherits(Encode, Transform);
  
    prototype$V.transform = function(_, pulse) {
      var out = pulse.fork(pulse.ADD_REM),
          fmod = _.mod || false,
          encoders = _.encoders,
          encode = pulse.encode;
  
      // if an array, the encode directive includes additional sets
      // that must be defined in order for the primary set to be invoked
      // e.g., only run the update set if the hover set is defined
      if (isArray(encode)) {
        if (out.changed() || encode.every(function(e) { return encoders[e]; })) {
          encode = encode[0];
          out.encode = null; // consume targeted encode directive
        } else {
          return pulse.StopPropagation;
        }
      }
  
      // marshall encoder functions
      var reenter = encode === 'enter',
          update = encoders.update || falsy,
          enter = encoders.enter || falsy,
          exit = encoders.exit || falsy,
          set = (encode && !reenter ? encoders[encode] : update) || falsy;
  
      if (pulse.changed(pulse.ADD)) {
        pulse.visit(pulse.ADD, function(t) { enter(t, _); update(t, _); });
        out.modifies(enter.output);
        out.modifies(update.output);
        if (set !== falsy && set !== update) {
          pulse.visit(pulse.ADD, function(t) { set(t, _); });
          out.modifies(set.output);
        }
      }
  
      if (pulse.changed(pulse.REM) && exit !== falsy) {
        pulse.visit(pulse.REM, function(t) { exit(t, _); });
        out.modifies(exit.output);
      }
  
      if (reenter || set !== falsy) {
        var flag = pulse.MOD | (_.modified() ? pulse.REFLOW : 0);
        if (reenter) {
          pulse.visit(flag, function(t) {
            var mod = enter(t, _) || fmod;
            if (set(t, _) || mod) out.mod.push(t);
          });
          if (out.mod.length) out.modifies(enter.output);
        } else {
          pulse.visit(flag, function(t) {
            if (set(t, _) || fmod) out.mod.push(t);
          });
        }
        if (out.mod.length) out.modifies(set.output);
      }
  
      return out.changed() ? out : pulse.StopPropagation;
    };
  
    var Symbols$1  = 'symbol';
    var Discrete = 'discrete';
    var Gradient$1 = 'gradient';
  
    const symbols$1 = {
      [Quantile]:  'quantiles',
      [Quantize]:  'thresholds',
      [Threshold]: 'domain'
    };
  
    const formats$1 = {
      [Quantile]:  'quantiles',
      [Quantize]:  'domain'
    };
  
    function labelValues(scale, count) {
      return scale.bins ? binValues$1(scale.bins)
        : symbols$1[scale.type] ? thresholdValues(scale[symbols$1[scale.type]]())
        : tickValues(scale, count);
    }
  
    function thresholdFormat(scale, specifier) {
      var _ = scale[formats$1[scale.type]](),
          n = _.length,
          d = n > 1 ? _[1] - _[0] : _[0], i;
  
      for (i=1; i<n; ++i) {
        d = Math.min(d, _[i] - _[i-1]);
      }
  
      // 3 ticks times 10 for increased resolution
      return $$1.tickFormat(0, d, 3 * 10, specifier);
    }
  
    function thresholdValues(thresholds) {
      const values = [-Infinity].concat(thresholds);
      values.max = +Infinity;
  
      return values;
    }
  
    function binValues$1(bins) {
      const values = bins.slice(0, -1);
      values.max = peek(bins);
  
      return values;
    }
  
    function isDiscreteRange(scale) {
      return symbols$1[scale.type] || scale.bins;
    }
  
    function labelFormat(scale, count, type, specifier, formatType) {
      const format = formats$1[scale.type] && formatType !== Time
        ? thresholdFormat(scale, specifier)
        : tickFormat(scale, count, specifier, formatType);
  
      return type === Symbols$1 && isDiscreteRange(scale) ? formatRange(format)
        : type === Discrete ? formatDiscrete(format)
        : formatPoint(format);
    }
  
    function formatRange(format) {
      return function(value, index, array) {
        var limit = array[index + 1] || array.max || +Infinity,
            lo = formatValue(value, format),
            hi = formatValue(limit, format);
        return lo && hi ? lo + '\u2013' + hi : hi ? '< ' + hi : '\u2265 ' + lo;
      };
    }
  
    function formatDiscrete(format) {
      return function(value, index) {
        return index ? format(value) : null;
      }
    }
  
    function formatPoint(format) {
      return function(value) {
        return format(value);
      };
    }
  
    function formatValue(value, format) {
      return isFinite(value) ? format(value) : null;
    }
  
    function labelFraction(scale) {
      var domain = scale.domain(),
          count = domain.length - 1,
          lo = +domain[0],
          hi = +peek(domain),
          span = hi - lo;
  
      if (scale.type === Threshold) {
        var adjust = count ? span / count : 0.1;
        lo -= adjust;
        hi += adjust;
        span = hi - lo;
      }
  
      return function(value) {
        return (value - lo) / span;
      };
    }
  
    /**
     * Generates legend entries for visualizing a scale.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Scale} params.scale - The scale to generate items for.
     * @param {*} [params.count=5] - The approximate number of items, or
     *   desired tick interval, to use.
     * @param {Array<*>} [params.values] - The exact tick values to use.
     *   These must be legal domain values for the provided scale.
     *   If provided, the count argument is ignored.
     * @param {string} [params.formatSpecifier] - A format specifier
     *   to use in conjunction with scale.tickFormat. Legal values are
     *   any valid D3 format specifier string.
     * @param {function(*):string} [params.format] - The format function to use.
     *   If provided, the formatSpecifier argument is ignored.
     */
    function LegendEntries(params) {
      Transform.call(this, [], params);
    }
  
    var prototype$W = inherits(LegendEntries, Transform);
  
    prototype$W.transform = function(_, pulse) {
      if (this.value != null && !_.modified()) {
        return pulse.StopPropagation;
      }
  
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS),
          items = this.value,
          type  = _.type || Symbols$1,
          scale = _.scale,
          count = tickCount(scale, _.count == null ? 5 : _.count, _.minstep),
          format = _.format || labelFormat(scale, count, type, _.formatSpecifier, _.formatType),
          values = _.values || labelValues(scale, count),
          domain, fraction, size, offset;
  
      if (items) out.rem = items;
  
      if (type === Symbols$1) {
        if (isFunction(size = _.size)) {
          // if first value maps to size zero, remove from list (vega#717)
          if (!_.values && scale(values[0]) === 0) {
            values = values.slice(1);
          }
          // compute size offset for legend entries
          offset = values.reduce(function(max, value) {
            return Math.max(max, size(value, _));
          }, 0);
        } else {
          size = constant(offset = size || 8);
        }
  
        items = values.map(function(value, index) {
          return ingest({
            index:  index,
            label:  format(value, index, values),
            value:  value,
            offset: offset,
            size:   size(value, _)
          });
        });
      }
  
      else if (type === Gradient$1) {
        domain = scale.domain(),
        fraction = scaleFraction(scale, domain[0], peek(domain));
  
        // if automatic label generation produces 2 or fewer values,
        // use the domain end points instead (fixes vega/vega#1364)
        if (values.length < 3 && !_.values && domain[0] !== peek(domain)) {
          values = [domain[0], peek(domain)];
        }
  
        items = values.map(function(value, index) {
          return ingest({
            index: index,
            label: format(value, index, values),
            value: value,
            perc:  fraction(value)
          });
        });
      }
  
      else {
        size = values.length - 1;
        fraction = labelFraction(scale);
  
        items = values.map(function(value, index) {
          return ingest({
            index: index,
            label: format(value, index, values),
            value: value,
            perc:  index ? fraction(value) : 0,
            perc2: index === size ? 1 : fraction(values[index+1])
          });
        });
      }
  
      out.source = items;
      out.add = items;
      this.value = items;
  
      return out;
    };
  
    var Paths = fastmap({
      'line': line$2,
      'line-radial': lineR,
      'arc': arc$2,
      'arc-radial': arcR,
      'curve': curve,
      'curve-radial': curveR,
      'orthogonal-horizontal': orthoX,
      'orthogonal-vertical': orthoY,
      'orthogonal-radial': orthoR,
      'diagonal-horizontal': diagonalX,
      'diagonal-vertical': diagonalY,
      'diagonal-radial': diagonalR
    });
  
    function sourceX(t) { return t.source.x; }
    function sourceY(t) { return t.source.y; }
    function targetX(t) { return t.target.x; }
    function targetY(t) { return t.target.y; }
  
     /**
      * Layout paths linking source and target elements.
      * @constructor
      * @param {object} params - The parameters for this operator.
      */
    function LinkPath(params) {
      Transform.call(this, {}, params);
    }
  
    LinkPath.Definition = {
      "type": "LinkPath",
      "metadata": {"modifies": true},
      "params": [
        { "name": "sourceX", "type": "field", "default": "source.x" },
        { "name": "sourceY", "type": "field", "default": "source.y" },
        { "name": "targetX", "type": "field", "default": "target.x" },
        { "name": "targetY", "type": "field", "default": "target.y" },
        { "name": "orient", "type": "enum", "default": "vertical",
          "values": ["horizontal", "vertical", "radial"] },
        { "name": "shape", "type": "enum", "default": "line",
          "values": ["line", "arc", "curve", "diagonal", "orthogonal"] },
        { "name": "require", "type": "signal" },
        { "name": "as", "type": "string", "default": "path" }
      ]
    };
  
    var prototype$X = inherits(LinkPath, Transform);
  
    prototype$X.transform = function(_, pulse) {
      var sx = _.sourceX || sourceX,
          sy = _.sourceY || sourceY,
          tx = _.targetX || targetX,
          ty = _.targetY || targetY,
          as = _.as || 'path',
          orient = _.orient || 'vertical',
          shape = _.shape || 'line',
          path = Paths.get(shape + '-' + orient) || Paths.get(shape);
  
      if (!path) {
        error('LinkPath unsupported type: ' + _.shape
          + (_.orient ? '-' + _.orient : ''));
      }
  
      pulse.visit(pulse.SOURCE, function(t) {
        t[as] = path(sx(t), sy(t), tx(t), ty(t));
      });
  
      return pulse.reflow(_.modified()).modifies(as);
    };
  
    // -- Link Path Generation Methods -----
  
    function line$2(sx, sy, tx, ty) {
      return 'M' + sx + ',' + sy +
             'L' + tx + ',' + ty;
    }
  
    function lineR(sa, sr, ta, tr) {
      return line$2(
        sr * Math.cos(sa), sr * Math.sin(sa),
        tr * Math.cos(ta), tr * Math.sin(ta)
      );
    }
  
    function arc$2(sx, sy, tx, ty) {
      var dx = tx - sx,
          dy = ty - sy,
          rr = Math.sqrt(dx * dx + dy * dy) / 2,
          ra = 180 * Math.atan2(dy, dx) / Math.PI;
      return 'M' + sx + ',' + sy +
             'A' + rr + ',' + rr +
             ' ' + ra + ' 0 1' +
             ' ' + tx + ',' + ty;
    }
  
    function arcR(sa, sr, ta, tr) {
      return arc$2(
        sr * Math.cos(sa), sr * Math.sin(sa),
        tr * Math.cos(ta), tr * Math.sin(ta)
      );
    }
  
    function curve(sx, sy, tx, ty) {
      var dx = tx - sx,
          dy = ty - sy,
          ix = 0.2 * (dx + dy),
          iy = 0.2 * (dy - dx);
      return 'M' + sx + ',' + sy +
             'C' + (sx+ix) + ',' + (sy+iy) +
             ' ' + (tx+iy) + ',' + (ty-ix) +
             ' ' + tx + ',' + ty;
    }
  
    function curveR(sa, sr, ta, tr) {
      return curve(
        sr * Math.cos(sa), sr * Math.sin(sa),
        tr * Math.cos(ta), tr * Math.sin(ta)
      );
    }
  
    function orthoX(sx, sy, tx, ty) {
      return 'M' + sx + ',' + sy +
             'V' + ty + 'H' + tx;
    }
  
    function orthoY(sx, sy, tx, ty) {
      return 'M' + sx + ',' + sy +
             'H' + tx + 'V' + ty;
    }
  
    function orthoR(sa, sr, ta, tr) {
      var sc = Math.cos(sa),
          ss = Math.sin(sa),
          tc = Math.cos(ta),
          ts = Math.sin(ta),
          sf = Math.abs(ta - sa) > Math.PI ? ta <= sa : ta > sa;
      return 'M' + (sr*sc) + ',' + (sr*ss) +
             'A' + sr + ',' + sr + ' 0 0,' + (sf?1:0) +
             ' ' + (sr*tc) + ',' + (sr*ts) +
             'L' + (tr*tc) + ',' + (tr*ts);
    }
  
    function diagonalX(sx, sy, tx, ty) {
      var m = (sx + tx) / 2;
      return 'M' + sx + ',' + sy +
             'C' + m  + ',' + sy +
             ' ' + m  + ',' + ty +
             ' ' + tx + ',' + ty;
    }
  
    function diagonalY(sx, sy, tx, ty) {
      var m = (sy + ty) / 2;
      return 'M' + sx + ',' + sy +
             'C' + sx + ',' + m +
             ' ' + tx + ',' + m +
             ' ' + tx + ',' + ty;
    }
  
    function diagonalR(sa, sr, ta, tr) {
      var sc = Math.cos(sa),
          ss = Math.sin(sa),
          tc = Math.cos(ta),
          ts = Math.sin(ta),
          mr = (sr + tr) / 2;
      return 'M' + (sr*sc) + ',' + (sr*ss) +
             'C' + (mr*sc) + ',' + (mr*ss) +
             ' ' + (mr*tc) + ',' + (mr*ts) +
             ' ' + (tr*tc) + ',' + (tr*ts);
    }
  
    /**
     * Pie and donut chart layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The value field to size pie segments.
     * @param {number} [params.startAngle=0] - The start angle (in radians) of the layout.
     * @param {number} [params.endAngle=2π] - The end angle (in radians) of the layout.
     * @param {boolean} [params.sort] - Boolean flag for sorting sectors by value.
     */
    function Pie(params) {
      Transform.call(this, null, params);
    }
  
    Pie.Definition = {
      "type": "Pie",
      "metadata": {"modifies": true},
      "params": [
        { "name": "field", "type": "field" },
        { "name": "startAngle", "type": "number", "default": 0 },
        { "name": "endAngle", "type": "number", "default": 6.283185307179586 },
        { "name": "sort", "type": "boolean", "default": false },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": ["startAngle", "endAngle"] }
      ]
    };
  
    var prototype$Y = inherits(Pie, Transform);
  
    prototype$Y.transform = function(_, pulse) {
      var as = _.as || ['startAngle', 'endAngle'],
          startAngle = as[0],
          endAngle = as[1],
          field = _.field || one,
          start = _.startAngle || 0,
          stop = _.endAngle != null ? _.endAngle : 2 * Math.PI,
          data = pulse.source,
          values = data.map(field),
          n = values.length,
          a = start,
          k = (stop - start) / d3Array.sum(values),
          index = d3Array.range(n),
          i, t, v;
  
      if (_.sort) {
        index.sort(function(a, b) {
          return values[a] - values[b];
        });
      }
  
      for (i=0; i<n; ++i) {
        v = values[index[i]];
        t = data[index[i]];
        t[startAngle] = a;
        t[endAngle] = (a += v * k);
      }
  
      this.value = values;
      return pulse.reflow(_.modified()).modifies(as);
    };
  
    var DEFAULT_COUNT = 5;
  
    function includeZero(scale) {
      const type = scale.type;
      return !scale.bins && (
        type === Linear || type === Pow || type === Sqrt
      );
    }
  
    function includePad(type) {
      return isContinuous(type) && type !== Sequential;
    }
  
    var SKIP$2 = toSet([
      'set', 'modified', 'clear', 'type', 'scheme', 'schemeExtent', 'schemeCount',
      'domain', 'domainMin', 'domainMid', 'domainMax',
      'domainRaw', 'domainImplicit', 'nice', 'zero', 'bins',
      'range', 'rangeStep', 'round', 'reverse', 'interpolate', 'interpolateGamma'
    ]);
  
    /**
     * Maintains a scale function mapping data values to visual channels.
     * @constructor
     * @param {object} params - The parameters for this operator.
     */
    function Scale(params) {
      Transform.call(this, null, params);
      this.modified(true); // always treat as modified
    }
  
    var prototype$Z = inherits(Scale, Transform);
  
    prototype$Z.transform = function(_, pulse) {
      var df = pulse.dataflow,
          scale = this.value,
          key = scaleKey(_);
  
      if (!scale || key !== scale.type) {
        this.value = scale = scale$1(key)();
      }
  
      for (key in _) if (!SKIP$2[key]) {
        // padding is a scale property for band/point but not others
        if (key === 'padding' && includePad(scale.type)) continue;
        // invoke scale property setter, raise warning if not found
        isFunction(scale[key])
          ? scale[key](_[key])
          : df.warn('Unsupported scale property: ' + key);
      }
  
      configureRange(scale, _,
        configureBins(scale, _, configureDomain(scale, _, df))
      );
  
      return pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);
    };
  
    function scaleKey(_) {
      var t = _.type, d = '', n;
  
      // backwards compatibility pre Vega 5.
      if (t === Sequential) return Sequential + '-' + Linear;
  
      if (isContinuousColor(_)) {
        n = _.rawDomain ? _.rawDomain.length
          : _.domain ? _.domain.length + +(_.domainMid != null)
          : 0;
        d = n === 2 ? Sequential + '-'
          : n === 3 ? Diverging + '-'
          : '';
      }
  
      return ((d + t) || Linear).toLowerCase();
    }
  
    function isContinuousColor(_) {
      const t = _.type;
      return isContinuous(t) && t !== Time && t !== UTC && (
        _.scheme || _.range && _.range.length && _.range.every(isString)
      );
    }
  
    function configureDomain(scale, _, df) {
      // check raw domain, if provided use that and exit early
      var raw = rawDomain(scale, _.domainRaw, df);
      if (raw > -1) return raw;
  
      var domain = _.domain,
          type = scale.type,
          zero = _.zero || (_.zero === undefined && includeZero(scale)),
          n, mid;
  
      if (!domain) return 0;
  
      // adjust continuous domain for minimum pixel padding
      if (includePad(type) && _.padding && domain[0] !== peek(domain)) {
        domain = padDomain(type, domain, _.range, _.padding, _.exponent, _.constant);
      }
  
      // adjust domain based on zero, min, max settings
      if (zero || _.domainMin != null || _.domainMax != null || _.domainMid != null) {
        n = ((domain = domain.slice()).length - 1) || 1;
        if (zero) {
          if (domain[0] > 0) domain[0] = 0;
          if (domain[n] < 0) domain[n] = 0;
        }
        if (_.domainMin != null) domain[0] = _.domainMin;
        if (_.domainMax != null) domain[n] = _.domainMax;
  
        if (_.domainMid != null) {
          mid = _.domainMid;
          if (mid < domain[0] || mid > domain[n]) {
            df.warn('Scale domainMid exceeds domain min or max.', mid);
          }
          domain.splice(n, 0, mid);
        }
      }
  
      // set the scale domain
      scale.domain(domainCheck(type, domain, df));
  
      // if ordinal scale domain is defined, prevent implicit
      // domain construction as side-effect of scale lookup
      if (type === Ordinal) {
        scale.unknown(_.domainImplicit ? $$1.scaleImplicit : undefined);
      }
  
      // perform 'nice' adjustment as requested
      if (_.nice && scale.nice) {
        scale.nice((_.nice !== true && tickCount(scale, _.nice)) || null);
      }
  
      // return the cardinality of the domain
      return domain.length;
    }
  
    function rawDomain(scale, raw, df) {
      if (raw) {
        scale.domain(domainCheck(scale.type, raw, df));
        return raw.length;
      } else {
        return -1;
      }
    }
  
    function padDomain(type, domain, range, pad, exponent, constant) {
      var span = Math.abs(peek(range) - range[0]),
          frac = span / (span - 2 * pad),
          d = type === Log    ? zoomLog(domain, null, frac)
            : type === Sqrt   ? zoomPow(domain, null, frac, 0.5)
            : type === Pow    ? zoomPow(domain, null, frac, exponent || 1)
            : type === Symlog ? zoomSymlog(domain, null, frac, constant || 1)
            : zoomLinear(domain, null, frac);
  
      domain = domain.slice();
      domain[0] = d[0];
      domain[domain.length-1] = d[1];
      return domain;
    }
  
    function domainCheck(type, domain, df) {
      if (isLogarithmic(type)) {
        // sum signs of domain values
        // if all pos or all neg, abs(sum) === domain.length
        var s = Math.abs(domain.reduce(function(s, v) {
          return s + (v < 0 ? -1 : v > 0 ? 1 : 0);
        }, 0));
  
        if (s !== domain.length) {
          df.warn('Log scale domain includes zero: ' + $(domain));
        }
      }
      return domain;
    }
  
    function configureBins(scale, _, count) {
      let bins = _.bins;
  
      if (bins && !isArray(bins)) {
        // generate bin boundary array
        const domain = (bins.start == null || bins.stop == null) && scale.domain(),
              start = bins.start == null ? domain[0] : bins.start,
              stop = bins.stop == null ? peek(domain) : bins.stop,
              step = bins.step;
  
        if (!step) error('Scale bins parameter missing step property.');
        bins = d3Array.range(start, stop + step, step);
      }
  
      if (bins) {
        // assign bin boundaries to scale instance
        scale.bins = bins;
      } else if (scale.bins) {
        // no current bins, remove bins if previously set
        delete scale.bins;
      }
  
      // special handling for bin-ordinal scales
      if (scale.type === BinOrdinal) {
        if (!bins) {
          // the domain specifies the bins
          scale.bins = scale.domain();
        } else if (!_.domain && !_.domainRaw) {
          // the bins specify the domain
          scale.domain(bins);
          count = bins.length;
        }
      }
  
      // return domain cardinality
      return count;
    }
  
    function configureRange(scale, _, count) {
      var round = _.round || false,
          range = _.range;
  
      // if range step specified, calculate full range extent
      if (_.rangeStep != null) {
        range = configureRangeStep(scale.type, _, count);
      }
  
      // else if a range scheme is defined, use that
      else if (_.scheme) {
        range = configureScheme(scale.type, _, count);
        if (isFunction(range)) return scale.interpolator(range);
      }
  
      // given a range array for an interpolating scale, convert to interpolator
      else if (range && isInterpolating(scale.type)) {
        return scale.interpolator(
          interpolateColors(flip(range, _.reverse), _.interpolate, _.interpolateGamma)
        );
      }
  
      // configure rounding / interpolation
      if (range && _.interpolate && scale.interpolate) {
        scale.interpolate(interpolate(_.interpolate, _.interpolateGamma));
      } else if (isFunction(scale.round)) {
        scale.round(round);
      } else if (isFunction(scale.rangeRound)) {
        scale.interpolate(round ? $$2.interpolateRound : $$2.interpolate);
      }
  
      if (range) scale.range(flip(range, _.reverse));
    }
  
    function configureRangeStep(type, _, count) {
      if (type !== Band && type !== Point) {
        error('Only band and point scales support rangeStep.');
      }
  
      // calculate full range based on requested step size and padding
      var outer = (_.paddingOuter != null ? _.paddingOuter : _.padding) || 0,
          inner = type === Point ? 1
                : ((_.paddingInner != null ? _.paddingInner : _.padding) || 0);
      return [0, _.rangeStep * bandSpace(count, inner, outer)];
    }
  
    function configureScheme(type, _, count) {
      var extent = _.schemeExtent,
          name, scheme$1;
  
      if (isArray(_.scheme)) {
        scheme$1 = interpolateColors(_.scheme, _.interpolate, _.interpolateGamma);
      } else {
        name = _.scheme.toLowerCase();
        scheme$1 = scheme(name);
        if (!scheme$1) error('Unrecognized scheme name: ' + _.scheme);
      }
  
      // determine size for potential discrete range
      count = (type === Threshold) ? count + 1
        : (type === BinOrdinal) ? count - 1
        : (type === Quantile || type === Quantize) ? (+_.schemeCount || DEFAULT_COUNT)
        : count;
  
      // adjust and/or quantize scheme as appropriate
      return isInterpolating(type) ? adjustScheme(scheme$1, extent, _.reverse)
        : isFunction(scheme$1) ? quantizeInterpolator(adjustScheme(scheme$1, extent), count)
        : type === Ordinal ? scheme$1 : scheme$1.slice(0, count);
    }
  
    function adjustScheme(scheme, extent, reverse) {
      return (isFunction(scheme) && (extent || reverse))
        ? interpolateRange(scheme, flip(extent || [0, 1], reverse))
        : scheme;
    }
  
    function flip(array, reverse) {
      return reverse ? array.slice().reverse() : array;
    }
  
    /**
     * Sorts scenegraph items in the pulse source array.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(*,*): number} [params.sort] - A comparator
     *   function for sorting tuples.
     */
    function SortItems(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$_ = inherits(SortItems, Transform);
  
    prototype$_.transform = function(_, pulse) {
      var mod = _.modified('sort')
             || pulse.changed(pulse.ADD)
             || pulse.modified(_.sort.fields)
             || pulse.modified('datum');
  
      if (mod) pulse.source.sort(_.sort);
  
      this.modified(mod);
      return pulse;
    };
  
    var Zero = 'zero',
        Center = 'center',
        Normalize = 'normalize',
        DefOutput = ['y0', 'y1'];
  
    /**
     * Stack layout for visualization elements.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The value field to stack.
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors to groupby.
     * @param {function(object,object): number} [params.sort] - A comparator for stack sorting.
     * @param {string} [offset='zero'] - One of 'zero', 'center', 'normalize'.
     */
    function Stack(params) {
      Transform.call(this, null, params);
    }
  
    Stack.Definition = {
      "type": "Stack",
      "metadata": {"modifies": true},
      "params": [
        { "name": "field", "type": "field" },
        { "name": "groupby", "type": "field", "array": true },
        { "name": "sort", "type": "compare" },
        { "name": "offset", "type": "enum", "default": Zero, "values": [Zero, Center, Normalize] },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": DefOutput }
      ]
    };
  
    var prototype$$ = inherits(Stack, Transform);
  
    prototype$$.transform = function(_, pulse) {
      var as = _.as || DefOutput,
          y0 = as[0],
          y1 = as[1],
          field = _.field || one,
          stack = _.offset === Center ? stackCenter
                : _.offset === Normalize ? stackNormalize
                : stackZero,
          groups, i, n, max;
  
      // partition, sum, and sort the stack groups
      groups = partition$2(pulse.source, _.groupby, _.sort, field);
  
      // compute stack layouts per group
      for (i=0, n=groups.length, max=groups.max; i<n; ++i) {
        stack(groups[i], max, field, y0, y1);
      }
  
      return pulse.reflow(_.modified()).modifies(as);
    };
  
    function stackCenter(group, max, field, y0, y1) {
      var last = (max - group.sum) / 2,
          m = group.length,
          j = 0, t;
  
      for (; j<m; ++j) {
        t = group[j];
        t[y0] = last;
        t[y1] = (last += Math.abs(field(t)));
      }
    }
  
    function stackNormalize(group, max, field, y0, y1) {
      var scale = 1 / group.sum,
          last = 0,
          m = group.length,
          j = 0, v = 0, t;
  
      for (; j<m; ++j) {
        t = group[j];
        t[y0] = last;
        t[y1] = last = scale * (v += Math.abs(field(t)));
      }
    }
  
    function stackZero(group, max, field, y0, y1) {
      var lastPos = 0,
          lastNeg = 0,
          m = group.length,
          j = 0, v, t;
  
      for (; j<m; ++j) {
        t = group[j];
        v = +field(t);
        if (v < 0) {
          t[y0] = lastNeg;
          t[y1] = (lastNeg += v);
        } else {
          t[y0] = lastPos;
          t[y1] = (lastPos += v);
        }
      }
    }
  
    function partition$2(data, groupby, sort, field) {
      var groups = [],
          get = function(f) { return f(t); },
          map, i, n, m, t, k, g, s, max;
  
      // partition data points into stack groups
      if (groupby == null) {
        groups.push(data.slice());
      } else {
        for (map={}, i=0, n=data.length; i<n; ++i) {
          t = data[i];
          k = groupby.map(get);
          g = map[k];
          if (!g) {
            map[k] = (g = []);
            groups.push(g);
          }
          g.push(t);
        }
      }
  
      // compute sums of groups, sort groups as needed
      for (k=0, max=0, m=groups.length; k<m; ++k) {
        g = groups[k];
        for (i=0, s=0, n=g.length; i<n; ++i) {
          s += Math.abs(field(g[i]));
        }
        g.sum = s;
        if (s > max) max = s;
        if (sort) g.sort(sort);
      }
      groups.max = max;
  
      return groups;
    }
  
  
  
    var encode = /*#__PURE__*/Object.freeze({
      axisticks: AxisTicks,
      datajoin: DataJoin,
      encode: Encode,
      legendentries: LegendEntries,
      linkpath: LinkPath,
      pie: Pie,
      scale: Scale,
      sortitems: SortItems,
      stack: Stack,
      validTicks: validTicks
    });
  
    var CONTOUR_PARAMS = ['size', 'smooth'];
    var DENSITY_PARAMS = ['x', 'y', 'weight', 'size', 'cellSize', 'bandwidth'];
  
    /**
     * Generate contours based on kernel-density estimation of point data.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<number>} params.size - The dimensions [width, height] over which to compute contours.
     *  If the values parameter is provided, this must be the dimensions of the input data.
     *  If density estimation is performed, this is the output view dimensions in pixels.
     * @param {Array<number>} [params.values] - An array of numeric values representing an
     *  width x height grid of values over which to compute contours. If unspecified, this
     *  transform will instead attempt to compute contours for the kernel density estimate
     *  using values drawn from data tuples in the input pulse.
     * @param {function(object): number} [params.x] - The pixel x-coordinate accessor for density estimation.
     * @param {function(object): number} [params.y] - The pixel y-coordinate accessor for density estimation.
     * @param {function(object): number} [params.weight] - The data point weight accessor for density estimation.
     * @param {number} [params.cellSize] - Contour density calculation cell size.
     * @param {number} [params.bandwidth] - Kernel density estimation bandwidth.
     * @param {Array<number>} [params.thresholds] - Contour threshold array. If
     *   this parameter is set, the count and nice parameters will be ignored.
     * @param {number} [params.count] - The desired number of contours.
     * @param {boolean} [params.nice] - Boolean flag indicating if the contour
     *   threshold values should be automatically aligned to "nice"
     *   human-friendly values. Setting this flag may cause the number of
     *   thresholds to deviate from the specified count.
     * @param {boolean} [params.smooth] - Boolean flag indicating if the contour
     *   polygons should be smoothed using linear interpolation. The default is
     *   true. The parameter is ignored when using density estimation.
     */
    function Contour(params) {
      Transform.call(this, null, params);
    }
  
    Contour.Definition = {
      "type": "Contour",
      "metadata": {"generates": true},
      "params": [
        { "name": "size", "type": "number", "array": true, "length": 2, "required": true },
        { "name": "values", "type": "number", "array": true },
        { "name": "x", "type": "field" },
        { "name": "y", "type": "field" },
        { "name": "weight", "type": "field" },
        { "name": "cellSize", "type": "number" },
        { "name": "bandwidth", "type": "number" },
        { "name": "count", "type": "number" },
        { "name": "smooth", "type": "boolean" },
        { "name": "nice", "type": "boolean", "default": false },
        { "name": "thresholds", "type": "number", "array": true }
      ]
    };
  
    var prototype$10 = inherits(Contour, Transform);
  
    prototype$10.transform = function(_, pulse) {
      if (this.value && !pulse.changed() && !_.modified())
        return pulse.StopPropagation;
  
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS),
          count = _.count || 10,
          contour, params, values;
  
      if (_.values) {
        contour = d3Contour.contours();
        params = CONTOUR_PARAMS;
        values = _.values;
      } else {
        contour = d3Contour.contourDensity();
        params = DENSITY_PARAMS;
        values = pulse.materialize(pulse.SOURCE).source;
      }
  
      // set threshold parameter
      contour.thresholds(_.thresholds || (_.nice ? count : quantize(count)));
  
      // set all other parameters
      params.forEach(function(param) {
        if (_[param] != null) contour[param](_[param]);
      });
  
      if (this.value) out.rem = this.value;
      values = values && values.length ? contour(values).map(ingest) : [];
      this.value = out.source = out.add = values;
  
      return out;
    };
  
    function quantize(k) {
      return function(values) {
        var ex = d3Array.extent(values), x0 = ex[0], dx = ex[1] - x0,
            t = [], i = 1;
        for (; i<=k; ++i) t.push(x0 + dx * i / (k + 1));
        return t;
      };
    }
  
    var Feature = 'Feature';
    var FeatureCollection = 'FeatureCollection';
    var MultiPoint = 'MultiPoint';
  
    /**
     * Consolidate an array of [longitude, latitude] points or GeoJSON features
     * into a combined GeoJSON object. This transform is particularly useful for
     * combining geo data for a Projection's fit argument. The resulting GeoJSON
     * data is available as this transform's value. Input pulses are unchanged.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<function(object): *>} [params.fields] - A two-element array
     *   of field accessors for the longitude and latitude values.
     * @param {function(object): *} params.geojson - A field accessor for
     *   retrieving GeoJSON feature data.
     */
    function GeoJSON(params) {
      Transform.call(this, null, params);
    }
  
    GeoJSON.Definition = {
      "type": "GeoJSON",
      "metadata": {},
      "params": [
        { "name": "fields", "type": "field", "array": true, "length": 2 },
        { "name": "geojson", "type": "field" },
      ]
    };
  
    var prototype$11 = inherits(GeoJSON, Transform);
  
    prototype$11.transform = function(_, pulse) {
      var features = this._features,
          points = this._points,
          fields = _.fields,
          lon = fields && fields[0],
          lat = fields && fields[1],
          geojson = _.geojson,
          flag = pulse.ADD,
          mod;
  
      mod = _.modified()
        || pulse.changed(pulse.REM)
        || pulse.modified(accessorFields(geojson))
        || (lon && (pulse.modified(accessorFields(lon))))
        || (lat && (pulse.modified(accessorFields(lat))));
  
      if (!this.value || mod) {
        flag = pulse.SOURCE;
        this._features = (features = []);
        this._points = (points = []);
      }
  
      if (geojson) {
        pulse.visit(flag, function(t) {
          features.push(geojson(t));
        });
      }
  
      if (lon && lat) {
        pulse.visit(flag, function(t) {
          var x = lon(t),
              y = lat(t);
          if (x != null && y != null && (x = +x) === x && (y = +y) === y) {
            points.push([x, y]);
          }
        });
        features = features.concat({
          type: Feature,
          geometry: {
            type: MultiPoint,
            coordinates: points
          }
        });
      }
  
      this.value = {
        type: FeatureCollection,
        features: features
      };
    };
  
    var defaultPath = d3Geo.geoPath();
  
    var projectionProperties = [
      // standard properties in d3-geo
      'clipAngle',
      'clipExtent',
      'scale',
      'translate',
      'center',
      'rotate',
      'parallels',
      'precision',
      'reflectX',
      'reflectY',
  
      // extended properties in d3-geo-projections
      'coefficient',
      'distance',
      'fraction',
      'lobes',
      'parallel',
      'radius',
      'ratio',
      'spacing',
      'tilt'
    ];
  
    /**
     * Augment projections with their type and a copy method.
     */
    function create$1(type, constructor) {
      return function projection() {
        var p = constructor();
  
        p.type = type;
  
        p.path = d3Geo.geoPath().projection(p);
  
        p.copy = p.copy || function() {
          var c = projection();
          projectionProperties.forEach(function(prop) {
            if (p.hasOwnProperty(prop)) c[prop](p[prop]());
          });
          c.path.pointRadius(p.path.pointRadius());
          return c;
        };
  
        return p;
      };
    }
  
    function projection(type, proj) {
      if (!type || typeof type !== 'string') {
        throw new Error('Projection type must be a name string.');
      }
      type = type.toLowerCase();
      if (arguments.length > 1) {
        projections[type] = create$1(type, proj);
        return this;
      } else {
        return projections.hasOwnProperty(type) ? projections[type] : null;
      }
    }
  
    function getProjectionPath(proj) {
      return (proj && proj.path) || defaultPath;
    }
  
    var projections = {
      // base d3-geo projection types
      albers:               d3Geo.geoAlbers,
      albersusa:            d3Geo.geoAlbersUsa,
      azimuthalequalarea:   d3Geo.geoAzimuthalEqualArea,
      azimuthalequidistant: d3Geo.geoAzimuthalEquidistant,
      conicconformal:       d3Geo.geoConicConformal,
      conicequalarea:       d3Geo.geoConicEqualArea,
      conicequidistant:     d3Geo.geoConicEquidistant,
      equirectangular:      d3Geo.geoEquirectangular,
      gnomonic:             d3Geo.geoGnomonic,
      identity:             d3Geo.geoIdentity,
      mercator:             d3Geo.geoMercator,
      naturalEarth1:        d3Geo.geoNaturalEarth1,
      orthographic:         d3Geo.geoOrthographic,
      stereographic:        d3Geo.geoStereographic,
      transversemercator:   d3Geo.geoTransverseMercator
    };
  
    for (var key$2 in projections) {
      projection(key$2, projections[key$2]);
    }
  
    /**
     * Map GeoJSON data to an SVG path string.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(number, number): *} params.projection - The cartographic
     *   projection to apply.
     * @param {function(object): *} [params.field] - The field with GeoJSON data,
     *   or null if the tuple itself is a GeoJSON feature.
     * @param {string} [params.as='path'] - The output field in which to store
     *   the generated path data (default 'path').
     */
    function GeoPath(params) {
      Transform.call(this, null, params);
    }
  
    GeoPath.Definition = {
      "type": "GeoPath",
      "metadata": {"modifies": true},
      "params": [
        { "name": "projection", "type": "projection" },
        { "name": "field", "type": "field" },
        { "name": "pointRadius", "type": "number", "expr": true },
        { "name": "as", "type": "string", "default": "path" }
      ]
    };
  
    var prototype$12 = inherits(GeoPath, Transform);
  
    prototype$12.transform = function(_, pulse) {
      var out = pulse.fork(pulse.ALL),
          path = this.value,
          field = _.field || identity,
          as = _.as || 'path',
          flag = out.SOURCE;
  
      function set(t) { t[as] = path(field(t)); }
  
      if (!path || _.modified()) {
        // parameters updated, reset and reflow
        this.value = path = getProjectionPath(_.projection);
        out.materialize().reflow();
      } else {
        flag = field === identity || pulse.modified(field.fields)
          ? out.ADD_MOD
          : out.ADD;
      }
  
      var prev = initPath(path, _.pointRadius);
      out.visit(flag, set);
      path.pointRadius(prev);
  
      return out.modifies(as);
    };
  
    function initPath(path, pointRadius) {
      var prev = path.pointRadius();
      path.context(null);
      if (pointRadius != null) {
        path.pointRadius(pointRadius);
      }
      return prev;
    }
  
    /**
     * Geo-code a longitude/latitude point to an x/y coordinate.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(number, number): *} params.projection - The cartographic
     *   projection to apply.
     * @param {Array<function(object): *>} params.fields - A two-element array of
     *   field accessors for the longitude and latitude values.
     * @param {Array<string>} [params.as] - A two-element array of field names
     *   under which to store the result. Defaults to ['x','y'].
     */
    function GeoPoint(params) {
      Transform.call(this, null, params);
    }
  
    GeoPoint.Definition = {
      "type": "GeoPoint",
      "metadata": {"modifies": true},
      "params": [
        { "name": "projection", "type": "projection", "required": true },
        { "name": "fields", "type": "field", "array": true, "required": true, "length": 2 },
        { "name": "as", "type": "string", "array": true, "length": 2, "default": ["x", "y"] }
      ]
    };
  
    var prototype$13 = inherits(GeoPoint, Transform);
  
    prototype$13.transform = function(_, pulse) {
      var proj = _.projection,
          lon = _.fields[0],
          lat = _.fields[1],
          as = _.as || ['x', 'y'],
          x = as[0],
          y = as[1],
          mod;
  
      function set(t) {
        var xy = proj([lon(t), lat(t)]);
        if (xy) {
          t[x] = xy[0];
          t[y] = xy[1];
        } else {
          t[x] = undefined;
          t[y] = undefined;
        }
      }
  
      if (_.modified()) {
        // parameters updated, reflow
        pulse = pulse.materialize().reflow(true).visit(pulse.SOURCE, set);
      } else {
        mod = pulse.modified(lon.fields) || pulse.modified(lat.fields);
        pulse.visit(mod ? pulse.ADD_MOD : pulse.ADD, set);
      }
  
      return pulse.modifies(as);
    };
  
    /**
     * Annotate items with a geopath shape generator.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(number, number): *} params.projection - The cartographic
     *   projection to apply.
     * @param {function(object): *} [params.field] - The field with GeoJSON data,
     *   or null if the tuple itself is a GeoJSON feature.
     * @param {string} [params.as='shape'] - The output field in which to store
     *   the generated path data (default 'shape').
     */
    function GeoShape(params) {
      Transform.call(this, null, params);
    }
  
    GeoShape.Definition = {
      "type": "GeoShape",
      "metadata": {"modifies": true, "nomod": true},
      "params": [
        { "name": "projection", "type": "projection" },
        { "name": "field", "type": "field", "default": "datum" },
        { "name": "pointRadius", "type": "number", "expr": true },
        { "name": "as", "type": "string", "default": "shape" }
      ]
    };
  
    var prototype$14 = inherits(GeoShape, Transform);
  
    prototype$14.transform = function(_, pulse) {
      var out = pulse.fork(pulse.ALL),
          shape = this.value,
          as = _.as || 'shape',
          flag = out.ADD;
  
      if (!shape || _.modified()) {
        // parameters updated, reset and reflow
        this.value = shape = shapeGenerator(
          getProjectionPath(_.projection),
          _.field || field('datum'),
          _.pointRadius
        );
        out.materialize().reflow();
        flag = out.SOURCE;
      }
  
      out.visit(flag, function(t) { t[as] = shape; });
  
      return out.modifies(as);
    };
  
    function shapeGenerator(path, field, pointRadius) {
      var shape = pointRadius == null
        ? function(_) { return path(field(_)); }
        : function(_) {
          var prev = path.pointRadius(),
              value = path.pointRadius(pointRadius)(field(_));
          path.pointRadius(prev);
          return value;
        };
      shape.context = function(_) {
        path.context(_);
        return shape;
      };
  
      return shape;
    }
  
    /**
     * GeoJSON feature generator for creating graticules.
     * @constructor
     */
    function Graticule(params) {
      Transform.call(this, [], params);
      this.generator = d3Geo.geoGraticule();
    }
  
    Graticule.Definition = {
      "type": "Graticule",
      "metadata": {"changes": true},
      "params": [
        { "name": "extent", "type": "array", "array": true, "length": 2,
          "content": {"type": "number", "array": true, "length": 2} },
        { "name": "extentMajor", "type": "array", "array": true, "length": 2,
          "content": {"type": "number", "array": true, "length": 2} },
        { "name": "extentMinor", "type": "array", "array": true, "length": 2,
          "content": {"type": "number", "array": true, "length": 2} },
        { "name": "step", "type": "number", "array": true, "length": 2 },
        { "name": "stepMajor", "type": "number", "array": true, "length": 2, "default": [90, 360] },
        { "name": "stepMinor", "type": "number", "array": true, "length": 2, "default": [10, 10] },
        { "name": "precision", "type": "number", "default": 2.5 }
      ]
    };
  
    var prototype$15 = inherits(Graticule, Transform);
  
    prototype$15.transform = function(_, pulse) {
      var src = this.value,
          gen = this.generator, t;
  
      if (!src.length || _.modified()) {
        for (var prop in _) {
          if (isFunction(gen[prop])) {
            gen[prop](_[prop]);
          }
        }
      }
  
      t = gen();
      if (src.length) {
        pulse.mod.push(replace(src[0], t));
      } else {
        pulse.add.push(ingest(t));
      }
      src[0] = t;
  
      return pulse;
    };
  
    /**
     * Maintains a cartographic projection.
     * @constructor
     * @param {object} params - The parameters for this operator.
     */
    function Projection(params) {
      Transform.call(this, null, params);
      this.modified(true); // always treat as modified
    }
  
    var prototype$16 = inherits(Projection, Transform);
  
    prototype$16.transform = function(_, pulse) {
      var proj = this.value;
  
      if (!proj || _.modified('type')) {
        this.value = (proj = create$2(_.type));
        projectionProperties.forEach(function(prop) {
          if (_[prop] != null) set$1(proj, prop, _[prop]);
        });
      } else {
        projectionProperties.forEach(function(prop) {
          if (_.modified(prop)) set$1(proj, prop, _[prop]);
        });
      }
  
      if (_.pointRadius != null) proj.path.pointRadius(_.pointRadius);
      if (_.fit) fit(proj, _);
  
      return pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);
    };
  
    function fit(proj, _) {
      var data = collectGeoJSON(_.fit);
      _.extent ? proj.fitExtent(_.extent, data)
        : _.size ? proj.fitSize(_.size, data) : 0;
    }
  
    function create$2(type) {
      var constructor = projection((type || 'mercator').toLowerCase());
      if (!constructor) error('Unrecognized projection type: ' + type);
      return constructor();
    }
  
    function set$1(proj, key, value) {
       if (isFunction(proj[key])) proj[key](value);
    }
  
    function collectGeoJSON(data) {
      data = array(data);
      return data.length === 1 ? data[0]
        : {
            type: FeatureCollection,
            features: data.reduce((a, f) => a.concat(featurize(f)), [])
          };
    }
  
    function featurize(f) {
      return f.type === FeatureCollection
        ? f.features
        : array(f).filter(d => d != null).map(
            d => d.type === Feature ? d : {type: Feature, geometry: d}
          );
    }
  
  
  
    var geo = /*#__PURE__*/Object.freeze({
      contour: Contour,
      geojson: GeoJSON,
      geopath: GeoPath,
      geopoint: GeoPoint,
      geoshape: GeoShape,
      graticule: Graticule,
      projection: Projection
    });
  
    var ForceMap = {
      center: d3Force.forceCenter,
      collide: d3Force.forceCollide,
      nbody: d3Force.forceManyBody,
      link: d3Force.forceLink,
      x: d3Force.forceX,
      y: d3Force.forceY
    };
  
    var Forces = 'forces',
        ForceParams = [
          'alpha', 'alphaMin', 'alphaTarget',
          'velocityDecay', 'forces'
        ],
        ForceConfig = ['static', 'iterations'],
        ForceOutput = ['x', 'y', 'vx', 'vy'];
  
    /**
     * Force simulation layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<object>} params.forces - The forces to apply.
     */
    function Force(params) {
      Transform.call(this, null, params);
    }
  
    Force.Definition = {
      "type": "Force",
      "metadata": {"modifies": true},
      "params": [
        { "name": "static", "type": "boolean", "default": false },
        { "name": "restart", "type": "boolean", "default": false },
        { "name": "iterations", "type": "number", "default": 300 },
        { "name": "alpha", "type": "number", "default": 1 },
        { "name": "alphaMin", "type": "number", "default": 0.001 },
        { "name": "alphaTarget", "type": "number", "default": 0 },
        { "name": "velocityDecay", "type": "number", "default": 0.4 },
        { "name": "forces", "type": "param", "array": true,
          "params": [
            {
              "key": {"force": "center"},
              "params": [
                { "name": "x", "type": "number", "default": 0 },
                { "name": "y", "type": "number", "default": 0 }
              ]
            },
            {
              "key": {"force": "collide"},
              "params": [
                { "name": "radius", "type": "number", "expr": true },
                { "name": "strength", "type": "number", "default": 0.7 },
                { "name": "iterations", "type": "number", "default": 1 }
              ]
            },
            {
              "key": {"force": "nbody"},
              "params": [
                { "name": "strength", "type": "number", "default": -30 },
                { "name": "theta", "type": "number", "default": 0.9 },
                { "name": "distanceMin", "type": "number", "default": 1 },
                { "name": "distanceMax", "type": "number" }
              ]
            },
            {
              "key": {"force": "link"},
              "params": [
                { "name": "links", "type": "data" },
                { "name": "id", "type": "field" },
                { "name": "distance", "type": "number", "default": 30, "expr": true },
                { "name": "strength", "type": "number", "expr": true },
                { "name": "iterations", "type": "number", "default": 1 }
              ]
            },
            {
              "key": {"force": "x"},
              "params": [
                { "name": "strength", "type": "number", "default": 0.1 },
                { "name": "x", "type": "field" }
              ]
            },
            {
              "key": {"force": "y"},
              "params": [
                { "name": "strength", "type": "number", "default": 0.1 },
                { "name": "y", "type": "field" }
              ]
            }
          ] },
        {
          "name": "as", "type": "string", "array": true, "modify": false,
          "default": ForceOutput
        }
      ]
    };
  
    var prototype$17 = inherits(Force, Transform);
  
    prototype$17.transform = function(_, pulse) {
      var sim = this.value,
          change = pulse.changed(pulse.ADD_REM),
          params = _.modified(ForceParams),
          iters = _.iterations || 300;
  
      // configure simulation
      if (!sim) {
        this.value = sim = simulation(pulse.source, _);
        sim.on('tick', rerun(pulse.dataflow, this));
        if (!_.static) {
          change = true;
          sim.tick(); // ensure we run on init
        }
        pulse.modifies('index');
      } else {
        if (change) {
          pulse.modifies('index');
          sim.nodes(pulse.source);
        }
        if (params || pulse.changed(pulse.MOD)) {
          setup(sim, _, 0, pulse);
        }
      }
  
      // run simulation
      if (params || change || _.modified(ForceConfig)
          || (pulse.changed() && _.restart))
      {
        sim.alpha(Math.max(sim.alpha(), _.alpha || 1))
           .alphaDecay(1 - Math.pow(sim.alphaMin(), 1 / iters));
  
        if (_.static) {
          for (sim.stop(); --iters >= 0;) sim.tick();
        } else {
          if (sim.stopped()) sim.restart();
          if (!change) return pulse.StopPropagation; // defer to sim ticks
        }
      }
  
      return this.finish(_, pulse);
    };
  
    prototype$17.finish = function(_, pulse) {
      var dataflow = pulse.dataflow;
  
      // inspect dependencies, touch link source data
      for (var args=this._argops, j=0, m=args.length, arg; j<m; ++j) {
        arg = args[j];
        if (arg.name !== Forces || arg.op._argval.force !== 'link') {
          continue;
        }
        for (var ops=arg.op._argops, i=0, n=ops.length, op; i<n; ++i) {
          if (ops[i].name === 'links' && (op = ops[i].op.source)) {
            dataflow.pulse(op, dataflow.changeset().reflow());
            break;
          }
        }
      }
  
      // reflow all nodes
      return pulse.reflow(_.modified()).modifies(ForceOutput);
    };
  
    function rerun(df, op) {
      return function() { df.touch(op).run(); }
    }
  
    function simulation(nodes, _) {
      var sim = d3Force.forceSimulation(nodes),
          stopped = false,
          stop = sim.stop,
          restart = sim.restart;
  
      sim.stopped = function() {
        return stopped;
      };
      sim.restart = function() {
        stopped = false;
        return restart();
      };
      sim.stop = function() {
        stopped = true;
        return stop();
      };
  
      return setup(sim, _, true).on('end', function() { stopped = true; });
    }
  
    function setup(sim, _, init, pulse) {
      var f = array(_.forces), i, n, p, name;
  
      for (i=0, n=ForceParams.length; i<n; ++i) {
        p = ForceParams[i];
        if (p !== Forces && _.modified(p)) sim[p](_[p]);
      }
  
      for (i=0, n=f.length; i<n; ++i) {
        name = Forces + i;
        p = init || _.modified(Forces, i) ? getForce(f[i])
          : pulse && modified(f[i], pulse) ? sim.force(name)
          : null;
        if (p) sim.force(name, p);
      }
  
      for (n=(sim.numForces || 0); i<n; ++i) {
        sim.force(Forces + i, null); // remove
      }
  
      sim.numForces = f.length;
      return sim;
    }
  
    function modified(f, pulse) {
      var k, v;
      for (k in f) {
        if (isFunction(v = f[k]) && pulse.modified(accessorFields(v)))
          return 1;
      }
      return 0;
    }
  
    function getForce(_) {
      var f, p;
  
      if (!ForceMap.hasOwnProperty(_.force)) {
        error('Unrecognized force: ' + _.force);
      }
      f = ForceMap[_.force]();
  
      for (p in _) {
        if (isFunction(f[p])) setForceParam(f[p], _[p], _);
      }
  
      return f;
    }
  
    function setForceParam(f, v, _) {
      f(isFunction(v) ? function(d) { return v(d, _); } : v);
    }
  
  
  
    var force = /*#__PURE__*/Object.freeze({
      force: Force
    });
  
    // Build lookup table mapping tuple keys to tree node instances
    function lookup$3(tree, key, filter) {
      var map = {};
      tree.each(function(node) {
        var t = node.data;
        if (filter(t)) map[key(t)] = node;
      });
      tree.lookup = map;
      return tree;
    }
  
    /**
      * Nest tuples into a tree structure, grouped by key values.
      * @constructor
      * @param {object} params - The parameters for this operator.
      * @param {Array<function(object): *>} params.keys - The key fields to nest by, in order.
      * @param {boolean} [params.generate=false] - A boolean flag indicating if
      *   non-leaf nodes generated by this transform should be included in the
      *   output. The default (false) includes only the input data (leaf nodes)
      *   in the data stream.
      */
    function Nest(params) {
      Transform.call(this, null, params);
    }
  
    Nest.Definition = {
      "type": "Nest",
      "metadata": {"treesource": true, "changes": true},
      "params": [
        { "name": "keys", "type": "field", "array": true },
        { "name": "generate", "type": "boolean" }
      ]
    };
  
    var prototype$18 = inherits(Nest, Transform);
  
    function children(n) {
      return n.values;
    }
  
    prototype$18.transform = function(_, pulse) {
      if (!pulse.source) {
        error('Nest transform requires an upstream data source.');
      }
  
      var gen = _.generate,
          mod = _.modified(),
          out = pulse.clone(),
          tree = this.value;
  
      if (!tree || mod || pulse.changed()) {
        // collect nodes to remove
        if (tree) {
          tree.each(function(node) {
            if (node.children && isTuple(node.data)) {
              out.rem.push(node.data);
            }
          });
        }
  
        // generate new tree structure
        this.value = tree = d3Hierarchy.hierarchy({
          values: array(_.keys)
                    .reduce(function(n, k) { n.key(k); return n; }, nest())
                    .entries(out.source)
        }, children);
  
        // collect nodes to add
        if (gen) {
          tree.each(function(node) {
            if (node.children) {
              node = ingest(node.data);
              out.add.push(node);
              out.source.push(node);
            }
          });
        }
  
        // build lookup table
        lookup$3(tree, tupleid, tupleid);
      }
  
      out.source.root = tree;
      return out;
    };
  
    function nest() {
      var keys = [],
          nest;
  
      function apply(array, depth) {
        if (depth >= keys.length) {
          return array;
        }
  
        var i = -1,
            n = array.length,
            key = keys[depth++],
            keyValue,
            value,
            valuesByKey = {},
            values,
            result = {};
  
        while (++i < n) {
          keyValue = key(value = array[i]) + '';
          if (values = valuesByKey[keyValue]) {
            values.push(value);
          } else {
            valuesByKey[keyValue] = [value];
          }
        }
  
        for (keyValue in valuesByKey) {
          result[keyValue] = apply(valuesByKey[keyValue], depth);
        }
  
        return result;
      }
  
      function entries(map, depth) {
        if (++depth > keys.length) return map;
        var array = [], k;
        for (k in map) {
          array.push({key: k, values: entries(map[k], depth)});
        }
        return array;
      }
  
      return nest = {
        entries: function(array) { return entries(apply(array, 0), 0); },
        key: function(d) { keys.push(d); return nest; }
      };
    }
  
    /**
     * Abstract class for tree layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     */
    function HierarchyLayout(params) {
      Transform.call(this, null, params);
    }
  
    var prototype$19 = inherits(HierarchyLayout, Transform);
  
    prototype$19.transform = function(_, pulse) {
      if (!pulse.source || !pulse.source.root) {
        error(this.constructor.name
          + ' transform requires a backing tree data source.');
      }
  
      var layout = this.layout(_.method),
          fields = this.fields,
          root = pulse.source.root,
          as = _.as || fields;
  
      if (_.field) root.sum(_.field);
      if (_.sort) root.sort(_.sort);
  
      setParams(layout, this.params, _);
      if (layout.separation) {
        layout.separation(_.separation !== false ? defaultSeparation : one);
      }
  
      try {
        this.value = layout(root);
      } catch (err) {
        error(err);
      }
      root.each(function(node) { setFields(node, fields, as); });
  
      return pulse.reflow(_.modified()).modifies(as).modifies('leaf');
    };
  
    function setParams(layout, params, _) {
      for (var p, i=0, n=params.length; i<n; ++i) {
        p = params[i];
        if (p in _) layout[p](_[p]);
      }
    }
  
    function setFields(node, fields, as) {
      var t = node.data;
      for (var i=0, n=fields.length-1; i<n; ++i) {
        t[as[i]] = node[fields[i]];
      }
      t[as[n]] = node.children ? node.children.length : 0;
    }
  
    function defaultSeparation(a, b) {
      return a.parent === b.parent ? 1 : 2;
    }
  
    var Output = ['x', 'y', 'r', 'depth', 'children'];
  
    /**
     * Packed circle tree layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The value field to size nodes.
     */
    function Pack(params) {
      HierarchyLayout.call(this, params);
    }
  
    Pack.Definition = {
      "type": "Pack",
      "metadata": {"tree": true, "modifies": true},
      "params": [
        { "name": "field", "type": "field" },
        { "name": "sort", "type": "compare" },
        { "name": "padding", "type": "number", "default": 0 },
        { "name": "radius", "type": "field", "default": null },
        { "name": "size", "type": "number", "array": true, "length": 2 },
        { "name": "as", "type": "string", "array": true, "length": Output.length, "default": Output }
      ]
    };
  
    var prototype$1a = inherits(Pack, HierarchyLayout);
  
    prototype$1a.layout = d3Hierarchy.pack;
  
    prototype$1a.params = ['size', 'padding'];
  
    prototype$1a.fields = Output;
  
    var Output$1 = ['x0', 'y0', 'x1', 'y1', 'depth', 'children'];
  
    /**
     * Partition tree layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The value field to size nodes.
     */
    function Partition(params) {
      HierarchyLayout.call(this, params);
    }
  
    Partition.Definition = {
      "type": "Partition",
      "metadata": {"tree": true, "modifies": true},
      "params": [
        { "name": "field", "type": "field" },
        { "name": "sort", "type": "compare" },
        { "name": "padding", "type": "number", "default": 0 },
        { "name": "round", "type": "boolean", "default": false },
        { "name": "size", "type": "number", "array": true, "length": 2 },
        { "name": "as", "type": "string", "array": true, "length": Output$1.length, "default": Output$1 }
      ]
    };
  
    var prototype$1b = inherits(Partition, HierarchyLayout);
  
    prototype$1b.layout = d3Hierarchy.partition;
  
    prototype$1b.params = ['size', 'round', 'padding'];
  
    prototype$1b.fields = Output$1;
  
    /**
      * Stratify a collection of tuples into a tree structure based on
      * id and parent id fields.
      * @constructor
      * @param {object} params - The parameters for this operator.
      * @param {function(object): *} params.key - Unique key field for each tuple.
      * @param {function(object): *} params.parentKey - Field with key for parent tuple.
      */
    function Stratify(params) {
      Transform.call(this, null, params);
    }
  
    Stratify.Definition = {
      "type": "Stratify",
      "metadata": {"treesource": true},
      "params": [
        { "name": "key", "type": "field", "required": true },
        { "name": "parentKey", "type": "field", "required": true  }
      ]
    };
  
    var prototype$1c = inherits(Stratify, Transform);
  
    prototype$1c.transform = function(_, pulse) {
      if (!pulse.source) {
        error('Stratify transform requires an upstream data source.');
      }
  
      var tree = this.value,
          mod = _.modified(),
          out = pulse.fork(pulse.ALL).materialize(pulse.SOURCE),
          run = !this.value
             || mod
             || pulse.changed(pulse.ADD_REM)
             || pulse.modified(_.key.fields)
             || pulse.modified(_.parentKey.fields);
  
      // prevent upstream source pollution
      out.source = out.source.slice();
  
      if (run) {
        if (out.source.length) {
          tree = lookup$3(
            d3Hierarchy.stratify().id(_.key).parentId(_.parentKey)(out.source)
            , _.key, truthy);
        } else {
          tree = lookup$3(d3Hierarchy.stratify()([{}]), _.key, _.key);
        }
      }
  
      out.source.root = this.value = tree;
      return out;
    };
  
    var Layouts = {
      tidy: d3Hierarchy.tree,
      cluster: d3Hierarchy.cluster
    };
  
    var Output$2 = ['x', 'y', 'depth', 'children'];
  
    /**
     * Tree layout. Depending on the method parameter, performs either
     * Reingold-Tilford 'tidy' layout or dendrogram 'cluster' layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     */
    function Tree(params) {
      HierarchyLayout.call(this, params);
    }
  
    Tree.Definition = {
      "type": "Tree",
      "metadata": {"tree": true, "modifies": true},
      "params": [
        { "name": "field", "type": "field" },
        { "name": "sort", "type": "compare" },
        { "name": "method", "type": "enum", "default": "tidy", "values": ["tidy", "cluster"] },
        { "name": "size", "type": "number", "array": true, "length": 2 },
        { "name": "nodeSize", "type": "number", "array": true, "length": 2 },
        { "name": "separation", "type": "boolean", "default": true },
        { "name": "as", "type": "string", "array": true, "length": Output$2.length, "default": Output$2 }
      ]
    };
  
    var prototype$1d = inherits(Tree, HierarchyLayout);
  
    /**
     * Tree layout generator. Supports both 'tidy' and 'cluster' layouts.
     */
    prototype$1d.layout = function(method) {
      var m = method || 'tidy';
      if (Layouts.hasOwnProperty(m)) return Layouts[m]();
      else error('Unrecognized Tree layout method: ' + m);
    };
  
    prototype$1d.params = ['size', 'nodeSize'];
  
    prototype$1d.fields = Output$2;
  
    /**
      * Generate tuples representing links between tree nodes.
      * The resulting tuples will contain 'source' and 'target' fields,
      * which point to parent and child node tuples, respectively.
      * @constructor
      * @param {object} params - The parameters for this operator.
      */
    function TreeLinks(params) {
      Transform.call(this, [], params);
    }
  
    TreeLinks.Definition = {
      "type": "TreeLinks",
      "metadata": {"tree": true, "generates": true, "changes": true},
      "params": []
    };
  
    var prototype$1e = inherits(TreeLinks, Transform);
  
    prototype$1e.transform = function(_, pulse) {
      var links = this.value,
          tree = pulse.source && pulse.source.root,
          out = pulse.fork(pulse.NO_SOURCE),
          lut = {};
  
      if (!tree) error('TreeLinks transform requires a tree data source.');
  
      if (pulse.changed(pulse.ADD_REM)) {
        // remove previous links
        out.rem = links;
  
        // build lookup table of valid tuples
        pulse.visit(pulse.SOURCE, function(t) { lut[tupleid(t)] = 1; });
  
        // generate links for all edges incident on valid tuples
        tree.each(function(node) {
          var t = node.data,
              p = node.parent && node.parent.data;
          if (p && lut[tupleid(t)] && lut[tupleid(p)]) {
            out.add.push(ingest({source: p, target: t}));
          }
        });
        this.value = out.add;
      }
  
      else if (pulse.changed(pulse.MOD)) {
        // build lookup table of modified tuples
        pulse.visit(pulse.MOD, function(t) { lut[tupleid(t)] = 1; });
  
        // gather links incident on modified tuples
        links.forEach(function(link) {
          if (lut[tupleid(link.source)] || lut[tupleid(link.target)]) {
            out.mod.push(link);
          }
        });
      }
  
      return out;
    };
  
    var Tiles = {
      binary: d3Hierarchy.treemapBinary,
      dice: d3Hierarchy.treemapDice,
      slice: d3Hierarchy.treemapSlice,
      slicedice: d3Hierarchy.treemapSliceDice,
      squarify: d3Hierarchy.treemapSquarify,
      resquarify: d3Hierarchy.treemapResquarify
    };
  
    var Output$3 = ['x0', 'y0', 'x1', 'y1', 'depth', 'children'];
  
    /**
     * Treemap layout.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.field - The value field to size nodes.
     */
    function Treemap(params) {
      HierarchyLayout.call(this, params);
    }
  
    Treemap.Definition = {
      "type": "Treemap",
      "metadata": {"tree": true, "modifies": true},
      "params": [
        { "name": "field", "type": "field" },
        { "name": "sort", "type": "compare" },
        { "name": "method", "type": "enum", "default": "squarify",
          "values": ["squarify", "resquarify", "binary", "dice", "slice", "slicedice"] },
        { "name": "padding", "type": "number", "default": 0 },
        { "name": "paddingInner", "type": "number", "default": 0 },
        { "name": "paddingOuter", "type": "number", "default": 0 },
        { "name": "paddingTop", "type": "number", "default": 0 },
        { "name": "paddingRight", "type": "number", "default": 0 },
        { "name": "paddingBottom", "type": "number", "default": 0 },
        { "name": "paddingLeft", "type": "number", "default": 0 },
        { "name": "ratio", "type": "number", "default": 1.618033988749895 },
        { "name": "round", "type": "boolean", "default": false },
        { "name": "size", "type": "number", "array": true, "length": 2 },
        { "name": "as", "type": "string", "array": true, "length": Output$3.length, "default": Output$3 }
      ]
    };
  
    var prototype$1f = inherits(Treemap, HierarchyLayout);
  
    /**
     * Treemap layout generator. Adds 'method' and 'ratio' parameters
     * to configure the underlying tile method.
     */
    prototype$1f.layout = function() {
      var x = d3Hierarchy.treemap();
      x.ratio = function(_) {
        var t = x.tile();
        if (t.ratio) x.tile(t.ratio(_));
      };
      x.method = function(_) {
        if (Tiles.hasOwnProperty(_)) x.tile(Tiles[_]);
        else error('Unrecognized Treemap layout method: ' + _);
      };
      return x;
    };
  
    prototype$1f.params = [
      'method', 'ratio', 'size', 'round',
      'padding', 'paddingInner', 'paddingOuter',
      'paddingTop', 'paddingRight', 'paddingBottom', 'paddingLeft'
    ];
  
    prototype$1f.fields = Output$3;
  
  
  
    var tree = /*#__PURE__*/Object.freeze({
      nest: Nest,
      pack: Pack,
      partition: Partition,
      stratify: Stratify,
      tree: Tree,
      treelinks: TreeLinks,
      treemap: Treemap
    });
  
    function partition$3(data, groupby) {
      var groups = [],
          get = function(f) { return f(t); },
          map, i, n, t, k, g;
  
      // partition data points into stack groups
      if (groupby == null) {
        groups.push(data);
      } else {
        for (map={}, i=0, n=data.length; i<n; ++i) {
          t = data[i];
          k = groupby.map(get);
          g = map[k];
          if (!g) {
            map[k] = (g = []);
            g.dims = k;
            groups.push(g);
          }
          g.push(t);
        }
      }
  
      return groups;
    }
  
    /**
     * Compute locally-weighted regression fits for one or more data groups.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.x - An accessor for the predictor data field.
     * @param {function(object): *} params.y - An accessor for the predicted data field.
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors to groupby.
     * @param {number} [params.bandwidth=0.3] - The loess bandwidth.
     */
    function Loess(params) {
      Transform.call(this, null, params);
    }
  
    Loess.Definition = {
      "type": "Loess",
      "metadata": {"generates": true},
      "params": [
        { "name": "x", "type": "field", "required": true },
        { "name": "y", "type": "field", "required": true },
        { "name": "groupby", "type": "field", "array": true },
        { "name": "bandwidth", "type": "number", "default": 0.3 },
        { "name": "as", "type": "string", "array": true }
      ]
    };
  
    var prototype$1g = inherits(Loess, Transform);
  
    prototype$1g.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);
  
      if (!this.value || pulse.changed() || _.modified()) {
        const source = pulse.materialize(pulse.SOURCE).source,
              groups = partition$3(source, _.groupby),
              names = (_.groupby || []).map(accessorName),
              m = names.length,
              as = _.as || [accessorName(_.x), accessorName(_.y)],
              values = [];
  
        groups.forEach(g => {
          regressionLoess(g, _.x, _.y, _.bandwidth || 0.3).forEach(p => {
            const t = {};
            for (let i=0; i<m; ++i) {
              t[names[i]] = g.dims[i];
            }
            t[as[0]] = p[0];
            t[as[1]] = p[1];
            values.push(ingest(t));
          });
        });
  
        if (this.value) out.rem = this.value;
        this.value = out.add = out.source = values;
      }
  
      return out;
    };
  
    const Methods$1 = {
      linear: regressionLinear,
      log:    regressionLog,
      exp:    regressionExp,
      pow:    regressionPow,
      quad:   regressionQuad,
      poly:   regressionPoly
    };
  
    function degreesOfFreedom(method, order) {
      return method === 'poly' ? order : method === 'quad' ? 2 : 1;
    }
  
    /**
     * Compute regression fits for one or more data groups.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {function(object): *} params.x - An accessor for the predictor data field.
     * @param {function(object): *} params.y - An accessor for the predicted data field.
     * @param {string} [params.method='linear'] - The regression method to apply.
     * @param {Array<function(object): *>} [params.groupby] - An array of accessors to groupby.
     * @param {Array<number>} [params.extent] - The domain extent over which to plot the regression line.
     * @param {number} [params.order=3] - The polynomial order. Only applies to the 'poly' method.
     */
    function Regression(params) {
      Transform.call(this, null, params);
    }
  
    Regression.Definition = {
      "type": "Regression",
      "metadata": {"generates": true},
      "params": [
        { "name": "x", "type": "field", "required": true },
        { "name": "y", "type": "field", "required": true },
        { "name": "groupby", "type": "field", "array": true },
        { "name": "method", "type": "string", "default": "linear", "values": Object.keys(Methods$1) },
        { "name": "order", "type": "number", "default": 3 },
        { "name": "extent", "type": "number", "array": true, "length": 2 },
        { "name": "params", "type": "boolean", "default": false },
        { "name": "as", "type": "string", "array": true }
      ]
    };
  
    var prototype$1h = inherits(Regression, Transform);
  
    prototype$1h.transform = function(_, pulse) {
      var out = pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);
  
      if (!this.value || pulse.changed() || _.modified()) {
        const source = pulse.materialize(pulse.SOURCE).source,
              groups = partition$3(source, _.groupby),
              names = (_.groupby || []).map(accessorName),
              method = _.method || 'linear',
              order = _.order || 3,
              dof = degreesOfFreedom(method, order),
              as = _.as || [accessorName(_.x), accessorName(_.y)],
              fit = Methods$1[method],
              values = [];
  
        let domain = _.extent;
  
        if (!Methods$1.hasOwnProperty(method)) {
          error('Invalid regression method: ' + method);
        }
  
        if (domain != null) {
          if (method === 'log' && domain[0] <= 0) {
            pulse.dataflow.warn('Ignoring extent with values <= 0 for log regression.');
            domain = null;
          }
        }
  
        groups.forEach(g => {
          const n = g.length;
          if (n <= dof) {
            pulse.dataflow.warn('Skipping regression with more parameters than data points.');
            return;
          }
  
          const model = fit(g, _.x, _.y, order);
  
          if (_.params) {
            // if parameter vectors requested return those
            values.push(ingest({
              keys: g.dims,
              coef: model.coef,
              rSquared: model.rSquared
            }));
            return;
          }
  
          const dom = domain || extent(g, _.x),
                add = p => {
                  const t = {};
                  for (let i=0; i<names.length; ++i) {
                    t[names[i]] = g.dims[i];
                  }
                  t[as[0]] = p[0];
                  t[as[1]] = p[1];
                  values.push(ingest(t));
                };
  
          if (method === 'linear') {
            // for linear regression we only need the end points
            dom.forEach(x => add([x, model.predict(x)]));
          } else {
            // otherwise return trend line sample points
            sampleCurve(model.predict, dom, 25, 200).forEach(add);
          }
        });
  
        if (this.value) out.rem = this.value;
        this.value = out.add = out.source = values;
      }
  
      return out;
    };
  
  
  
    var reg = /*#__PURE__*/Object.freeze({
      loess: Loess,
      regression: Regression
    });
  
    function Voronoi(params) {
      Transform.call(this, null, params);
    }
  
    Voronoi.Definition = {
      "type": "Voronoi",
      "metadata": {"modifies": true},
      "params": [
        { "name": "x", "type": "field", "required": true },
        { "name": "y", "type": "field", "required": true },
        { "name": "size", "type": "number", "array": true, "length": 2 },
        { "name": "extent", "type": "array", "array": true, "length": 2,
          "default": [[-1e5, -1e5], [1e5, 1e5]],
          "content": {"type": "number", "array": true, "length": 2} },
        { "name": "as", "type": "string", "default": "path" }
      ]
    };
  
    var prototype$1i = inherits(Voronoi, Transform);
  
    var defaultExtent = [[-1e5, -1e5], [1e5, 1e5]];
  
    prototype$1i.transform = function(_, pulse) {
      var as = _.as || 'path',
          data = pulse.source,
          diagram, polygons, i, n;
  
      // configure and construct voronoi diagram
      diagram = d3Voronoi.voronoi().x(_.x).y(_.y);
      if (_.size) diagram.size(_.size);
      else diagram.extent(_.extent || defaultExtent);
  
      this.value = (diagram = diagram(data));
  
      // map polygons to paths
      polygons = diagram.polygons();
      for (i=0, n=data.length; i<n; ++i) {
        data[i][as] = polygons[i]
          ? 'M' + polygons[i].join('L') + 'Z'
          : null;
      }
  
      return pulse.reflow(_.modified()).modifies(as);
    };
  
  
  
    var voronoi = /*#__PURE__*/Object.freeze({
      voronoi: Voronoi
    });
  
    /*
    Copyright (c) 2013, Jason Davies.
    All rights reserved.
  
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:
  
      * Redistributions of source code must retain the above copyright notice, this
        list of conditions and the following disclaimer.
  
      * Redistributions in binary form must reproduce the above copyright notice,
        this list of conditions and the following disclaimer in the documentation
        and/or other materials provided with the distribution.
  
      * The name Jason Davies may not be used to endorse or promote products
        derived from this software without specific prior written permission.
  
    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    DISCLAIMED. IN NO EVENT SHALL JASON DAVIES BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
    LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
    OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
    ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
    */
  
    // Word cloud layout by Jason Davies, https://www.jasondavies.com/wordcloud/
    // Algorithm due to Jonathan Feinberg, http://static.mrfeinberg.com/bv_ch03.pdf
  
    var cloudRadians = Math.PI / 180,
        cw = 1 << 11 >> 5,
        ch = 1 << 11;
  
    function cloud() {
      var size = [256, 256],
          text,
          font,
          fontSize,
          fontStyle,
          fontWeight,
          rotate,
          padding,
          spiral = archimedeanSpiral,
          words = [],
          random = Math.random,
          cloud = {};
  
      cloud.layout = function() {
        var contextAndRatio = getContext(domCanvas()),
            board = zeroArray((size[0] >> 5) * size[1]),
            bounds = null,
            n = words.length,
            i = -1,
            tags = [],
            data = words.map(function(d) {
              return {
                text: text(d),
                font: font(d),
                style: fontStyle(d),
                weight: fontWeight(d),
                rotate: rotate(d),
                size: ~~fontSize(d),
                padding: padding(d),
                xoff: 0,
                yoff: 0,
                x1: 0,
                y1: 0,
                x0: 0,
                y0: 0,
                hasText: false,
                sprite: null,
                datum: d
              };
            }).sort(function(a, b) { return b.size - a.size; });
  
        while (++i < n) {
          var d = data[i];
          d.x = (size[0] * (random() + .5)) >> 1;
          d.y = (size[1] * (random() + .5)) >> 1;
          cloudSprite(contextAndRatio, d, data, i);
          if (d.hasText && place(board, d, bounds)) {
            tags.push(d);
            if (bounds) cloudBounds(bounds, d);
            else bounds = [{x: d.x + d.x0, y: d.y + d.y0}, {x: d.x + d.x1, y: d.y + d.y1}];
            // Temporary hack
            d.x -= size[0] >> 1;
            d.y -= size[1] >> 1;
          }
        }
  
        return tags;
      };
  
      function getContext(canvas) {
        canvas.width = canvas.height = 1;
        var ratio = Math.sqrt(canvas.getContext("2d").getImageData(0, 0, 1, 1).data.length >> 2);
        canvas.width = (cw << 5) / ratio;
        canvas.height = ch / ratio;
  
        var context = canvas.getContext("2d");
        context.fillStyle = context.strokeStyle = "red";
        context.textAlign = "center";
  
        return {context: context, ratio: ratio};
      }
  
      function place(board, tag, bounds) {
        var startX = tag.x,
            startY = tag.y,
            maxDelta = Math.sqrt(size[0] * size[0] + size[1] * size[1]),
            s = spiral(size),
            dt = random() < .5 ? 1 : -1,
            t = -dt,
            dxdy,
            dx,
            dy;
  
        while (dxdy = s(t += dt)) {
          dx = ~~dxdy[0];
          dy = ~~dxdy[1];
  
          if (Math.min(Math.abs(dx), Math.abs(dy)) >= maxDelta) break;
  
          tag.x = startX + dx;
          tag.y = startY + dy;
  
          if (tag.x + tag.x0 < 0 || tag.y + tag.y0 < 0 ||
              tag.x + tag.x1 > size[0] || tag.y + tag.y1 > size[1]) continue;
          // TODO only check for collisions within current bounds.
          if (!bounds || !cloudCollide(tag, board, size[0])) {
            if (!bounds || collideRects(tag, bounds)) {
              var sprite = tag.sprite,
                  w = tag.width >> 5,
                  sw = size[0] >> 5,
                  lx = tag.x - (w << 4),
                  sx = lx & 0x7f,
                  msx = 32 - sx,
                  h = tag.y1 - tag.y0,
                  x = (tag.y + tag.y0) * sw + (lx >> 5),
                  last;
              for (var j = 0; j < h; j++) {
                last = 0;
                for (var i = 0; i <= w; i++) {
                  board[x + i] |= (last << msx) | (i < w ? (last = sprite[j * w + i]) >>> sx : 0);
                }
                x += sw;
              }
              tag.sprite = null;
              return true;
            }
          }
        }
        return false;
      }
  
      cloud.words = function(_) {
        if (arguments.length) {
          words = _;
          return cloud;
        } else {
          return words;
        }
      };
  
      cloud.size = function(_) {
        if (arguments.length) {
          size = [+_[0], +_[1]];
          return cloud;
        } else {
          return size;
        }
      };
  
      cloud.font = function(_) {
        if (arguments.length) {
          font = functor(_);
          return cloud;
        } else {
          return font;
        }
      };
  
      cloud.fontStyle = function(_) {
        if (arguments.length) {
          fontStyle = functor(_);
          return cloud;
        } else {
          return fontStyle;
        }
      };
  
      cloud.fontWeight = function(_) {
        if (arguments.length) {
          fontWeight = functor(_);
          return cloud;
        } else {
          return fontWeight;
        }
      };
  
      cloud.rotate = function(_) {
        if (arguments.length) {
          rotate = functor(_);
          return cloud;
        } else {
          return rotate;
        }
      };
  
      cloud.text = function(_) {
        if (arguments.length) {
          text = functor(_);
          return cloud;
        } else {
          return text;
        }
      };
  
      cloud.spiral = function(_) {
        if (arguments.length) {
          spiral = spirals[_] || _;
          return cloud;
        } else {
          return spiral;
        }
      };
  
      cloud.fontSize = function(_) {
        if (arguments.length) {
          fontSize = functor(_);
          return cloud;
        } else {
          return fontSize;
        }
      };
  
      cloud.padding = function(_) {
        if (arguments.length) {
          padding = functor(_);
          return cloud;
        } else {
          return padding;
        }
      };
  
      cloud.random = function(_) {
        if (arguments.length) {
          random = _;
          return cloud;
        } else {
          return random;
        }
      };
  
      return cloud;
    }
  
    // Fetches a monochrome sprite bitmap for the specified text.
    // Load in batches for speed.
    function cloudSprite(contextAndRatio, d, data, di) {
      if (d.sprite) return;
      var c = contextAndRatio.context,
          ratio = contextAndRatio.ratio;
  
      c.clearRect(0, 0, (cw << 5) / ratio, ch / ratio);
      var x = 0,
          y = 0,
          maxh = 0,
          n = data.length,
          w, w32, h, i, j;
      --di;
      while (++di < n) {
        d = data[di];
        c.save();
        c.font = d.style + " " + d.weight + " " + ~~((d.size + 1) / ratio) + "px " + d.font;
        w = c.measureText(d.text + "m").width * ratio;
        h = d.size << 1;
        if (d.rotate) {
          var sr = Math.sin(d.rotate * cloudRadians),
              cr = Math.cos(d.rotate * cloudRadians),
              wcr = w * cr,
              wsr = w * sr,
              hcr = h * cr,
              hsr = h * sr;
          w = (Math.max(Math.abs(wcr + hsr), Math.abs(wcr - hsr)) + 0x1f) >> 5 << 5;
          h = ~~Math.max(Math.abs(wsr + hcr), Math.abs(wsr - hcr));
        } else {
          w = (w + 0x1f) >> 5 << 5;
        }
        if (h > maxh) maxh = h;
        if (x + w >= (cw << 5)) {
          x = 0;
          y += maxh;
          maxh = 0;
        }
        if (y + h >= ch) break;
        c.translate((x + (w >> 1)) / ratio, (y + (h >> 1)) / ratio);
        if (d.rotate) c.rotate(d.rotate * cloudRadians);
        c.fillText(d.text, 0, 0);
        if (d.padding) {
          c.lineWidth = 2 * d.padding;
          c.strokeText(d.text, 0, 0);
        }
        c.restore();
        d.width = w;
        d.height = h;
        d.xoff = x;
        d.yoff = y;
        d.x1 = w >> 1;
        d.y1 = h >> 1;
        d.x0 = -d.x1;
        d.y0 = -d.y1;
        d.hasText = true;
        x += w;
      }
      var pixels = c.getImageData(0, 0, (cw << 5) / ratio, ch / ratio).data,
          sprite = [];
      while (--di >= 0) {
        d = data[di];
        if (!d.hasText) continue;
        w = d.width;
        w32 = w >> 5;
        h = d.y1 - d.y0;
        // Zero the buffer
        for (i = 0; i < h * w32; i++) sprite[i] = 0;
        x = d.xoff;
        if (x == null) return;
        y = d.yoff;
        var seen = 0,
            seenRow = -1;
        for (j = 0; j < h; j++) {
          for (i = 0; i < w; i++) {
            var k = w32 * j + (i >> 5),
                m = pixels[((y + j) * (cw << 5) + (x + i)) << 2] ? 1 << (31 - (i % 32)) : 0;
            sprite[k] |= m;
            seen |= m;
          }
          if (seen) seenRow = j;
          else {
            d.y0++;
            h--;
            j--;
            y++;
          }
        }
        d.y1 = d.y0 + seenRow;
        d.sprite = sprite.slice(0, (d.y1 - d.y0) * w32);
      }
    }
  
    // Use mask-based collision detection.
    function cloudCollide(tag, board, sw) {
      sw >>= 5;
      var sprite = tag.sprite,
          w = tag.width >> 5,
          lx = tag.x - (w << 4),
          sx = lx & 0x7f,
          msx = 32 - sx,
          h = tag.y1 - tag.y0,
          x = (tag.y + tag.y0) * sw + (lx >> 5),
          last;
      for (var j = 0; j < h; j++) {
        last = 0;
        for (var i = 0; i <= w; i++) {
          if (((last << msx) | (i < w ? (last = sprite[j * w + i]) >>> sx : 0))
              & board[x + i]) return true;
        }
        x += sw;
      }
      return false;
    }
  
    function cloudBounds(bounds, d) {
      var b0 = bounds[0],
          b1 = bounds[1];
      if (d.x + d.x0 < b0.x) b0.x = d.x + d.x0;
      if (d.y + d.y0 < b0.y) b0.y = d.y + d.y0;
      if (d.x + d.x1 > b1.x) b1.x = d.x + d.x1;
      if (d.y + d.y1 > b1.y) b1.y = d.y + d.y1;
    }
  
    function collideRects(a, b) {
      return a.x + a.x1 > b[0].x && a.x + a.x0 < b[1].x && a.y + a.y1 > b[0].y && a.y + a.y0 < b[1].y;
    }
  
    function archimedeanSpiral(size) {
      var e = size[0] / size[1];
      return function(t) {
        return [e * (t *= .1) * Math.cos(t), t * Math.sin(t)];
      };
    }
  
    function rectangularSpiral(size) {
      var dy = 4,
          dx = dy * size[0] / size[1],
          x = 0,
          y = 0;
      return function(t) {
        var sign = t < 0 ? -1 : 1;
        // See triangular numbers: T_n = n * (n + 1) / 2.
        switch ((Math.sqrt(1 + 4 * sign * t) - sign) & 3) {
          case 0:  x += dx; break;
          case 1:  y += dy; break;
          case 2:  x -= dx; break;
          default: y -= dy; break;
        }
        return [x, y];
      };
    }
  
    // TODO reuse arrays?
    function zeroArray(n) {
      var a = [],
          i = -1;
      while (++i < n) a[i] = 0;
      return a;
    }
  
    function functor(d) {
      return typeof d === "function" ? d : function() { return d; };
    }
  
    var spirals = {
      archimedean: archimedeanSpiral,
      rectangular: rectangularSpiral
    };
  
    var Output$4 = ['x', 'y', 'font', 'fontSize', 'fontStyle', 'fontWeight', 'angle'];
  
    var Params$1 = ['text', 'font', 'rotate', 'fontSize', 'fontStyle', 'fontWeight'];
  
    function Wordcloud(params) {
      Transform.call(this, cloud(), params);
    }
  
    Wordcloud.Definition = {
      "type": "Wordcloud",
      "metadata": {"modifies": true},
      "params": [
        { "name": "size", "type": "number", "array": true, "length": 2 },
        { "name": "font", "type": "string", "expr": true, "default": "sans-serif" },
        { "name": "fontStyle", "type": "string", "expr": true, "default": "normal" },
        { "name": "fontWeight", "type": "string", "expr": true, "default": "normal" },
        { "name": "fontSize", "type": "number", "expr": true, "default": 14 },
        { "name": "fontSizeRange", "type": "number", "array": "nullable", "default": [10, 50] },
        { "name": "rotate", "type": "number", "expr": true, "default": 0 },
        { "name": "text", "type": "field" },
        { "name": "spiral", "type": "string", "values": ["archimedean", "rectangular"] },
        { "name": "padding", "type": "number", "expr": true },
        { "name": "as", "type": "string", "array": true, "length": 7, "default": Output$4 }
      ]
    };
  
    var prototype$1j = inherits(Wordcloud, Transform);
  
    prototype$1j.transform = function(_, pulse) {
      if (_.size && !(_.size[0] && _.size[1])) {
        error('Wordcloud size dimensions must be non-zero.');
      }
  
      function modp(param) {
        var p = _[param];
        return isFunction(p) && pulse.modified(p.fields);
      }
  
      var mod = _.modified();
      if (!(mod || pulse.changed(pulse.ADD_REM) || Params$1.some(modp))) return;
  
      var data = pulse.materialize(pulse.SOURCE).source,
          layout = this.value,
          as = _.as || Output$4,
          fontSize = _.fontSize || 14,
          range;
  
      isFunction(fontSize)
        ? (range = _.fontSizeRange)
        : (fontSize = constant(fontSize));
  
      // create font size scaling function as needed
      if (range) {
        var fsize = fontSize,
            sizeScale = scale$1('sqrt')()
              .domain(extent$1(fsize, data))
              .range(range);
        fontSize = function(x) { return sizeScale(fsize(x)); };
      }
  
      data.forEach(function(t) {
        t[as[0]] = NaN;
        t[as[1]] = NaN;
        t[as[3]] = 0;
      });
  
      // configure layout
      var words = layout
        .words(data)
        .text(_.text)
        .size(_.size || [500, 500])
        .padding(_.padding || 1)
        .spiral(_.spiral || 'archimedean')
        .rotate(_.rotate || 0)
        .font(_.font || 'sans-serif')
        .fontStyle(_.fontStyle || 'normal')
        .fontWeight(_.fontWeight || 'normal')
        .fontSize(fontSize)
        .random(exports.random)
        .layout();
  
      var size = layout.size(),
          dx = size[0] >> 1,
          dy = size[1] >> 1,
          i = 0,
          n = words.length,
          w, t;
  
      for (; i<n; ++i) {
        w = words[i];
        t = w.datum;
        t[as[0]] = w.x + dx;
        t[as[1]] = w.y + dy;
        t[as[2]] = w.font;
        t[as[3]] = w.size;
        t[as[4]] = w.style;
        t[as[5]] = w.weight;
        t[as[6]] = w.rotate;
      }
  
      return pulse.reflow(mod).modifies(as);
    };
  
    function extent$1(field, data) {
      var min = +Infinity,
          max = -Infinity,
          i = 0,
          n = data.length,
          v;
  
      for (; i<n; ++i) {
        v = field(data[i]);
        if (v < min) min = v;
        if (v > max) max = v;
      }
  
      return [min, max];
    }
  
  
  
    var wordcloud = /*#__PURE__*/Object.freeze({
      wordcloud: Wordcloud
    });
  
    function array8(n) { return new Uint8Array(n); }
  
    function array16(n) { return new Uint16Array(n); }
  
    function array32(n) { return new Uint32Array(n); }
  
    /**
     * Maintains CrossFilter state.
     */
    function Bitmaps() {
  
      var width = 8,
          data = [],
          seen = array32(0),
          curr = array$1(0, width),
          prev = array$1(0, width);
  
      return {
  
        data: function() { return data; },
  
        seen: function() {
          return (seen = lengthen(seen, data.length));
        },
  
        add: function(array) {
          for (var i=0, j=data.length, n=array.length, t; i<n; ++i) {
            t = array[i];
            t._index = j++;
            data.push(t);
          }
        },
  
        remove: function(num, map) { // map: index -> boolean (true => remove)
          var n = data.length,
              copy = Array(n - num),
              reindex = data, // reuse old data array for index map
              t, i, j;
  
          // seek forward to first removal
          for (i=0; !map[i] && i<n; ++i) {
            copy[i] = data[i];
            reindex[i] = i;
          }
  
          // condense arrays
          for (j=i; i<n; ++i) {
            t = data[i];
            if (!map[i]) {
              reindex[i] = j;
              curr[j] = curr[i];
              prev[j] = prev[i];
              copy[j] = t;
              t._index = j++;
            } else {
              reindex[i] = -1;
            }
            curr[i] = 0; // clear unused bits
          }
  
          data = copy;
          return reindex;
        },
  
        size: function() { return data.length; },
  
        curr: function() { return curr; },
  
        prev: function() { return prev; },
  
        reset: function(k) { prev[k] = curr[k]; },
  
        all: function() {
          return width < 0x101 ? 0xff : width < 0x10001 ? 0xffff : 0xffffffff;
        },
  
        set: function(k, one) { curr[k] |= one; },
  
        clear: function(k, one) { curr[k] &= ~one; },
  
        resize: function(n, m) {
          var k = curr.length;
          if (n > k || m > width) {
            width = Math.max(m, width);
            curr = array$1(n, width, curr);
            prev = array$1(n, width);
          }
        }
      };
    }
  
    function lengthen(array, length, copy) {
      if (array.length >= length) return array;
      copy = copy || new array.constructor(length);
      copy.set(array);
      return copy;
    }
  
    function array$1(n, m, array) {
      var copy = (m < 0x101 ? array8 : m < 0x10001 ? array16 : array32)(n);
      if (array) copy.set(array);
      return copy;
    }
  
    function Dimension(index, i, query) {
      var bit = (1 << i);
  
      return {
        one:     bit,
        zero:    ~bit,
        range:   query.slice(),
        bisect:  index.bisect,
        index:   index.index,
        size:    index.size,
  
        onAdd: function(added, curr) {
          var dim = this,
              range = dim.bisect(dim.range, added.value),
              idx = added.index,
              lo = range[0],
              hi = range[1],
              n1 = idx.length, i;
  
          for (i=0;  i<lo; ++i) curr[idx[i]] |= bit;
          for (i=hi; i<n1; ++i) curr[idx[i]] |= bit;
          return dim;
        }
      };
    }
  
    /**
     * Maintains a list of values, sorted by key.
     */
    function SortedIndex() {
      var index = array32(0),
          value = [],
          size = 0;
  
      function insert(key, data, base) {
        if (!data.length) return [];
  
        var n0 = size,
            n1 = data.length,
            addv = Array(n1),
            addi = array32(n1),
            oldv, oldi, i;
  
        for (i=0; i<n1; ++i) {
          addv[i] = key(data[i]);
          addi[i] = i;
        }
        addv = sort(addv, addi);
  
        if (n0) {
          oldv = value;
          oldi = index;
          value = Array(n0 + n1);
          index = array32(n0 + n1);
          merge$1(base, oldv, oldi, n0, addv, addi, n1, value, index);
        } else {
          if (base > 0) for (i=0; i<n1; ++i) {
            addi[i] += base;
          }
          value = addv;
          index = addi;
        }
        size = n0 + n1;
  
        return {index: addi, value: addv};
      }
  
      function remove(num, map) {
        // map: index -> remove
        var n = size,
            idx, i, j;
  
        // seek forward to first removal
        for (i=0; !map[index[i]] && i<n; ++i);
  
        // condense index and value arrays
        for (j=i; i<n; ++i) {
          if (!map[idx=index[i]]) {
            index[j] = idx;
            value[j] = value[i];
            ++j;
          }
        }
  
        size = n - num;
      }
  
      function reindex(map) {
        for (var i=0, n=size; i<n; ++i) {
          index[i] = map[index[i]];
        }
      }
  
      function bisect(range, array) {
        var n;
        if (array) {
          n = array.length;
        } else {
          array = value;
          n = size;
        }
        return [
          d3Array.bisectLeft(array, range[0], 0, n),
          d3Array.bisectRight(array, range[1], 0, n)
        ];
      }
  
      return {
        insert:  insert,
        remove:  remove,
        bisect:  bisect,
        reindex: reindex,
        index:   function() { return index; },
        size:    function() { return size; }
      };
    }
  
    function sort(values, index) {
      values.sort.call(index, function(a, b) {
        var x = values[a],
            y = values[b];
        return x < y ? -1 : x > y ? 1 : 0;
      });
      return d3Array.permute(values, index);
    }
  
    function merge$1(base, value0, index0, n0, value1, index1, n1, value, index) {
      var i0 = 0, i1 = 0, i;
  
      for (i=0; i0 < n0 && i1 < n1; ++i) {
        if (value0[i0] < value1[i1]) {
          value[i] = value0[i0];
          index[i] = index0[i0++];
        } else {
          value[i] = value1[i1];
          index[i] = index1[i1++] + base;
        }
      }
  
      for (; i0 < n0; ++i0, ++i) {
        value[i] = value0[i0];
        index[i] = index0[i0];
      }
  
      for (; i1 < n1; ++i1, ++i) {
        value[i] = value1[i1];
        index[i] = index1[i1] + base;
      }
    }
  
    /**
     * An indexed multi-dimensional filter.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {Array<function(object): *>} params.fields - An array of dimension accessors to filter.
     * @param {Array} params.query - An array of per-dimension range queries.
     */
    function CrossFilter(params) {
      Transform.call(this, Bitmaps(), params);
      this._indices = null;
      this._dims = null;
    }
  
    CrossFilter.Definition = {
      "type": "CrossFilter",
      "metadata": {},
      "params": [
        { "name": "fields", "type": "field", "array": true, "required": true },
        { "name": "query", "type": "array", "array": true, "required": true,
          "content": {"type": "number", "array": true, "length": 2} }
      ]
    };
  
    var prototype$1k = inherits(CrossFilter, Transform);
  
    prototype$1k.transform = function(_, pulse) {
      if (!this._dims) {
        return this.init(_, pulse);
      } else {
        var init = _.modified('fields')
              || _.fields.some(function(f) { return pulse.modified(f.fields); });
  
        return init
          ? this.reinit(_, pulse)
          : this.eval(_, pulse);
      }
    };
  
    prototype$1k.init = function(_, pulse) {
      var fields = _.fields,
          query = _.query,
          indices = this._indices = {},
          dims = this._dims = [],
          m = query.length,
          i = 0, key, index;
  
      // instantiate indices and dimensions
      for (; i<m; ++i) {
        key = fields[i].fname;
        index = indices[key] || (indices[key] = SortedIndex());
        dims.push(Dimension(index, i, query[i]));
      }
  
      return this.eval(_, pulse);
    };
  
    prototype$1k.reinit = function(_, pulse) {
      var output = pulse.materialize().fork(),
          fields = _.fields,
          query = _.query,
          indices = this._indices,
          dims = this._dims,
          bits = this.value,
          curr = bits.curr(),
          prev = bits.prev(),
          all = bits.all(),
          out = (output.rem = output.add),
          mod = output.mod,
          m = query.length,
          adds = {}, add, index, key,
          mods, remMap, modMap, i, n, f;
  
      // set prev to current state
      prev.set(curr);
  
      // if pulse has remove tuples, process them first
      if (pulse.rem.length) {
        remMap = this.remove(_, pulse, output);
      }
  
      // if pulse has added tuples, add them to state
      if (pulse.add.length) {
        bits.add(pulse.add);
      }
  
      // if pulse has modified tuples, create an index map
      if (pulse.mod.length) {
        modMap = {};
        for (mods=pulse.mod, i=0, n=mods.length; i<n; ++i) {
          modMap[mods[i]._index] = 1;
        }
      }
  
      // re-initialize indices as needed, update curr bitmap
      for (i=0; i<m; ++i) {
        f = fields[i];
        if (!dims[i] || _.modified('fields', i) || pulse.modified(f.fields)) {
          key = f.fname;
          if (!(add = adds[key])) {
            indices[key] = index = SortedIndex();
            adds[key] = add = index.insert(f, pulse.source, 0);
          }
          dims[i] = Dimension(index, i, query[i]).onAdd(add, curr);
        }
      }
  
      // visit each tuple
      // if filter state changed, push index to add/rem
      // else if in mod and passes a filter, push index to mod
      for (i=0, n=bits.data().length; i<n; ++i) {
        if (remMap[i]) { // skip if removed tuple
          continue;
        } else if (prev[i] !== curr[i]) { // add if state changed
          out.push(i);
        } else if (modMap[i] && curr[i] !== all) { // otherwise, pass mods through
          mod.push(i);
        }
      }
  
      bits.mask = (1 << m) - 1;
      return output;
    };
  
    prototype$1k.eval = function(_, pulse) {
      var output = pulse.materialize().fork(),
          m = this._dims.length,
          mask = 0;
  
      if (pulse.rem.length) {
        this.remove(_, pulse, output);
        mask |= (1 << m) - 1;
      }
  
      if (_.modified('query') && !_.modified('fields')) {
        mask |= this.update(_, pulse, output);
      }
  
      if (pulse.add.length) {
        this.insert(_, pulse, output);
        mask |= (1 << m) - 1;
      }
  
      if (pulse.mod.length) {
        this.modify(pulse, output);
        mask |= (1 << m) - 1;
      }
  
      this.value.mask = mask;
      return output;
    };
  
    prototype$1k.insert = function(_, pulse, output) {
      var tuples = pulse.add,
          bits = this.value,
          dims = this._dims,
          indices = this._indices,
          fields = _.fields,
          adds = {},
          out = output.add,
          k = bits.size(),
          n = k + tuples.length,
          m = dims.length, j, key, add;
  
      // resize bitmaps and add tuples as needed
      bits.resize(n, m);
      bits.add(tuples);
  
      var curr = bits.curr(),
          prev = bits.prev(),
          all  = bits.all();
  
      // add to dimensional indices
      for (j=0; j<m; ++j) {
        key = fields[j].fname;
        add = adds[key] || (adds[key] = indices[key].insert(fields[j], tuples, k));
        dims[j].onAdd(add, curr);
      }
  
      // set previous filters, output if passes at least one filter
      for (; k<n; ++k) {
        prev[k] = all;
        if (curr[k] !== all) out.push(k);
      }
    };
  
    prototype$1k.modify = function(pulse, output) {
      var out = output.mod,
          bits = this.value,
          curr = bits.curr(),
          all  = bits.all(),
          tuples = pulse.mod,
          i, n, k;
  
      for (i=0, n=tuples.length; i<n; ++i) {
        k = tuples[i]._index;
        if (curr[k] !== all) out.push(k);
      }
    };
  
    prototype$1k.remove = function(_, pulse, output) {
      var indices = this._indices,
          bits = this.value,
          curr = bits.curr(),
          prev = bits.prev(),
          all  = bits.all(),
          map = {},
          out = output.rem,
          tuples = pulse.rem,
          i, n, k, f;
  
      // process tuples, output if passes at least one filter
      for (i=0, n=tuples.length; i<n; ++i) {
        k = tuples[i]._index;
        map[k] = 1; // build index map
        prev[k] = (f = curr[k]);
        curr[k] = all;
        if (f !== all) out.push(k);
      }
  
      // remove from dimensional indices
      for (k in indices) {
        indices[k].remove(n, map);
      }
  
      this.reindex(pulse, n, map);
      return map;
    };
  
    // reindex filters and indices after propagation completes
    prototype$1k.reindex = function(pulse, num, map) {
      var indices = this._indices,
          bits = this.value;
  
      pulse.runAfter(function() {
        var indexMap = bits.remove(num, map);
        for (var key in indices) indices[key].reindex(indexMap);
      });
    };
  
    prototype$1k.update = function(_, pulse, output) {
      var dims = this._dims,
          query = _.query,
          stamp = pulse.stamp,
          m = dims.length,
          mask = 0, i, q;
  
      // survey how many queries have changed
      output.filters = 0;
      for (q=0; q<m; ++q) {
        if (_.modified('query', q)) { i = q; ++mask; }
      }
  
      if (mask === 1) {
        // only one query changed, use more efficient update
        mask = dims[i].one;
        this.incrementOne(dims[i], query[i], output.add, output.rem);
      } else {
        // multiple queries changed, perform full record keeping
        for (q=0, mask=0; q<m; ++q) {
          if (!_.modified('query', q)) continue;
          mask |= dims[q].one;
          this.incrementAll(dims[q], query[q], stamp, output.add);
          output.rem = output.add; // duplicate add/rem for downstream resolve
        }
      }
  
      return mask;
    };
  
    prototype$1k.incrementAll = function(dim, query, stamp, out) {
      var bits = this.value,
          seen = bits.seen(),
          curr = bits.curr(),
          prev = bits.prev(),
          index = dim.index(),
          old = dim.bisect(dim.range),
          range = dim.bisect(query),
          lo1 = range[0],
          hi1 = range[1],
          lo0 = old[0],
          hi0 = old[1],
          one = dim.one,
          i, j, k;
  
      // Fast incremental update based on previous lo index.
      if (lo1 < lo0) {
        for (i = lo1, j = Math.min(lo0, hi1); i < j; ++i) {
          k = index[i];
          if (seen[k] !== stamp) {
            prev[k] = curr[k];
            seen[k] = stamp;
            out.push(k);
          }
          curr[k] ^= one;
        }
      } else if (lo1 > lo0) {
        for (i = lo0, j = Math.min(lo1, hi0); i < j; ++i) {
          k = index[i];
          if (seen[k] !== stamp) {
            prev[k] = curr[k];
            seen[k] = stamp;
            out.push(k);
          }
          curr[k] ^= one;
        }
      }
  
      // Fast incremental update based on previous hi index.
      if (hi1 > hi0) {
        for (i = Math.max(lo1, hi0), j = hi1; i < j; ++i) {
          k = index[i];
          if (seen[k] !== stamp) {
            prev[k] = curr[k];
            seen[k] = stamp;
            out.push(k);
          }
          curr[k] ^= one;
        }
      } else if (hi1 < hi0) {
        for (i = Math.max(lo0, hi1), j = hi0; i < j; ++i) {
          k = index[i];
          if (seen[k] !== stamp) {
            prev[k] = curr[k];
            seen[k] = stamp;
            out.push(k);
          }
          curr[k] ^= one;
        }
      }
  
      dim.range = query.slice();
    };
  
    prototype$1k.incrementOne = function(dim, query, add, rem) {
      var bits = this.value,
          curr = bits.curr(),
          index = dim.index(),
          old = dim.bisect(dim.range),
          range = dim.bisect(query),
          lo1 = range[0],
          hi1 = range[1],
          lo0 = old[0],
          hi0 = old[1],
          one = dim.one,
          i, j, k;
  
      // Fast incremental update based on previous lo index.
      if (lo1 < lo0) {
        for (i = lo1, j = Math.min(lo0, hi1); i < j; ++i) {
          k = index[i];
          curr[k] ^= one;
          add.push(k);
        }
      } else if (lo1 > lo0) {
        for (i = lo0, j = Math.min(lo1, hi0); i < j; ++i) {
          k = index[i];
          curr[k] ^= one;
          rem.push(k);
        }
      }
  
      // Fast incremental update based on previous hi index.
      if (hi1 > hi0) {
        for (i = Math.max(lo1, hi0), j = hi1; i < j; ++i) {
          k = index[i];
          curr[k] ^= one;
          add.push(k);
        }
      } else if (hi1 < hi0) {
        for (i = Math.max(lo0, hi1), j = hi0; i < j; ++i) {
          k = index[i];
          curr[k] ^= one;
          rem.push(k);
        }
      }
  
      dim.range = query.slice();
    };
  
    /**
     * Selectively filters tuples by resolving against a filter bitmap.
     * Useful for processing the output of a cross-filter transform.
     * @constructor
     * @param {object} params - The parameters for this operator.
     * @param {object} params.ignore - A bit mask indicating which filters to ignore.
     * @param {object} params.filter - The per-tuple filter bitmaps. Typically this
     *   parameter value is a reference to a {@link CrossFilter} transform.
     */
    function ResolveFilter(params) {
      Transform.call(this, null, params);
    }
  
    ResolveFilter.Definition = {
      "type": "ResolveFilter",
      "metadata": {},
      "params": [
        { "name": "ignore", "type": "number", "required": true,
          "description": "A bit mask indicating which filters to ignore." },
        { "name": "filter", "type": "object", "required": true,
          "description": "Per-tuple filter bitmaps from a CrossFilter transform." }
      ]
    };
  
    var prototype$1l = inherits(ResolveFilter, Transform);
  
    prototype$1l.transform = function(_, pulse) {
      var ignore = ~(_.ignore || 0), // bit mask where zeros -> dims to ignore
          bitmap = _.filter,
          mask = bitmap.mask;
  
      // exit early if no relevant filter changes
      if ((mask & ignore) === 0) return pulse.StopPropagation;
  
      var output = pulse.fork(pulse.ALL),
          data = bitmap.data(),
          curr = bitmap.curr(),
          prev = bitmap.prev(),
          pass = function(k) {
            return !(curr[k] & ignore) ? data[k] : null;
          };
  
      // propagate all mod tuples that pass the filter
      output.filter(output.MOD, pass);
  
      // determine add & rem tuples via filter functions
      // for efficiency, we do *not* populate new arrays,
      // instead we add filter functions applied downstream
  
      if (!(mask & (mask-1))) { // only one filter changed
        output.filter(output.ADD, pass);
        output.filter(output.REM, function(k) {
          return (curr[k] & ignore) === mask ? data[k] : null;
        });
  
      } else { // multiple filters changed
        output.filter(output.ADD, function(k) {
          var c = curr[k] & ignore,
              f = !c && (c ^ (prev[k] & ignore));
          return f ? data[k] : null;
        });
        output.filter(output.REM, function(k) {
          var c = curr[k] & ignore,
              f = c && !(c ^ (c ^ (prev[k] & ignore)));
          return f ? data[k] : null;
        });
      }
  
      // add filter to source data in case of reflow...
      return output.filter(output.SOURCE, function(t) { return pass(t._index); });
    };
  
  
  
    var xf = /*#__PURE__*/Object.freeze({
      crossfilter: CrossFilter,
      resolvefilter: ResolveFilter
    });
  
    var version = "5.4.1";
  
    var Default = 'default';
  
    function cursor(view) {
      var cursor = view._signals.cursor;
  
      // add cursor signal to dataflow, if needed
      if (!cursor) {
        view._signals.cursor = (cursor = view.add({user: Default, item: null}));
      }
  
      // evaluate cursor on each mousemove event
      view.on(view.events('view', 'mousemove'), cursor,
        function(_, event) {
          var value = cursor.value,
              user = value ? (isString(value) ? value : value.user) : Default,
              item = event.item && event.item.cursor || null;
  
          return (value && user === value.user && item == value.item) ? value
            : {user: user, item: item};
        }
      );
  
      // when cursor signal updates, set visible cursor
      view.add(null, function(_) {
        var user = _.cursor,
            item = this.value;
  
        if (!isString(user)) {
          item = user.item;
          user = user.user;
        }
  
        setCursor(user && user !== Default ? user : (item || user));
  
        return item;
      }, {cursor: cursor});
    }
  
    function setCursor(cursor) {
      // set cursor on document body
      // this ensures cursor applies even if dragging out of view
      if (typeof document !== 'undefined' && document.body) {
        document.body.style.cursor = cursor;
      }
    }
  
    function dataref(view, name) {
      var data = view._runtime.data;
      if (!data.hasOwnProperty(name)) {
        error('Unrecognized data set: ' + name);
      }
      return data[name];
    }
  
    function data(name) {
      return dataref(this, name).values.value;
    }
  
    function change(name, changes) {
      if (!isChangeSet(changes)) {
        error('Second argument to changes must be a changeset.');
      }
      var dataset = dataref(this, name);
      dataset.modified = true;
      return this.pulse(dataset.input, changes);
    }
  
    function insert(name, _) {
      return change.call(this, name, changeset().insert(_));
    }
  
    function remove(name, _) {
      return change.call(this, name, changeset().remove(_));
    }
  
    function width(view) {
      var padding = view.padding();
      return Math.max(0, view._viewWidth + padding.left + padding.right);
    }
  
    function height(view) {
      var padding = view.padding();
      return Math.max(0, view._viewHeight + padding.top + padding.bottom);
    }
  
    function offset$1(view) {
      var padding = view.padding(),
          origin = view._origin;
      return [
        padding.left + origin[0],
        padding.top + origin[1]
      ];
    }
  
    function resizeRenderer(view) {
      var origin = offset$1(view),
          w = width(view),
          h = height(view);
  
      view._renderer.background(view._background);
      view._renderer.resize(w, h, origin);
      view._handler.origin(origin);
  
      view._resizeListeners.forEach(function(handler) {
        try {
          handler(w, h);
        } catch (error) {
          view.error(error);
        }
      });
    }
  
    /**
     * Extend an event with additional view-specific methods.
     * Adds a new property ('vega') to an event that provides a number
     * of methods for querying information about the current interaction.
     * The vega object provides the following methods:
     *   view - Returns the backing View instance.
     *   item - Returns the currently active scenegraph item (if any).
     *   group - Returns the currently active scenegraph group (if any).
     *     This method accepts a single string-typed argument indicating the name
     *     of the desired parent group. The scenegraph will be traversed from
     *     the item up towards the root to search for a matching group. If no
     *     argument is provided the enclosing group for the active item is
     *     returned, unless the item it itself a group, in which case it is
     *     returned directly.
     *   xy - Returns a two-element array containing the x and y coordinates for
     *     mouse or touch events. For touch events, this is based on the first
     *     elements in the changedTouches array. This method accepts a single
     *     argument: either an item instance or mark name that should serve as
     *     the reference coordinate system. If no argument is provided the
     *     top-level view coordinate system is assumed.
     *   x - Returns the current x-coordinate, accepts the same arguments as xy.
     *   y - Returns the current y-coordinate, accepts the same arguments as xy.
     * @param {Event} event - The input event to extend.
     * @param {Item} item - The currently active scenegraph item (if any).
     * @return {Event} - The extended input event.
     */
    function eventExtend(view, event, item) {
      var r  = view._renderer,
          el = r && r.canvas(),
          p, e, translate;
  
      if (el) {
        translate = offset$1(view);
        e = event.changedTouches ? event.changedTouches[0] : event;
        p = point(e, el);
        p[0] -= translate[0];
        p[1] -= translate[1];
      }
  
      event.dataflow = view;
      event.item = item;
      event.vega = extension(view, item, p);
      return event;
    }
  
    function extension(view, item, point) {
      var itemGroup = item
        ? item.mark.marktype === 'group' ? item : item.mark.group
        : null;
  
      function group(name) {
        var g = itemGroup, i;
        if (name) for (i = item; i; i = i.mark.group) {
          if (i.mark.name === name) { g = i; break; }
        }
        return g && g.mark && g.mark.interactive ? g : {};
      }
  
      function xy(item) {
        if (!item) return point;
        if (isString(item)) item = group(item);
  
        var p = point.slice();
        while (item) {
          p[0] -= item.x || 0;
          p[1] -= item.y || 0;
          item = item.mark && item.mark.group;
        }
        return p;
      }
  
      return {
        view:  constant(view),
        item:  constant(item || {}),
        group: group,
        xy:    xy,
        x:     function(item) { return xy(item)[0]; },
        y:     function(item) { return xy(item)[1]; }
      };
    }
  
    var VIEW = 'view',
        TIMER = 'timer',
        WINDOW = 'window',
        NO_TRAP = {trap: false};
  
    /**
     * Initialize event handling configuration.
     * @param {object} config - The configuration settings.
     * @return {object}
     */
    function initializeEventConfig(config) {
      config = extend({}, config);
  
      var def = config.defaults;
      if (def) {
        if (isArray(def.prevent)) {
          def.prevent = toSet(def.prevent);
        }
        if (isArray(def.allow)) {
          def.allow = toSet(def.allow);
        }
      }
  
      return config;
    }
  
    function prevent(view, type) {
      var def = view._eventConfig.defaults,
          prevent = def && def.prevent,
          allow = def && def.allow;
  
      return prevent === false || allow === true ? false
        : prevent === true || allow === false ? true
        : prevent ? prevent[type]
        : allow ? !allow[type]
        : view.preventDefault();
    }
  
    /**
     * Create a new event stream from an event source.
     * @param {object} source - The event source to monitor.
     * @param {string} type - The event type.
     * @param {function(object): boolean} [filter] - Event filter function.
     * @return {EventStream}
     */
    function events$1(source, type, filter) {
      var view = this,
          s = new EventStream(filter),
          send = function(e, item) {
            view.runAsync(null, () => {
              if (source === VIEW && prevent(view, type)) {
                e.preventDefault();
              }
              s.receive(eventExtend(view, e, item));
            });
          },
          sources;
  
      if (source === TIMER) {
        view.timer(send, type);
      }
  
      else if (source === VIEW) {
        // send traps errors, so use {trap: false} option
        view.addEventListener(type, send, NO_TRAP);
      }
  
      else {
        if (source === WINDOW) {
          if (typeof window !== 'undefined') sources = [window];
        } else if (typeof document !== 'undefined') {
          sources = document.querySelectorAll(source);
        }
  
        if (!sources) {
          view.warn('Can not resolve event source: ' + source);
        } else {
          for (var i=0, n=sources.length; i<n; ++i) {
            sources[i].addEventListener(type, send);
          }
  
          view._eventListeners.push({
            type:    type,
            sources: sources,
            handler: send
          });
        }
      }
  
      return s;
    }
  
    function itemFilter(event) {
      return event.item;
    }
  
    function markTarget(event) {
      // grab upstream collector feeding the mark operator
      var source = event.item.mark.source;
      return source.source || source;
    }
  
    function invoke(name) {
      return function(_, event) {
        return event.vega.view()
          .changeset()
          .encode(event.item, name);
      };
    }
  
    function hover(hoverSet, leaveSet) {
      hoverSet = [hoverSet || 'hover'];
      leaveSet = [leaveSet || 'update', hoverSet[0]];
  
      // invoke hover set upon mouseover
      this.on(
        this.events('view', 'mouseover', itemFilter),
        markTarget,
        invoke(hoverSet)
      );
  
      // invoke leave set upon mouseout
      this.on(
        this.events('view', 'mouseout', itemFilter),
        markTarget,
        invoke(leaveSet)
      );
  
      return this;
    }
  
    /**
     * Finalize a View instance that is being removed.
     * Cancel any running timers.
     * Remove all external event listeners.
     * Remove any currently displayed tooltip.
     */
    function finalize() {
      var tooltip = this._tooltip,
          timers = this._timers,
          listeners = this._eventListeners,
          n, m, e;
  
      n = timers.length;
      while (--n >= 0) {
        timers[n].stop();
      }
  
      n = listeners.length;
      while (--n >= 0) {
        e = listeners[n];
        m = e.sources.length;
        while (--m >= 0) {
          e.sources[m].removeEventListener(e.type, e.handler);
        }
      }
  
      if (tooltip) {
        tooltip.call(this, this._handler, null, null, null);
      }
  
      return this;
    }
  
    function element$1(tag, attr, text) {
      var el = document.createElement(tag);
      for (var key in attr) el.setAttribute(key, attr[key]);
      if (text != null) el.textContent = text;
      return el;
    }
  
    var BindClass = 'vega-bind',
        NameClass = 'vega-bind-name',
        RadioClass = 'vega-bind-radio',
        OptionClass = 'vega-option-';
  
    /**
     * Bind a signal to an external HTML input element. The resulting two-way
     * binding will propagate input changes to signals, and propagate signal
     * changes to the input element state. If this view instance has no parent
     * element, we assume the view is headless and no bindings are created.
     * @param {Element|string} el - The parent DOM element to which the input
     *   element should be appended as a child. If string-valued, this argument
     *   will be treated as a CSS selector. If null or undefined, the parent
     *   element of this view will be used as the element.
     * @param {object} param - The binding parameters which specify the signal
     *   to bind to, the input element type, and type-specific configuration.
     * @return {View} - This view instance.
     */
    function bind$1(view, el, binding) {
      if (!el) return;
  
      var param = binding.param,
          bind = binding.state;
  
      if (!bind) {
        bind = binding.state = {
          elements: null,
          active: false,
          set: null,
          update: function(value) {
            if (value !== view.signal(param.signal)) {
              view.runAsync(null, function() {
                bind.source = true;
                view.signal(param.signal, value);
              });
            }
          }
        };
        if (param.debounce) {
          bind.update = debounce(param.debounce, bind.update);
        }
      }
  
      generate(bind, el, param, view.signal(param.signal));
  
      if (!bind.active) {
        view.on(view._signals[param.signal], null, function() {
          bind.source
            ? (bind.source = false)
            : bind.set(view.signal(param.signal));
        });
        bind.active = true;
      }
  
      return bind;
    }
  
    /**
     * Generate an HTML input form element and bind it to a signal.
     */
    function generate(bind, el, param, value) {
      var div = element$1('div', {'class': BindClass});
  
      div.appendChild(element$1('span',
        {'class': NameClass},
        (param.name || param.signal)
      ));
  
      el.appendChild(div);
  
      var input = form;
      switch (param.input) {
        case 'checkbox': input = checkbox; break;
        case 'select':   input = select; break;
        case 'radio':    input = radio; break;
        case 'range':    input = range; break;
      }
  
      input(bind, div, param, value);
    }
  
    /**
     * Generates an arbitrary input form element.
     * The input type is controlled via user-provided parameters.
     */
    function form(bind, el, param, value) {
      var node = element$1('input');
  
      for (var key in param) {
        if (key !== 'signal' && key !== 'element') {
          node.setAttribute(key === 'input' ? 'type' : key, param[key]);
        }
      }
      node.setAttribute('name', param.signal);
      node.value = value;
  
      el.appendChild(node);
  
      node.addEventListener('input', function() {
        bind.update(node.value);
      });
  
      bind.elements = [node];
      bind.set = function(value) { node.value = value; };
    }
  
    /**
     * Generates a checkbox input element.
     */
    function checkbox(bind, el, param, value) {
      var attr = {type: 'checkbox', name: param.signal};
      if (value) attr.checked = true;
      var node = element$1('input', attr);
  
      el.appendChild(node);
  
      node.addEventListener('change', function() {
        bind.update(node.checked);
      });
  
      bind.elements = [node];
      bind.set = function(value) { node.checked = !!value || null; };
    }
  
    /**
     * Generates a selection list input element.
     */
    function select(bind, el, param, value) {
      var node = element$1('select', {name: param.signal});
  
      param.options.forEach(function(option) {
        var attr = {value: option};
        if (valuesEqual(option, value)) attr.selected = true;
        node.appendChild(element$1('option', attr, option+''));
      });
  
      el.appendChild(node);
  
      node.addEventListener('change', function() {
        bind.update(param.options[node.selectedIndex]);
      });
  
      bind.elements = [node];
      bind.set = function(value) {
        for (var i=0, n=param.options.length; i<n; ++i) {
          if (valuesEqual(param.options[i], value)) {
            node.selectedIndex = i; return;
          }
        }
      };
    }
  
    /**
     * Generates a radio button group.
     */
    function radio(bind, el, param, value) {
      var group = element$1('span', {'class': RadioClass});
  
      el.appendChild(group);
  
      bind.elements = param.options.map(function(option) {
        var id = OptionClass + param.signal + '-' + option;
  
        var attr = {
          id:    id,
          type:  'radio',
          name:  param.signal,
          value: option
        };
        if (valuesEqual(option, value)) attr.checked = true;
  
        var input = element$1('input', attr);
  
        input.addEventListener('change', function() {
          bind.update(option);
        });
  
        group.appendChild(input);
        group.appendChild(element$1('label', {'for': id}, option+''));
  
        return input;
      });
  
      bind.set = function(value) {
        var nodes = bind.elements,
            i = 0,
            n = nodes.length;
        for (; i<n; ++i) {
          if (valuesEqual(nodes[i].value, value)) nodes[i].checked = true;
        }
      };
    }
  
    /**
     * Generates a slider input element.
     */
    function range(bind, el, param, value) {
      value = value !== undefined ? value : ((+param.max) + (+param.min)) / 2;
  
      var min = param.min || Math.min(0, +value) || 0,
          max = param.max || Math.max(100, +value) || 100,
          step = param.step || d3Array.tickStep(min, max, 100);
  
      var node = element$1('input', {
        type:  'range',
        name:  param.signal,
        min:   min,
        max:   max,
        step:  step
      });
      node.value = value;
  
      var label = element$1('label', {}, +value);
  
      el.appendChild(node);
      el.appendChild(label);
  
      function update() {
        label.textContent = node.value;
        bind.update(+node.value);
      }
  
      // subscribe to both input and change
      node.addEventListener('input', update);
      node.addEventListener('change', update);
  
      bind.elements = [node];
      bind.set = function(value) {
        node.value = value;
        label.textContent = value;
      };
    }
  
    function valuesEqual(a, b) {
      return a === b || (a+'' === b+'');
    }
  
    function initializeRenderer(view, r, el, constructor, scaleFactor, opt) {
      r = r || new constructor(view.loader());
      return r
        .initialize(el, width(view), height(view), offset$1(view), scaleFactor, opt)
        .background(view._background);
    }
  
    function trap(view, fn) {
      return !fn ? null : function() {
        try {
          fn.apply(this, arguments);
        } catch (error) {
          view.error(error);
        }
      };
    }
  
    function initializeHandler(view, prevHandler, el, constructor) {
      // instantiate scenegraph handler
      var handler = new constructor(view.loader(), trap(view, view.tooltip()))
        .scene(view.scenegraph().root)
        .initialize(el, offset$1(view), view);
  
      // transfer event handlers
      if (prevHandler) {
        prevHandler.handlers().forEach(function(h) {
          handler.on(h.type, h.handler);
        });
      }
  
      return handler;
    }
  
    function initialize$1(el, elBind) {
      var view = this,
          type = view._renderType,
          module = renderModule(type),
          Handler, Renderer;
  
      // containing dom element
      el = view._el = el ? lookup$4(view, el) : null;
  
      // select appropriate renderer & handler
      if (!module) view.error('Unrecognized renderer type: ' + type);
      Handler = module.handler || CanvasHandler;
      Renderer = (el ? module.renderer : module.headless);
  
      // initialize renderer and input handler
      view._renderer = !Renderer ? null
        : initializeRenderer(view, view._renderer, el, Renderer);
      view._handler = initializeHandler(view, view._handler, el, Handler);
      view._redraw = true;
  
      // initialize signal bindings
      if (el) {
        elBind = elBind ? (view._elBind = lookup$4(view, elBind))
          : el.appendChild(element$1('div', {'class': 'vega-bindings'}));
  
        view._bind.forEach(function(_) {
          if (_.param.element) {
            _.element = lookup$4(view, _.param.element);
          }
        });
  
        view._bind.forEach(function(_) {
          bind$1(view, _.element || elBind, _);
        });
      }
  
      return view;
    }
  
    function lookup$4(view, el) {
      if (typeof el === 'string') {
        if (typeof document !== 'undefined') {
          el = document.querySelector(el);
          if (!el) {
            view.error('Signal bind element not found: ' + el);
            return null;
          }
        } else {
          view.error('DOM document instance not found.');
          return null;
        }
      }
      if (el) {
        try {
          el.innerHTML = '';
        } catch (e) {
          el = null;
          view.error(e);
        }
      }
      return el;
    }
  
    /**
     * Render the current scene in a headless fashion.
     * This method is asynchronous, returning a Promise instance.
     * @return {Promise} - A Promise that resolves to a renderer.
     */
    async function renderHeadless(view, type, scaleFactor, opt) {
      const module = renderModule(type),
            ctr = module && module.headless;
  
      if (!ctr) error('Unrecognized renderer type: ' + type);
  
      await view.runAsync();
      return initializeRenderer(view, null, null, ctr, scaleFactor, opt)
        .renderAsync(view._scenegraph.root);
    }
  
    /**
     * Produce an image URL for the visualization. Depending on the type
     * parameter, the generated URL contains data for either a PNG or SVG image.
     * The URL can be used (for example) to download images of the visualization.
     * This method is asynchronous, returning a Promise instance.
     * @param {string} type - The image type. One of 'svg', 'png' or 'canvas'.
     *   The 'canvas' and 'png' types are synonyms for a PNG image.
     * @return {Promise} - A promise that resolves to an image URL.
     */
    async function renderToImageURL(type, scaleFactor) {
      if (type !== RenderType.Canvas && type !== RenderType.SVG && type !== RenderType.PNG) {
        error('Unrecognized image type: ' + type);
      }
  
      const r = await renderHeadless(this, type, scaleFactor);
      return type === RenderType.SVG
        ? toBlobURL(r.svg(), 'image/svg+xml')
        : r.canvas().toDataURL('image/png');
    }
  
    function toBlobURL(data, mime) {
      var blob = new Blob([data], {type: mime});
      return window.URL.createObjectURL(blob);
    }
  
    /**
     * Produce a Canvas instance containing a rendered visualization.
     * This method is asynchronous, returning a Promise instance.
     * @return {Promise} - A promise that resolves to a Canvas instance.
     */
    async function renderToCanvas(scaleFactor, opt) {
      const r = await renderHeadless(this, RenderType.Canvas, scaleFactor, opt);
      return r.canvas();
    }
  
    /**
     * Produce a rendered SVG string of the visualization.
     * This method is asynchronous, returning a Promise instance.
     * @return {Promise} - A promise that resolves to an SVG string.
     */
    async function renderToSVG(scaleFactor) {
      const r = await renderHeadless(this, RenderType.SVG, scaleFactor);
      return r.svg();
    }
  
    var RawCode = 'RawCode';
    var Literal = 'Literal';
    var Property = 'Property';
    var Identifier$1 = 'Identifier';
  
    var ArrayExpression = 'ArrayExpression';
    var BinaryExpression = 'BinaryExpression';
    var CallExpression = 'CallExpression';
    var ConditionalExpression = 'ConditionalExpression';
    var LogicalExpression = 'LogicalExpression';
    var MemberExpression = 'MemberExpression';
    var ObjectExpression = 'ObjectExpression';
    var UnaryExpression = 'UnaryExpression';
  
    function ASTNode(type) {
      this.type = type;
    }
  
    ASTNode.prototype.visit = function(visitor) {
      var node = this, c, i, n;
  
      if (visitor(node)) return 1;
  
      for (c=children$1(node), i=0, n=c.length; i<n; ++i) {
        if (c[i].visit(visitor)) return 1;
      }
    };
  
    function children$1(node) {
      switch (node.type) {
        case ArrayExpression:
          return node.elements;
        case BinaryExpression:
        case LogicalExpression:
          return [node.left, node.right];
        case CallExpression:
          var args = node.arguments.slice();
          args.unshift(node.callee);
          return args;
        case ConditionalExpression:
          return [node.test, node.consequent, node.alternate];
        case MemberExpression:
          return [node.object, node.property];
        case ObjectExpression:
          return node.properties;
        case Property:
          return [node.key, node.value];
        case UnaryExpression:
          return [node.argument];
        case Identifier$1:
        case Literal:
        case RawCode:
        default:
          return [];
      }
    }
  
    /*
      The following expression parser is based on Esprima (http://esprima.org/).
      Original header comment and license for Esprima is included here:
  
      Copyright (C) 2013 Ariya Hidayat <ariya.hidayat@gmail.com>
      Copyright (C) 2013 Thaddee Tyl <thaddee.tyl@gmail.com>
      Copyright (C) 2013 Mathias Bynens <mathias@qiwi.be>
      Copyright (C) 2012 Ariya Hidayat <ariya.hidayat@gmail.com>
      Copyright (C) 2012 Mathias Bynens <mathias@qiwi.be>
      Copyright (C) 2012 Joost-Wim Boekesteijn <joost-wim@boekesteijn.nl>
      Copyright (C) 2012 Kris Kowal <kris.kowal@cixar.com>
      Copyright (C) 2012 Yusuke Suzuki <utatane.tea@gmail.com>
      Copyright (C) 2012 Arpad Borsos <arpad.borsos@googlemail.com>
      Copyright (C) 2011 Ariya Hidayat <ariya.hidayat@gmail.com>
  
      Redistribution and use in source and binary forms, with or without
      modification, are permitted provided that the following conditions are met:
  
        * Redistributions of source code must retain the above copyright
          notice, this list of conditions and the following disclaimer.
        * Redistributions in binary form must reproduce the above copyright
          notice, this list of conditions and the following disclaimer in the
          documentation and/or other materials provided with the distribution.
  
      THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
      AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
      IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
      ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
      DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
      (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
      LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
      ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
      (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
      THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
    */
  
    var TokenName,
        source$1,
        index,
        length,
        lookahead;
  
    var TokenBooleanLiteral = 1,
        TokenEOF = 2,
        TokenIdentifier = 3,
        TokenKeyword = 4,
        TokenNullLiteral = 5,
        TokenNumericLiteral = 6,
        TokenPunctuator = 7,
        TokenStringLiteral = 8,
        TokenRegularExpression = 9;
  
    TokenName = {};
    TokenName[TokenBooleanLiteral] = 'Boolean';
    TokenName[TokenEOF] = '<end>';
    TokenName[TokenIdentifier] = 'Identifier';
    TokenName[TokenKeyword] = 'Keyword';
    TokenName[TokenNullLiteral] = 'Null';
    TokenName[TokenNumericLiteral] = 'Numeric';
    TokenName[TokenPunctuator] = 'Punctuator';
    TokenName[TokenStringLiteral] = 'String';
    TokenName[TokenRegularExpression] = 'RegularExpression';
  
    var SyntaxArrayExpression = 'ArrayExpression',
        SyntaxBinaryExpression = 'BinaryExpression',
        SyntaxCallExpression = 'CallExpression',
        SyntaxConditionalExpression = 'ConditionalExpression',
        SyntaxIdentifier = 'Identifier',
        SyntaxLiteral = 'Literal',
        SyntaxLogicalExpression = 'LogicalExpression',
        SyntaxMemberExpression = 'MemberExpression',
        SyntaxObjectExpression = 'ObjectExpression',
        SyntaxProperty = 'Property',
        SyntaxUnaryExpression = 'UnaryExpression';
  
    // Error messages should be identical to V8.
    var MessageUnexpectedToken = 'Unexpected token %0',
        MessageUnexpectedNumber = 'Unexpected number',
        MessageUnexpectedString = 'Unexpected string',
        MessageUnexpectedIdentifier = 'Unexpected identifier',
        MessageUnexpectedReserved = 'Unexpected reserved word',
        MessageUnexpectedEOS = 'Unexpected end of input',
        MessageInvalidRegExp = 'Invalid regular expression',
        MessageUnterminatedRegExp = 'Invalid regular expression: missing /',
        MessageStrictOctalLiteral = 'Octal literals are not allowed in strict mode.',
        MessageStrictDuplicateProperty = 'Duplicate data property in object literal not allowed in strict mode';
  
    var ILLEGAL = 'ILLEGAL',
        DISABLED = 'Disabled.';
  
    // See also tools/generate-unicode-regex.py.
      var RegexNonAsciiIdentifierStart = new RegExp("[\\xAA\\xB5\\xBA\\xC0-\\xD6\\xD8-\\xF6\\xF8-\\u02C1\\u02C6-\\u02D1\\u02E0-\\u02E4\\u02EC\\u02EE\\u0370-\\u0374\\u0376\\u0377\\u037A-\\u037D\\u037F\\u0386\\u0388-\\u038A\\u038C\\u038E-\\u03A1\\u03A3-\\u03F5\\u03F7-\\u0481\\u048A-\\u052F\\u0531-\\u0556\\u0559\\u0561-\\u0587\\u05D0-\\u05EA\\u05F0-\\u05F2\\u0620-\\u064A\\u066E\\u066F\\u0671-\\u06D3\\u06D5\\u06E5\\u06E6\\u06EE\\u06EF\\u06FA-\\u06FC\\u06FF\\u0710\\u0712-\\u072F\\u074D-\\u07A5\\u07B1\\u07CA-\\u07EA\\u07F4\\u07F5\\u07FA\\u0800-\\u0815\\u081A\\u0824\\u0828\\u0840-\\u0858\\u08A0-\\u08B2\\u0904-\\u0939\\u093D\\u0950\\u0958-\\u0961\\u0971-\\u0980\\u0985-\\u098C\\u098F\\u0990\\u0993-\\u09A8\\u09AA-\\u09B0\\u09B2\\u09B6-\\u09B9\\u09BD\\u09CE\\u09DC\\u09DD\\u09DF-\\u09E1\\u09F0\\u09F1\\u0A05-\\u0A0A\\u0A0F\\u0A10\\u0A13-\\u0A28\\u0A2A-\\u0A30\\u0A32\\u0A33\\u0A35\\u0A36\\u0A38\\u0A39\\u0A59-\\u0A5C\\u0A5E\\u0A72-\\u0A74\\u0A85-\\u0A8D\\u0A8F-\\u0A91\\u0A93-\\u0AA8\\u0AAA-\\u0AB0\\u0AB2\\u0AB3\\u0AB5-\\u0AB9\\u0ABD\\u0AD0\\u0AE0\\u0AE1\\u0B05-\\u0B0C\\u0B0F\\u0B10\\u0B13-\\u0B28\\u0B2A-\\u0B30\\u0B32\\u0B33\\u0B35-\\u0B39\\u0B3D\\u0B5C\\u0B5D\\u0B5F-\\u0B61\\u0B71\\u0B83\\u0B85-\\u0B8A\\u0B8E-\\u0B90\\u0B92-\\u0B95\\u0B99\\u0B9A\\u0B9C\\u0B9E\\u0B9F\\u0BA3\\u0BA4\\u0BA8-\\u0BAA\\u0BAE-\\u0BB9\\u0BD0\\u0C05-\\u0C0C\\u0C0E-\\u0C10\\u0C12-\\u0C28\\u0C2A-\\u0C39\\u0C3D\\u0C58\\u0C59\\u0C60\\u0C61\\u0C85-\\u0C8C\\u0C8E-\\u0C90\\u0C92-\\u0CA8\\u0CAA-\\u0CB3\\u0CB5-\\u0CB9\\u0CBD\\u0CDE\\u0CE0\\u0CE1\\u0CF1\\u0CF2\\u0D05-\\u0D0C\\u0D0E-\\u0D10\\u0D12-\\u0D3A\\u0D3D\\u0D4E\\u0D60\\u0D61\\u0D7A-\\u0D7F\\u0D85-\\u0D96\\u0D9A-\\u0DB1\\u0DB3-\\u0DBB\\u0DBD\\u0DC0-\\u0DC6\\u0E01-\\u0E30\\u0E32\\u0E33\\u0E40-\\u0E46\\u0E81\\u0E82\\u0E84\\u0E87\\u0E88\\u0E8A\\u0E8D\\u0E94-\\u0E97\\u0E99-\\u0E9F\\u0EA1-\\u0EA3\\u0EA5\\u0EA7\\u0EAA\\u0EAB\\u0EAD-\\u0EB0\\u0EB2\\u0EB3\\u0EBD\\u0EC0-\\u0EC4\\u0EC6\\u0EDC-\\u0EDF\\u0F00\\u0F40-\\u0F47\\u0F49-\\u0F6C\\u0F88-\\u0F8C\\u1000-\\u102A\\u103F\\u1050-\\u1055\\u105A-\\u105D\\u1061\\u1065\\u1066\\u106E-\\u1070\\u1075-\\u1081\\u108E\\u10A0-\\u10C5\\u10C7\\u10CD\\u10D0-\\u10FA\\u10FC-\\u1248\\u124A-\\u124D\\u1250-\\u1256\\u1258\\u125A-\\u125D\\u1260-\\u1288\\u128A-\\u128D\\u1290-\\u12B0\\u12B2-\\u12B5\\u12B8-\\u12BE\\u12C0\\u12C2-\\u12C5\\u12C8-\\u12D6\\u12D8-\\u1310\\u1312-\\u1315\\u1318-\\u135A\\u1380-\\u138F\\u13A0-\\u13F4\\u1401-\\u166C\\u166F-\\u167F\\u1681-\\u169A\\u16A0-\\u16EA\\u16EE-\\u16F8\\u1700-\\u170C\\u170E-\\u1711\\u1720-\\u1731\\u1740-\\u1751\\u1760-\\u176C\\u176E-\\u1770\\u1780-\\u17B3\\u17D7\\u17DC\\u1820-\\u1877\\u1880-\\u18A8\\u18AA\\u18B0-\\u18F5\\u1900-\\u191E\\u1950-\\u196D\\u1970-\\u1974\\u1980-\\u19AB\\u19C1-\\u19C7\\u1A00-\\u1A16\\u1A20-\\u1A54\\u1AA7\\u1B05-\\u1B33\\u1B45-\\u1B4B\\u1B83-\\u1BA0\\u1BAE\\u1BAF\\u1BBA-\\u1BE5\\u1C00-\\u1C23\\u1C4D-\\u1C4F\\u1C5A-\\u1C7D\\u1CE9-\\u1CEC\\u1CEE-\\u1CF1\\u1CF5\\u1CF6\\u1D00-\\u1DBF\\u1E00-\\u1F15\\u1F18-\\u1F1D\\u1F20-\\u1F45\\u1F48-\\u1F4D\\u1F50-\\u1F57\\u1F59\\u1F5B\\u1F5D\\u1F5F-\\u1F7D\\u1F80-\\u1FB4\\u1FB6-\\u1FBC\\u1FBE\\u1FC2-\\u1FC4\\u1FC6-\\u1FCC\\u1FD0-\\u1FD3\\u1FD6-\\u1FDB\\u1FE0-\\u1FEC\\u1FF2-\\u1FF4\\u1FF6-\\u1FFC\\u2071\\u207F\\u2090-\\u209C\\u2102\\u2107\\u210A-\\u2113\\u2115\\u2119-\\u211D\\u2124\\u2126\\u2128\\u212A-\\u212D\\u212F-\\u2139\\u213C-\\u213F\\u2145-\\u2149\\u214E\\u2160-\\u2188\\u2C00-\\u2C2E\\u2C30-\\u2C5E\\u2C60-\\u2CE4\\u2CEB-\\u2CEE\\u2CF2\\u2CF3\\u2D00-\\u2D25\\u2D27\\u2D2D\\u2D30-\\u2D67\\u2D6F\\u2D80-\\u2D96\\u2DA0-\\u2DA6\\u2DA8-\\u2DAE\\u2DB0-\\u2DB6\\u2DB8-\\u2DBE\\u2DC0-\\u2DC6\\u2DC8-\\u2DCE\\u2DD0-\\u2DD6\\u2DD8-\\u2DDE\\u2E2F\\u3005-\\u3007\\u3021-\\u3029\\u3031-\\u3035\\u3038-\\u303C\\u3041-\\u3096\\u309D-\\u309F\\u30A1-\\u30FA\\u30FC-\\u30FF\\u3105-\\u312D\\u3131-\\u318E\\u31A0-\\u31BA\\u31F0-\\u31FF\\u3400-\\u4DB5\\u4E00-\\u9FCC\\uA000-\\uA48C\\uA4D0-\\uA4FD\\uA500-\\uA60C\\uA610-\\uA61F\\uA62A\\uA62B\\uA640-\\uA66E\\uA67F-\\uA69D\\uA6A0-\\uA6EF\\uA717-\\uA71F\\uA722-\\uA788\\uA78B-\\uA78E\\uA790-\\uA7AD\\uA7B0\\uA7B1\\uA7F7-\\uA801\\uA803-\\uA805\\uA807-\\uA80A\\uA80C-\\uA822\\uA840-\\uA873\\uA882-\\uA8B3\\uA8F2-\\uA8F7\\uA8FB\\uA90A-\\uA925\\uA930-\\uA946\\uA960-\\uA97C\\uA984-\\uA9B2\\uA9CF\\uA9E0-\\uA9E4\\uA9E6-\\uA9EF\\uA9FA-\\uA9FE\\uAA00-\\uAA28\\uAA40-\\uAA42\\uAA44-\\uAA4B\\uAA60-\\uAA76\\uAA7A\\uAA7E-\\uAAAF\\uAAB1\\uAAB5\\uAAB6\\uAAB9-\\uAABD\\uAAC0\\uAAC2\\uAADB-\\uAADD\\uAAE0-\\uAAEA\\uAAF2-\\uAAF4\\uAB01-\\uAB06\\uAB09-\\uAB0E\\uAB11-\\uAB16\\uAB20-\\uAB26\\uAB28-\\uAB2E\\uAB30-\\uAB5A\\uAB5C-\\uAB5F\\uAB64\\uAB65\\uABC0-\\uABE2\\uAC00-\\uD7A3\\uD7B0-\\uD7C6\\uD7CB-\\uD7FB\\uF900-\\uFA6D\\uFA70-\\uFAD9\\uFB00-\\uFB06\\uFB13-\\uFB17\\uFB1D\\uFB1F-\\uFB28\\uFB2A-\\uFB36\\uFB38-\\uFB3C\\uFB3E\\uFB40\\uFB41\\uFB43\\uFB44\\uFB46-\\uFBB1\\uFBD3-\\uFD3D\\uFD50-\\uFD8F\\uFD92-\\uFDC7\\uFDF0-\\uFDFB\\uFE70-\\uFE74\\uFE76-\\uFEFC\\uFF21-\\uFF3A\\uFF41-\\uFF5A\\uFF66-\\uFFBE\\uFFC2-\\uFFC7\\uFFCA-\\uFFCF\\uFFD2-\\uFFD7\\uFFDA-\\uFFDC]"),
          RegexNonAsciiIdentifierPart = new RegExp("[\\xAA\\xB5\\xBA\\xC0-\\xD6\\xD8-\\xF6\\xF8-\\u02C1\\u02C6-\\u02D1\\u02E0-\\u02E4\\u02EC\\u02EE\\u0300-\\u0374\\u0376\\u0377\\u037A-\\u037D\\u037F\\u0386\\u0388-\\u038A\\u038C\\u038E-\\u03A1\\u03A3-\\u03F5\\u03F7-\\u0481\\u0483-\\u0487\\u048A-\\u052F\\u0531-\\u0556\\u0559\\u0561-\\u0587\\u0591-\\u05BD\\u05BF\\u05C1\\u05C2\\u05C4\\u05C5\\u05C7\\u05D0-\\u05EA\\u05F0-\\u05F2\\u0610-\\u061A\\u0620-\\u0669\\u066E-\\u06D3\\u06D5-\\u06DC\\u06DF-\\u06E8\\u06EA-\\u06FC\\u06FF\\u0710-\\u074A\\u074D-\\u07B1\\u07C0-\\u07F5\\u07FA\\u0800-\\u082D\\u0840-\\u085B\\u08A0-\\u08B2\\u08E4-\\u0963\\u0966-\\u096F\\u0971-\\u0983\\u0985-\\u098C\\u098F\\u0990\\u0993-\\u09A8\\u09AA-\\u09B0\\u09B2\\u09B6-\\u09B9\\u09BC-\\u09C4\\u09C7\\u09C8\\u09CB-\\u09CE\\u09D7\\u09DC\\u09DD\\u09DF-\\u09E3\\u09E6-\\u09F1\\u0A01-\\u0A03\\u0A05-\\u0A0A\\u0A0F\\u0A10\\u0A13-\\u0A28\\u0A2A-\\u0A30\\u0A32\\u0A33\\u0A35\\u0A36\\u0A38\\u0A39\\u0A3C\\u0A3E-\\u0A42\\u0A47\\u0A48\\u0A4B-\\u0A4D\\u0A51\\u0A59-\\u0A5C\\u0A5E\\u0A66-\\u0A75\\u0A81-\\u0A83\\u0A85-\\u0A8D\\u0A8F-\\u0A91\\u0A93-\\u0AA8\\u0AAA-\\u0AB0\\u0AB2\\u0AB3\\u0AB5-\\u0AB9\\u0ABC-\\u0AC5\\u0AC7-\\u0AC9\\u0ACB-\\u0ACD\\u0AD0\\u0AE0-\\u0AE3\\u0AE6-\\u0AEF\\u0B01-\\u0B03\\u0B05-\\u0B0C\\u0B0F\\u0B10\\u0B13-\\u0B28\\u0B2A-\\u0B30\\u0B32\\u0B33\\u0B35-\\u0B39\\u0B3C-\\u0B44\\u0B47\\u0B48\\u0B4B-\\u0B4D\\u0B56\\u0B57\\u0B5C\\u0B5D\\u0B5F-\\u0B63\\u0B66-\\u0B6F\\u0B71\\u0B82\\u0B83\\u0B85-\\u0B8A\\u0B8E-\\u0B90\\u0B92-\\u0B95\\u0B99\\u0B9A\\u0B9C\\u0B9E\\u0B9F\\u0BA3\\u0BA4\\u0BA8-\\u0BAA\\u0BAE-\\u0BB9\\u0BBE-\\u0BC2\\u0BC6-\\u0BC8\\u0BCA-\\u0BCD\\u0BD0\\u0BD7\\u0BE6-\\u0BEF\\u0C00-\\u0C03\\u0C05-\\u0C0C\\u0C0E-\\u0C10\\u0C12-\\u0C28\\u0C2A-\\u0C39\\u0C3D-\\u0C44\\u0C46-\\u0C48\\u0C4A-\\u0C4D\\u0C55\\u0C56\\u0C58\\u0C59\\u0C60-\\u0C63\\u0C66-\\u0C6F\\u0C81-\\u0C83\\u0C85-\\u0C8C\\u0C8E-\\u0C90\\u0C92-\\u0CA8\\u0CAA-\\u0CB3\\u0CB5-\\u0CB9\\u0CBC-\\u0CC4\\u0CC6-\\u0CC8\\u0CCA-\\u0CCD\\u0CD5\\u0CD6\\u0CDE\\u0CE0-\\u0CE3\\u0CE6-\\u0CEF\\u0CF1\\u0CF2\\u0D01-\\u0D03\\u0D05-\\u0D0C\\u0D0E-\\u0D10\\u0D12-\\u0D3A\\u0D3D-\\u0D44\\u0D46-\\u0D48\\u0D4A-\\u0D4E\\u0D57\\u0D60-\\u0D63\\u0D66-\\u0D6F\\u0D7A-\\u0D7F\\u0D82\\u0D83\\u0D85-\\u0D96\\u0D9A-\\u0DB1\\u0DB3-\\u0DBB\\u0DBD\\u0DC0-\\u0DC6\\u0DCA\\u0DCF-\\u0DD4\\u0DD6\\u0DD8-\\u0DDF\\u0DE6-\\u0DEF\\u0DF2\\u0DF3\\u0E01-\\u0E3A\\u0E40-\\u0E4E\\u0E50-\\u0E59\\u0E81\\u0E82\\u0E84\\u0E87\\u0E88\\u0E8A\\u0E8D\\u0E94-\\u0E97\\u0E99-\\u0E9F\\u0EA1-\\u0EA3\\u0EA5\\u0EA7\\u0EAA\\u0EAB\\u0EAD-\\u0EB9\\u0EBB-\\u0EBD\\u0EC0-\\u0EC4\\u0EC6\\u0EC8-\\u0ECD\\u0ED0-\\u0ED9\\u0EDC-\\u0EDF\\u0F00\\u0F18\\u0F19\\u0F20-\\u0F29\\u0F35\\u0F37\\u0F39\\u0F3E-\\u0F47\\u0F49-\\u0F6C\\u0F71-\\u0F84\\u0F86-\\u0F97\\u0F99-\\u0FBC\\u0FC6\\u1000-\\u1049\\u1050-\\u109D\\u10A0-\\u10C5\\u10C7\\u10CD\\u10D0-\\u10FA\\u10FC-\\u1248\\u124A-\\u124D\\u1250-\\u1256\\u1258\\u125A-\\u125D\\u1260-\\u1288\\u128A-\\u128D\\u1290-\\u12B0\\u12B2-\\u12B5\\u12B8-\\u12BE\\u12C0\\u12C2-\\u12C5\\u12C8-\\u12D6\\u12D8-\\u1310\\u1312-\\u1315\\u1318-\\u135A\\u135D-\\u135F\\u1380-\\u138F\\u13A0-\\u13F4\\u1401-\\u166C\\u166F-\\u167F\\u1681-\\u169A\\u16A0-\\u16EA\\u16EE-\\u16F8\\u1700-\\u170C\\u170E-\\u1714\\u1720-\\u1734\\u1740-\\u1753\\u1760-\\u176C\\u176E-\\u1770\\u1772\\u1773\\u1780-\\u17D3\\u17D7\\u17DC\\u17DD\\u17E0-\\u17E9\\u180B-\\u180D\\u1810-\\u1819\\u1820-\\u1877\\u1880-\\u18AA\\u18B0-\\u18F5\\u1900-\\u191E\\u1920-\\u192B\\u1930-\\u193B\\u1946-\\u196D\\u1970-\\u1974\\u1980-\\u19AB\\u19B0-\\u19C9\\u19D0-\\u19D9\\u1A00-\\u1A1B\\u1A20-\\u1A5E\\u1A60-\\u1A7C\\u1A7F-\\u1A89\\u1A90-\\u1A99\\u1AA7\\u1AB0-\\u1ABD\\u1B00-\\u1B4B\\u1B50-\\u1B59\\u1B6B-\\u1B73\\u1B80-\\u1BF3\\u1C00-\\u1C37\\u1C40-\\u1C49\\u1C4D-\\u1C7D\\u1CD0-\\u1CD2\\u1CD4-\\u1CF6\\u1CF8\\u1CF9\\u1D00-\\u1DF5\\u1DFC-\\u1F15\\u1F18-\\u1F1D\\u1F20-\\u1F45\\u1F48-\\u1F4D\\u1F50-\\u1F57\\u1F59\\u1F5B\\u1F5D\\u1F5F-\\u1F7D\\u1F80-\\u1FB4\\u1FB6-\\u1FBC\\u1FBE\\u1FC2-\\u1FC4\\u1FC6-\\u1FCC\\u1FD0-\\u1FD3\\u1FD6-\\u1FDB\\u1FE0-\\u1FEC\\u1FF2-\\u1FF4\\u1FF6-\\u1FFC\\u200C\\u200D\\u203F\\u2040\\u2054\\u2071\\u207F\\u2090-\\u209C\\u20D0-\\u20DC\\u20E1\\u20E5-\\u20F0\\u2102\\u2107\\u210A-\\u2113\\u2115\\u2119-\\u211D\\u2124\\u2126\\u2128\\u212A-\\u212D\\u212F-\\u2139\\u213C-\\u213F\\u2145-\\u2149\\u214E\\u2160-\\u2188\\u2C00-\\u2C2E\\u2C30-\\u2C5E\\u2C60-\\u2CE4\\u2CEB-\\u2CF3\\u2D00-\\u2D25\\u2D27\\u2D2D\\u2D30-\\u2D67\\u2D6F\\u2D7F-\\u2D96\\u2DA0-\\u2DA6\\u2DA8-\\u2DAE\\u2DB0-\\u2DB6\\u2DB8-\\u2DBE\\u2DC0-\\u2DC6\\u2DC8-\\u2DCE\\u2DD0-\\u2DD6\\u2DD8-\\u2DDE\\u2DE0-\\u2DFF\\u2E2F\\u3005-\\u3007\\u3021-\\u302F\\u3031-\\u3035\\u3038-\\u303C\\u3041-\\u3096\\u3099\\u309A\\u309D-\\u309F\\u30A1-\\u30FA\\u30FC-\\u30FF\\u3105-\\u312D\\u3131-\\u318E\\u31A0-\\u31BA\\u31F0-\\u31FF\\u3400-\\u4DB5\\u4E00-\\u9FCC\\uA000-\\uA48C\\uA4D0-\\uA4FD\\uA500-\\uA60C\\uA610-\\uA62B\\uA640-\\uA66F\\uA674-\\uA67D\\uA67F-\\uA69D\\uA69F-\\uA6F1\\uA717-\\uA71F\\uA722-\\uA788\\uA78B-\\uA78E\\uA790-\\uA7AD\\uA7B0\\uA7B1\\uA7F7-\\uA827\\uA840-\\uA873\\uA880-\\uA8C4\\uA8D0-\\uA8D9\\uA8E0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 
    // Ensure the condition is true, otherwise throw an error.
    // This is only to have a better contract semantic, i.e. another safety net
    // to catch a logic error. The condition shall be fulfilled in normal case.
    // Do NOT use this to enforce a certain condition on any user input.
  
    function assert(condition, message) {
      /* istanbul ignore next */
      if (!condition) {
        throw new Error('ASSERT: ' + message);
      }
    }
  
    function isDecimalDigit(ch) {
      return (ch >= 0x30 && ch <= 0x39); // 0..9
    }
  
    function isHexDigit(ch) {
      return '0123456789abcdefABCDEF'.indexOf(ch) >= 0;
    }
  
    function isOctalDigit(ch) {
      return '01234567'.indexOf(ch) >= 0;
    }
  
    // 7.2 White Space
  
    function isWhiteSpace(ch) {
      return (ch === 0x20) || (ch === 0x09) || (ch === 0x0B) || (ch === 0x0C) || (ch === 0xA0) ||
        (ch >= 0x1680 && [0x1680, 0x180E, 0x2000, 0x2001, 0x2002, 0x2003, 0x2004, 0x2005, 0x2006, 0x2007, 0x2008, 0x2009, 0x200A, 0x202F, 0x205F, 0x3000, 0xFEFF].indexOf(ch) >= 0);
    }
  
    // 7.3 Line Terminators
  
    function isLineTerminator(ch) {
      return (ch === 0x0A) || (ch === 0x0D) || (ch === 0x2028) || (ch === 0x2029);
    }
  
    // 7.6 Identifier Names and Identifiers
  
    function isIdentifierStart(ch) {
      return (ch === 0x24) || (ch === 0x5F) || // $ (dollar) and _ (underscore)
        (ch >= 0x41 && ch <= 0x5A) || // A..Z
        (ch >= 0x61 && ch <= 0x7A) || // a..z
        (ch === 0x5C) || // \ (backslash)
        ((ch >= 0x80) && RegexNonAsciiIdentifierStart.test(String.fromCharCode(ch)));
    }
  
    function isIdentifierPart(ch) {
      return (ch === 0x24) || (ch === 0x5F) || // $ (dollar) and _ (underscore)
        (ch >= 0x41 && ch <= 0x5A) || // A..Z
        (ch >= 0x61 && ch <= 0x7A) || // a..z
        (ch >= 0x30 && ch <= 0x39) || // 0..9
        (ch === 0x5C) || // \ (backslash)
        ((ch >= 0x80) && RegexNonAsciiIdentifierPart.test(String.fromCharCode(ch)));
    }
  
    // 7.6.1.1 Keywords
  
    var keywords = {
      'if':1, 'in':1, 'do':1,
      'var':1, 'for':1, 'new':1, 'try':1, 'let':1,
      'this':1, 'else':1, 'case':1, 'void':1, 'with':1, 'enum':1,
      'while':1, 'break':1, 'catch':1, 'throw':1, 'const':1, 'yield':1, 'class':1, 'super':1,
      'return':1, 'typeof':1, 'delete':1, 'switch':1, 'export':1, 'import':1, 'public':1, 'static':1,
      'default':1, 'finally':1, 'extends':1, 'package':1, 'private':1,
      'function':1, 'continue':1, 'debugger':1,
      'interface':1, 'protected':1,
      'instanceof':1, 'implements':1
    };
  
    function skipComment() {
      var ch;
  
      while (index < length) {
        ch = source$1.charCodeAt(index);
  
        if (isWhiteSpace(ch) || isLineTerminator(ch)) {
          ++index;
        } else {
          break;
        }
      }
    }
  
    function scanHexEscape(prefix) {
      var i, len, ch, code = 0;
  
      len = (prefix === 'u') ? 4 : 2;
      for (i = 0; i < len; ++i) {
        if (index < length && isHexDigit(source$1[index])) {
          ch = source$1[index++];
          code = code * 16 + '0123456789abcdef'.indexOf(ch.toLowerCase());
        } else {
          throwError({}, MessageUnexpectedToken, ILLEGAL);
        }
      }
      return String.fromCharCode(code);
    }
  
    function scanUnicodeCodePointEscape() {
      var ch, code, cu1, cu2;
  
      ch = source$1[index];
      code = 0;
  
      // At least, one hex digit is required.
      if (ch === '}') {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      while (index < length) {
        ch = source$1[index++];
        if (!isHexDigit(ch)) {
          break;
        }
        code = code * 16 + '0123456789abcdef'.indexOf(ch.toLowerCase());
      }
  
      if (code > 0x10FFFF || ch !== '}') {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      // UTF-16 Encoding
      if (code <= 0xFFFF) {
        return String.fromCharCode(code);
      }
      cu1 = ((code - 0x10000) >> 10) + 0xD800;
      cu2 = ((code - 0x10000) & 1023) + 0xDC00;
      return String.fromCharCode(cu1, cu2);
    }
  
    function getEscapedIdentifier() {
      var ch, id;
  
      ch = source$1.charCodeAt(index++);
      id = String.fromCharCode(ch);
  
      // '\u' (U+005C, U+0075) denotes an escaped character.
      if (ch === 0x5C) {
        if (source$1.charCodeAt(index) !== 0x75) {
          throwError({}, MessageUnexpectedToken, ILLEGAL);
        }
        ++index;
        ch = scanHexEscape('u');
        if (!ch || ch === '\\' || !isIdentifierStart(ch.charCodeAt(0))) {
          throwError({}, MessageUnexpectedToken, ILLEGAL);
        }
        id = ch;
      }
  
      while (index < length) {
        ch = source$1.charCodeAt(index);
        if (!isIdentifierPart(ch)) {
          break;
        }
        ++index;
        id += String.fromCharCode(ch);
  
        // '\u' (U+005C, U+0075) denotes an escaped character.
        if (ch === 0x5C) {
          id = id.substr(0, id.length - 1);
          if (source$1.charCodeAt(index) !== 0x75) {
            throwError({}, MessageUnexpectedToken, ILLEGAL);
          }
          ++index;
          ch = scanHexEscape('u');
          if (!ch || ch === '\\' || !isIdentifierPart(ch.charCodeAt(0))) {
            throwError({}, MessageUnexpectedToken, ILLEGAL);
          }
          id += ch;
        }
      }
  
      return id;
    }
  
    function getIdentifier() {
      var start, ch;
  
      start = index++;
      while (index < length) {
        ch = source$1.charCodeAt(index);
        if (ch === 0x5C) {
          // Blackslash (U+005C) marks Unicode escape sequence.
          index = start;
          return getEscapedIdentifier();
        }
        if (isIdentifierPart(ch)) {
          ++index;
        } else {
          break;
        }
      }
  
      return source$1.slice(start, index);
    }
  
    function scanIdentifier() {
      var start, id, type;
  
      start = index;
  
      // Backslash (U+005C) starts an escaped character.
      id = (source$1.charCodeAt(index) === 0x5C) ? getEscapedIdentifier() : getIdentifier();
  
      // There is no keyword or literal with only one character.
      // Thus, it must be an identifier.
      if (id.length === 1) {
        type = TokenIdentifier;
      } else if (keywords.hasOwnProperty(id)) {
        type = TokenKeyword;
      } else if (id === 'null') {
        type = TokenNullLiteral;
      } else if (id === 'true' || id === 'false') {
        type = TokenBooleanLiteral;
      } else {
        type = TokenIdentifier;
      }
  
      return {
        type: type,
        value: id,
        start: start,
        end: index
      };
    }
  
    // 7.7 Punctuators
  
    function scanPunctuator() {
      var start = index,
        code = source$1.charCodeAt(index),
        code2,
        ch1 = source$1[index],
        ch2,
        ch3,
        ch4;
  
      switch (code) {
  
        // Check for most common single-character punctuators.
        case 0x2E: // . dot
        case 0x28: // ( open bracket
        case 0x29: // ) close bracket
        case 0x3B: // ; semicolon
        case 0x2C: // , comma
        case 0x7B: // { open curly brace
        case 0x7D: // } close curly brace
        case 0x5B: // [
        case 0x5D: // ]
        case 0x3A: // :
        case 0x3F: // ?
        case 0x7E: // ~
          ++index;
          return {
            type: TokenPunctuator,
            value: String.fromCharCode(code),
            start: start,
            end: index
          };
  
        default:
          code2 = source$1.charCodeAt(index + 1);
  
          // '=' (U+003D) marks an assignment or comparison operator.
          if (code2 === 0x3D) {
            switch (code) {
              case 0x2B: // +
              case 0x2D: // -
              case 0x2F: // /
              case 0x3C: // <
              case 0x3E: // >
              case 0x5E: // ^
              case 0x7C: // |
              case 0x25: // %
              case 0x26: // &
              case 0x2A: // *
                index += 2;
                return {
                  type: TokenPunctuator,
                  value: String.fromCharCode(code) + String.fromCharCode(code2),
                  start: start,
                  end: index
                };
  
              case 0x21: // !
              case 0x3D: // =
                index += 2;
  
                // !== and ===
                if (source$1.charCodeAt(index) === 0x3D) {
                  ++index;
                }
                return {
                  type: TokenPunctuator,
                  value: source$1.slice(start, index),
                  start: start,
                  end: index
                };
            }
          }
      }
  
      // 4-character punctuator: >>>=
  
      ch4 = source$1.substr(index, 4);
  
      if (ch4 === '>>>=') {
        index += 4;
        return {
          type: TokenPunctuator,
          value: ch4,
          start: start,
          end: index
        };
      }
  
      // 3-character punctuators: === !== >>> <<= >>=
  
      ch3 = ch4.substr(0, 3);
  
      if (ch3 === '>>>' || ch3 === '<<=' || ch3 === '>>=') {
        index += 3;
        return {
          type: TokenPunctuator,
          value: ch3,
          start: start,
          end: index
        };
      }
  
      // Other 2-character punctuators: ++ -- << >> && ||
      ch2 = ch3.substr(0, 2);
  
      if ((ch1 === ch2[1] && ('+-<>&|'.indexOf(ch1) >= 0)) || ch2 === '=>') {
        index += 2;
        return {
          type: TokenPunctuator,
          value: ch2,
          start: start,
          end: index
        };
      }
  
      // 1-character punctuators: < > = ! + - * % & | ^ /
  
      if ('<>=!+-*%&|^/'.indexOf(ch1) >= 0) {
        ++index;
        return {
          type: TokenPunctuator,
          value: ch1,
          start: start,
          end: index
        };
      }
  
      throwError({}, MessageUnexpectedToken, ILLEGAL);
    }
  
    // 7.8.3 Numeric Literals
  
    function scanHexLiteral(start) {
      var number = '';
  
      while (index < length) {
        if (!isHexDigit(source$1[index])) {
          break;
        }
        number += source$1[index++];
      }
  
      if (number.length === 0) {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      if (isIdentifierStart(source$1.charCodeAt(index))) {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      return {
        type: TokenNumericLiteral,
        value: parseInt('0x' + number, 16),
        start: start,
        end: index
      };
    }
  
    function scanOctalLiteral(start) {
      var number = '0' + source$1[index++];
      while (index < length) {
        if (!isOctalDigit(source$1[index])) {
          break;
        }
        number += source$1[index++];
      }
  
      if (isIdentifierStart(source$1.charCodeAt(index)) || isDecimalDigit(source$1.charCodeAt(index))) {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      return {
        type: TokenNumericLiteral,
        value: parseInt(number, 8),
        octal: true,
        start: start,
        end: index
      };
    }
  
    function scanNumericLiteral() {
      var number, start, ch;
  
      ch = source$1[index];
      assert(isDecimalDigit(ch.charCodeAt(0)) || (ch === '.'),
        'Numeric literal must start with a decimal digit or a decimal point');
  
      start = index;
      number = '';
      if (ch !== '.') {
        number = source$1[index++];
        ch = source$1[index];
  
        // Hex number starts with '0x'.
        // Octal number starts with '0'.
        if (number === '0') {
          if (ch === 'x' || ch === 'X') {
            ++index;
            return scanHexLiteral(start);
          }
          if (isOctalDigit(ch)) {
            return scanOctalLiteral(start);
          }
  
          // decimal number starts with '0' such as '09' is illegal.
          if (ch && isDecimalDigit(ch.charCodeAt(0))) {
            throwError({}, MessageUnexpectedToken, ILLEGAL);
          }
        }
  
        while (isDecimalDigit(source$1.charCodeAt(index))) {
          number += source$1[index++];
        }
        ch = source$1[index];
      }
  
      if (ch === '.') {
        number += source$1[index++];
        while (isDecimalDigit(source$1.charCodeAt(index))) {
          number += source$1[index++];
        }
        ch = source$1[index];
      }
  
      if (ch === 'e' || ch === 'E') {
        number += source$1[index++];
  
        ch = source$1[index];
        if (ch === '+' || ch === '-') {
          number += source$1[index++];
        }
        if (isDecimalDigit(source$1.charCodeAt(index))) {
          while (isDecimalDigit(source$1.charCodeAt(index))) {
            number += source$1[index++];
          }
        } else {
          throwError({}, MessageUnexpectedToken, ILLEGAL);
        }
      }
  
      if (isIdentifierStart(source$1.charCodeAt(index))) {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      return {
        type: TokenNumericLiteral,
        value: parseFloat(number),
        start: start,
        end: index
      };
    }
  
    // 7.8.4 String Literals
  
    function scanStringLiteral() {
      var str = '',
        quote, start, ch, code, octal = false;
  
      quote = source$1[index];
      assert((quote === '\'' || quote === '"'),
        'String literal must starts with a quote');
  
      start = index;
      ++index;
  
      while (index < length) {
        ch = source$1[index++];
  
        if (ch === quote) {
          quote = '';
          break;
        } else if (ch === '\\') {
          ch = source$1[index++];
          if (!ch || !isLineTerminator(ch.charCodeAt(0))) {
            switch (ch) {
              case 'u':
              case 'x':
                if (source$1[index] === '{') {
                  ++index;
                  str += scanUnicodeCodePointEscape();
                } else {
                  str += scanHexEscape(ch);
                }
                break;
              case 'n':
                str += '\n';
                break;
              case 'r':
                str += '\r';
                break;
              case 't':
                str += '\t';
                break;
              case 'b':
                str += '\b';
                break;
              case 'f':
                str += '\f';
                break;
              case 'v':
                str += '\x0B';
                break;
  
              default:
                if (isOctalDigit(ch)) {
                  code = '01234567'.indexOf(ch);
  
                  // \0 is not octal escape sequence
                  if (code !== 0) {
                    octal = true;
                  }
  
                  if (index < length && isOctalDigit(source$1[index])) {
                    octal = true;
                    code = code * 8 + '01234567'.indexOf(source$1[index++]);
  
                    // 3 digits are only allowed when string starts
                    // with 0, 1, 2, 3
                    if ('0123'.indexOf(ch) >= 0 &&
                      index < length &&
                      isOctalDigit(source$1[index])) {
                      code = code * 8 + '01234567'.indexOf(source$1[index++]);
                    }
                  }
                  str += String.fromCharCode(code);
                } else {
                  str += ch;
                }
                break;
            }
          } else {
            if (ch === '\r' && source$1[index] === '\n') {
              ++index;
            }
          }
        } else if (isLineTerminator(ch.charCodeAt(0))) {
          break;
        } else {
          str += ch;
        }
      }
  
      if (quote !== '') {
        throwError({}, MessageUnexpectedToken, ILLEGAL);
      }
  
      return {
        type: TokenStringLiteral,
        value: str,
        octal: octal,
        start: start,
        end: index
      };
    }
  
    function testRegExp(pattern, flags) {
      var tmp = pattern;
  
      if (flags.indexOf('u') >= 0) {
        // Replace each astral symbol and every Unicode code point
        // escape sequence with a single ASCII symbol to avoid throwing on
        // regular expressions that are only valid in combination with the
        // `/u` flag.
        // Note: replacing with the ASCII symbol `x` might cause false
        // negatives in unlikely scenarios. For example, `[\u{61}-b]` is a
        // perfectly valid pattern that is equivalent to `[a-b]`, but it
        // would be replaced by `[x-b]` which throws an error.
        tmp = tmp
          .replace(/\\u\{([0-9a-fA-F]+)\}/g, function($0, $1) {
            if (parseInt($1, 16) <= 0x10FFFF) {
              return 'x';
            }
            throwError({}, MessageInvalidRegExp);
          })
          .replace(/[\uD800-\uDBFF][\uDC00-\uDFFF]/g, 'x');
      }
  
      // First, detect invalid regular expressions.
      try {
        new RegExp(tmp);
      } catch (e) {
        throwError({}, MessageInvalidRegExp);
      }
  
      // Return a regular expression object for this pattern-flag pair, or
      // `null` in case the current environment doesn't support the flags it
      // uses.
      try {
        return new RegExp(pattern, flags);
      } catch (exception) {
        return null;
      }
    }
  
    function scanRegExpBody() {
      var ch, str, classMarker, terminated, body;
  
      ch = source$1[index];
      assert(ch === '/', 'Regular expression literal must start with a slash');
      str = source$1[index++];
  
      classMarker = false;
      terminated = false;
      while (index < length) {
        ch = source$1[index++];
        str += ch;
        if (ch === '\\') {
          ch = source$1[index++];
          // ECMA-262 7.8.5
          if (isLineTerminator(ch.charCodeAt(0))) {
            throwError({}, MessageUnterminatedRegExp);
          }
          str += ch;
        } else if (isLineTerminator(ch.charCodeAt(0))) {
          throwError({}, MessageUnterminatedRegExp);
        } else if (classMarker) {
          if (ch === ']') {
            classMarker = false;
          }
        } else {
          if (ch === '/') {
            terminated = true;
            break;
          } else if (ch === '[') {
            classMarker = true;
          }
        }
      }
  
      if (!terminated) {
        throwError({}, MessageUnterminatedRegExp);
      }
  
      // Exclude leading and trailing slash.
      body = str.substr(1, str.length - 2);
      return {
        value: body,
        literal: str
      };
    }
  
    function scanRegExpFlags() {
      var ch, str, flags;
  
      str = '';
      flags = '';
      while (index < length) {
        ch = source$1[index];
        if (!isIdentifierPart(ch.charCodeAt(0))) {
          break;
        }
  
        ++index;
        if (ch === '\\' && index < length) {
          throwError({}, MessageUnexpectedToken, ILLEGAL);
        } else {
          flags += ch;
          str += ch;
        }
      }
  
      if (flags.search(/[^gimuy]/g) >= 0) {
        throwError({}, MessageInvalidRegExp, flags);
      }
  
      return {
        value: flags,
        literal: str
      };
    }
  
    function scanRegExp() {
      var start, body, flags, value;
  
      lookahead = null;
      skipComment();
      start = index;
  
      body = scanRegExpBody();
      flags = scanRegExpFlags();
      value = testRegExp(body.value, flags.value);
  
      return {
        literal: body.literal + flags.literal,
        value: value,
        regex: {
          pattern: body.value,
          flags: flags.value
        },
        start: start,
        end: index
      };
    }
  
    function isIdentifierName(token) {
      return token.type === TokenIdentifier ||
        token.type === TokenKeyword ||
        token.type === TokenBooleanLiteral ||
        token.type === TokenNullLiteral;
    }
  
    function advance() {
      var ch;
  
      skipComment();
  
      if (index >= length) {
        return {
          type: TokenEOF,
          start: index,
          end: index
        };
      }
  
      ch = source$1.charCodeAt(index);
  
      if (isIdentifierStart(ch)) {
        return scanIdentifier();
      }
  
      // Very common: ( and ) and ;
      if (ch === 0x28 || ch === 0x29 || ch === 0x3B) {
        return scanPunctuator();
      }
  
      // String literal starts with single quote (U+0027) or double quote (U+0022).
      if (ch === 0x27 || ch === 0x22) {
        return scanStringLiteral();
      }
  
  
      // Dot (.) U+002E can also start a floating-point number, hence the need
      // to check the next character.
      if (ch === 0x2E) {
        if (isDecimalDigit(source$1.charCodeAt(index + 1))) {
          return scanNumericLiteral();
        }
        return scanPunctuator();
      }
  
      if (isDecimalDigit(ch)) {
        return scanNumericLiteral();
      }
  
      return scanPunctuator();
    }
  
    function lex() {
      var token;
  
      token = lookahead;
      index = token.end;
  
      lookahead = advance();
  
      index = token.end;
  
      return token;
    }
  
    function peek$1() {
      var pos;
  
      pos = index;
  
      lookahead = advance();
      index = pos;
    }
  
    function finishArrayExpression(elements) {
      var node = new ASTNode(SyntaxArrayExpression);
      node.elements = elements;
      return node;
    }
  
    function finishBinaryExpression(operator, left, right) {
      var node = new ASTNode((operator === '||' || operator === '&&') ? SyntaxLogicalExpression : SyntaxBinaryExpression);
      node.operator = operator;
      node.left = left;
      node.right = right;
      return node;
    }
  
    function finishCallExpression(callee, args) {
      var node = new ASTNode(SyntaxCallExpression);
      node.callee = callee;
      node.arguments = args;
      return node;
    }
  
    function finishConditionalExpression(test, consequent, alternate) {
      var node = new ASTNode(SyntaxConditionalExpression);
      node.test = test;
      node.consequent = consequent;
      node.alternate = alternate;
      return node;
    }
  
    function finishIdentifier(name) {
      var node = new ASTNode(SyntaxIdentifier);
      node.name = name;
      return node;
    }
  
    function finishLiteral(token) {
      var node = new ASTNode(SyntaxLiteral);
      node.value = token.value;
      node.raw = source$1.slice(token.start, token.end);
      if (token.regex) {
        if (node.raw === '//') {
          node.raw = '/(?:)/';
        }
        node.regex = token.regex;
      }
      return node;
    }
  
    function finishMemberExpression(accessor, object, property) {
      var node = new ASTNode(SyntaxMemberExpression);
      node.computed = accessor === '[';
      node.object = object;
      node.property = property;
      if (!node.computed) property.member = true;
      return node;
    }
  
    function finishObjectExpression(properties) {
      var node = new ASTNode(SyntaxObjectExpression);
      node.properties = properties;
      return node;
    }
  
    function finishProperty(kind, key, value) {
      var node = new ASTNode(SyntaxProperty);
      node.key = key;
      node.value = value;
      node.kind = kind;
      return node;
    }
  
    function finishUnaryExpression(operator, argument) {
      var node = new ASTNode(SyntaxUnaryExpression);
      node.operator = operator;
      node.argument = argument;
      node.prefix = true;
      return node;
    }
  
    // Throw an exception
  
    function throwError(token, messageFormat) {
      var error,
        args = Array.prototype.slice.call(arguments, 2),
        msg = messageFormat.replace(
          /%(\d)/g,
          function(whole, index) {
            assert(index < args.length, 'Message reference must be in range');
            return args[index];
          }
        );
  
  
      error = new Error(msg);
      error.index = index;
      error.description = msg;
      throw error;
    }
  
    // Throw an exception because of the token.
  
    function throwUnexpected(token) {
      if (token.type === TokenEOF) {
        throwError(token, MessageUnexpectedEOS);
      }
  
      if (token.type === TokenNumericLiteral) {
        throwError(token, MessageUnexpectedNumber);
      }
  
      if (token.type === TokenStringLiteral) {
        throwError(token, MessageUnexpectedString);
      }
  
      if (token.type === TokenIdentifier) {
        throwError(token, MessageUnexpectedIdentifier);
      }
  
      if (token.type === TokenKeyword) {
        throwError(token, MessageUnexpectedReserved);
      }
  
      // BooleanLiteral, NullLiteral, or Punctuator.
      throwError(token, MessageUnexpectedToken, token.value);
    }
  
    // Expect the next token to match the specified punctuator.
    // If not, an exception will be thrown.
  
    function expect(value) {
      var token = lex();
      if (token.type !== TokenPunctuator || token.value !== value) {
        throwUnexpected(token);
      }
    }
  
    // Return true if the next token matches the specified punctuator.
  
    function match(value) {
      return lookahead.type === TokenPunctuator && lookahead.value === value;
    }
  
    // Return true if the next token matches the specified keyword
  
    function matchKeyword(keyword) {
      return lookahead.type === TokenKeyword && lookahead.value === keyword;
    }
  
    // 11.1.4 Array Initialiser
  
    function parseArrayInitialiser() {
      var elements = [];
  
      index = lookahead.start;
      expect('[');
  
      while (!match(']')) {
        if (match(',')) {
          lex();
          elements.push(null);
        } else {
          elements.push(parseConditionalExpression());
  
          if (!match(']')) {
            expect(',');
          }
        }
      }
  
      lex();
  
      return finishArrayExpression(elements);
    }
  
    // 11.1.5 Object Initialiser
  
    function parseObjectPropertyKey() {
      var token;
  
      index = lookahead.start;
      token = lex();
  
      // Note: This function is called only from parseObjectProperty(), where
      // EOF and Punctuator tokens are already filtered out.
  
      if (token.type === TokenStringLiteral || token.type === TokenNumericLiteral) {
        if (token.octal) {
          throwError(token, MessageStrictOctalLiteral);
        }
        return finishLiteral(token);
      }
  
      return finishIdentifier(token.value);
    }
  
    function parseObjectProperty() {
      var token, key, id, value;
  
      index = lookahead.start;
      token = lookahead;
  
      if (token.type === TokenIdentifier) {
        id = parseObjectPropertyKey();
        expect(':');
        value = parseConditionalExpression();
        return finishProperty('init', id, value);
      }
      if (token.type === TokenEOF || token.type === TokenPunctuator) {
        throwUnexpected(token);
      } else {
        key = parseObjectPropertyKey();
        expect(':');
        value = parseConditionalExpression();
        return finishProperty('init', key, value);
      }
    }
  
    function parseObjectInitialiser() {
      var properties = [],
        property, name, key, map = {},
        toString = String;
  
      index = lookahead.start;
      expect('{');
  
      while (!match('}')) {
        property = parseObjectProperty();
  
        if (property.key.type === SyntaxIdentifier) {
          name = property.key.name;
        } else {
          name = toString(property.key.value);
        }
  
        key = '$' + name;
        if (Object.prototype.hasOwnProperty.call(map, key)) {
          throwError({}, MessageStrictDuplicateProperty);
        } else {
          map[key] = true;
        }
  
        properties.push(property);
  
        if (!match('}')) {
          expect(',');
        }
      }
  
      expect('}');
  
      return finishObjectExpression(properties);
    }
  
    // 11.1.6 The Grouping Operator
  
    function parseGroupExpression() {
      var expr;
  
      expect('(');
  
      expr = parseExpression();
  
      expect(')');
  
      return expr;
    }
  
  
    // 11.1 Primary Expressions
  
    var legalKeywords = {
      "if": 1,
      "this": 1
    };
  
    function parsePrimaryExpression() {
      var type, token, expr;
  
      if (match('(')) {
        return parseGroupExpression();
      }
  
      if (match('[')) {
        return parseArrayInitialiser();
      }
  
      if (match('{')) {
        return parseObjectInitialiser();
      }
  
      type = lookahead.type;
      index = lookahead.start;
  
  
      if (type === TokenIdentifier || legalKeywords[lookahead.value]) {
        expr = finishIdentifier(lex().value);
      } else if (type === TokenStringLiteral || type === TokenNumericLiteral) {
        if (lookahead.octal) {
          throwError(lookahead, MessageStrictOctalLiteral);
        }
        expr = finishLiteral(lex());
      } else if (type === TokenKeyword) {
        throw new Error(DISABLED);
      } else if (type === TokenBooleanLiteral) {
        token = lex();
        token.value = (token.value === 'true');
        expr = finishLiteral(token);
      } else if (type === TokenNullLiteral) {
        token = lex();
        token.value = null;
        expr = finishLiteral(token);
      } else if (match('/') || match('/=')) {
        expr = finishLiteral(scanRegExp());
        peek$1();
      } else {
        throwUnexpected(lex());
      }
  
      return expr;
    }
  
    // 11.2 Left-Hand-Side Expressions
  
    function parseArguments() {
      var args = [];
  
      expect('(');
  
      if (!match(')')) {
        while (index < length) {
          args.push(parseConditionalExpression());
          if (match(')')) {
            break;
          }
          expect(',');
        }
      }
  
      expect(')');
  
      return args;
    }
  
    function parseNonComputedProperty() {
      var token;
      index = lookahead.start;
      token = lex();
  
      if (!isIdentifierName(token)) {
        throwUnexpected(token);
      }
  
      return finishIdentifier(token.value);
    }
  
    function parseNonComputedMember() {
      expect('.');
  
      return parseNonComputedProperty();
    }
  
    function parseComputedMember() {
      var expr;
  
      expect('[');
  
      expr = parseExpression();
  
      expect(']');
  
      return expr;
    }
  
    function parseLeftHandSideExpressionAllowCall() {
      var expr, args, property;
  
      expr = parsePrimaryExpression();
  
      for (;;) {
        if (match('.')) {
          property = parseNonComputedMember();
          expr = finishMemberExpression('.', expr, property);
        } else if (match('(')) {
          args = parseArguments();
          expr = finishCallExpression(expr, args);
        } else if (match('[')) {
          property = parseComputedMember();
          expr = finishMemberExpression('[', expr, property);
        } else {
          break;
        }
      }
  
      return expr;
    }
  
    // 11.3 Postfix Expressions
  
    function parsePostfixExpression() {
      var expr = parseLeftHandSideExpressionAllowCall();
  
      if (lookahead.type === TokenPunctuator) {
        if ((match('++') || match('--'))) {
          throw new Error(DISABLED);
        }
      }
  
      return expr;
    }
  
    // 11.4 Unary Operators
  
    function parseUnaryExpression() {
      var token, expr;
  
      if (lookahead.type !== TokenPunctuator && lookahead.type !== TokenKeyword) {
        expr = parsePostfixExpression();
      } else if (match('++') || match('--')) {
        throw new Error(DISABLED);
      } else if (match('+') || match('-') || match('~') || match('!')) {
        token = lex();
        expr = parseUnaryExpression();
        expr = finishUnaryExpression(token.value, expr);
      } else if (matchKeyword('delete') || matchKeyword('void') || matchKeyword('typeof')) {
        throw new Error(DISABLED);
      } else {
        expr = parsePostfixExpression();
      }
  
      return expr;
    }
  
    function binaryPrecedence(token) {
      var prec = 0;
  
      if (token.type !== TokenPunctuator && token.type !== TokenKeyword) {
        return 0;
      }
  
      switch (token.value) {
        case '||':
          prec = 1;
          break;
  
        case '&&':
          prec = 2;
          break;
  
        case '|':
          prec = 3;
          break;
  
        case '^':
          prec = 4;
          break;
  
        case '&':
          prec = 5;
          break;
  
        case '==':
        case '!=':
        case '===':
        case '!==':
          prec = 6;
          break;
  
        case '<':
        case '>':
        case '<=':
        case '>=':
        case 'instanceof':
        case 'in':
          prec = 7;
          break;
  
        case '<<':
        case '>>':
        case '>>>':
          prec = 8;
          break;
  
        case '+':
        case '-':
          prec = 9;
          break;
  
        case '*':
        case '/':
        case '%':
          prec = 11;
          break;
  
        default:
          break;
      }
  
      return prec;
    }
  
    // 11.5 Multiplicative Operators
    // 11.6 Additive Operators
    // 11.7 Bitwise Shift Operators
    // 11.8 Relational Operators
    // 11.9 Equality Operators
    // 11.10 Binary Bitwise Operators
    // 11.11 Binary Logical Operators
  
    function parseBinaryExpression() {
      var marker, markers, expr, token, prec, stack, right, operator, left, i;
  
      marker = lookahead;
      left = parseUnaryExpression();
  
      token = lookahead;
      prec = binaryPrecedence(token);
      if (prec === 0) {
        return left;
      }
      token.prec = prec;
      lex();
  
      markers = [marker, lookahead];
      right = parseUnaryExpression();
  
      stack = [left, token, right];
  
      while ((prec = binaryPrecedence(lookahead)) > 0) {
  
        // Reduce: make a binary expression from the three topmost entries.
        while ((stack.length > 2) && (prec <= stack[stack.length - 2].prec)) {
          right = stack.pop();
          operator = stack.pop().value;
          left = stack.pop();
          markers.pop();
          expr = finishBinaryExpression(operator, left, right);
          stack.push(expr);
        }
  
        // Shift.
        token = lex();
        token.prec = prec;
        stack.push(token);
        markers.push(lookahead);
        expr = parseUnaryExpression();
        stack.push(expr);
      }
  
      // Final reduce to clean-up the stack.
      i = stack.length - 1;
      expr = stack[i];
      markers.pop();
      while (i > 1) {
        markers.pop();
        expr = finishBinaryExpression(stack[i - 1].value, stack[i - 2], expr);
        i -= 2;
      }
  
      return expr;
    }
  
    // 11.12 Conditional Operator
  
    function parseConditionalExpression() {
      var expr, consequent, alternate;
  
      expr = parseBinaryExpression();
  
      if (match('?')) {
        lex();
        consequent = parseConditionalExpression();
        expect(':');
        alternate = parseConditionalExpression();
  
        expr = finishConditionalExpression(expr, consequent, alternate);
      }
  
      return expr;
    }
  
    // 11.14 Comma Operator
  
    function parseExpression() {
      var expr = parseConditionalExpression();
  
      if (match(',')) {
        throw new Error(DISABLED); // no sequence expressions
      }
  
      return expr;
    }
  
    function parse$3(code) {
      source$1 = code;
      index = 0;
      length = source$1.length;
      lookahead = null;
  
      peek$1();
  
      var expr = parseExpression();
  
      if (lookahead.type !== TokenEOF) {
        throw new Error("Unexpect token after expression.");
      }
      return expr;
    }
  
    var constants = {
      NaN:       'NaN',
      E:         'Math.E',
      LN2:       'Math.LN2',
      LN10:      'Math.LN10',
      LOG2E:     'Math.LOG2E',
      LOG10E:    'Math.LOG10E',
      PI:        'Math.PI',
      SQRT1_2:   'Math.SQRT1_2',
      SQRT2:     'Math.SQRT2',
      MIN_VALUE: 'Number.MIN_VALUE',
      MAX_VALUE: 'Number.MAX_VALUE'
    };
  
    function functions(codegen) {
  
      function fncall(name, args, cast, type) {
        var obj = codegen(args[0]);
        if (cast) {
          obj = cast + '(' + obj + ')';
          if (cast.lastIndexOf('new ', 0) === 0) obj = '(' + obj + ')';
        }
        return obj + '.' + name + (type < 0 ? '' : type === 0 ?
          '()' :
          '(' + args.slice(1).map(codegen).join(',') + ')');
      }
  
      function fn(name, cast, type) {
        return function(args) {
          return fncall(name, args, cast, type);
        };
      }
  
      var DATE = 'new Date',
          STRING = 'String',
          REGEXP = 'RegExp';
  
      return {
        // MATH functions
        isNaN:    'isNaN',
        isFinite: 'isFinite',
        abs:      'Math.abs',
        acos:     'Math.acos',
        asin:     'Math.asin',
        atan:     'Math.atan',
        atan2:    'Math.atan2',
        ceil:     'Math.ceil',
        cos:      'Math.cos',
        exp:      'Math.exp',
        floor:    'Math.floor',
        log:      'Math.log',
        max:      'Math.max',
        min:      'Math.min',
        pow:      'Math.pow',
        random:   'Math.random',
        round:    'Math.round',
        sin:      'Math.sin',
        sqrt:     'Math.sqrt',
        tan:      'Math.tan',
  
        clamp: function(args) {
          if (args.length < 3) error('Missing arguments to clamp function.');
          if (args.length > 3) error('Too many arguments to clamp function.');
          var a = args.map(codegen);
          return 'Math.max('+a[1]+', Math.min('+a[2]+','+a[0]+'))';
        },
  
        // DATE functions
        now:             'Date.now',
        utc:             'Date.UTC',
        datetime:        DATE,
        date:            fn('getDate', DATE, 0),
        day:             fn('getDay', DATE, 0),
        year:            fn('getFullYear', DATE, 0),
        month:           fn('getMonth', DATE, 0),
        hours:           fn('getHours', DATE, 0),
        minutes:         fn('getMinutes', DATE, 0),
        seconds:         fn('getSeconds', DATE, 0),
        milliseconds:    fn('getMilliseconds', DATE, 0),
        time:            fn('getTime', DATE, 0),
        timezoneoffset:  fn('getTimezoneOffset', DATE, 0),
        utcdate:         fn('getUTCDate', DATE, 0),
        utcday:          fn('getUTCDay', DATE, 0),
        utcyear:         fn('getUTCFullYear', DATE, 0),
        utcmonth:        fn('getUTCMonth', DATE, 0),
        utchours:        fn('getUTCHours', DATE, 0),
        utcminutes:      fn('getUTCMinutes', DATE, 0),
        utcseconds:      fn('getUTCSeconds', DATE, 0),
        utcmilliseconds: fn('getUTCMilliseconds', DATE, 0),
  
        // sequence functions
        length:      fn('length', null, -1),
        join:        fn('join', null),
        indexof:     fn('indexOf', null),
        lastindexof: fn('lastIndexOf', null),
        slice:       fn('slice', null),
  
        reverse: function(args) {
          return '('+codegen(args[0])+').slice().reverse()';
        },
  
        // STRING functions
        parseFloat:  'parseFloat',
        parseInt:    'parseInt',
        upper:       fn('toUpperCase', STRING, 0),
        lower:       fn('toLowerCase', STRING, 0),
        substring:   fn('substring', STRING),
        split:       fn('split', STRING),
        replace:     fn('replace', STRING),
        trim:        fn('trim', STRING, 0),
  
        // REGEXP functions
        regexp:  REGEXP,
        test:    fn('test', REGEXP),
  
        // Control Flow functions
        if: function(args) {
            if (args.length < 3) error('Missing arguments to if function.');
            if (args.length > 3) error('Too many arguments to if function.');
            var a = args.map(codegen);
            return '('+a[0]+'?'+a[1]+':'+a[2]+')';
          }
      };
    }
  
    function stripQuotes(s) {
      var n = s && s.length - 1;
      return n && (
          (s[0]==='"' && s[n]==='"') ||
          (s[0]==='\'' && s[n]==='\'')
        ) ? s.slice(1, -1) : s;
    }
  
    function codegen(opt) {
      opt = opt || {};
  
      var whitelist = opt.whitelist ? toSet(opt.whitelist) : {},
          blacklist = opt.blacklist ? toSet(opt.blacklist) : {},
          constants$1 = opt.constants || constants,
          functions$1 = (opt.functions || functions)(visit),
          globalvar = opt.globalvar,
          fieldvar = opt.fieldvar,
          globals = {},
          fields = {},
          memberDepth = 0;
  
      var outputGlobal = isFunction(globalvar)
        ? globalvar
        : function (id) { return globalvar + '["' + id + '"]'; };
  
      function visit(ast) {
        if (isString(ast)) return ast;
        var generator = Generators[ast.type];
        if (generator == null) error('Unsupported type: ' + ast.type);
        return generator(ast);
      }
  
      var Generators = {
        Literal: function(n) {
            return n.raw;
          },
  
        Identifier: function(n) {
          var id = n.name;
          if (memberDepth > 0) {
            return id;
          } else if (blacklist.hasOwnProperty(id)) {
            return error('Illegal identifier: ' + id);
          } else if (constants$1.hasOwnProperty(id)) {
            return constants$1[id];
          } else if (whitelist.hasOwnProperty(id)) {
            return id;
          } else {
            globals[id] = 1;
            return outputGlobal(id);
          }
        },
  
        MemberExpression: function(n) {
            var d = !n.computed;
            var o = visit(n.object);
            if (d) memberDepth += 1;
            var p = visit(n.property);
            if (o === fieldvar) {
              // strip quotes to sanitize field name (#1653)
              fields[stripQuotes(p)] = 1;
            }
            if (d) memberDepth -= 1;
            return o + (d ? '.'+p : '['+p+']');
          },
  
        CallExpression: function(n) {
            if (n.callee.type !== 'Identifier') {
              error('Illegal callee type: ' + n.callee.type);
            }
            var callee = n.callee.name;
            var args = n.arguments;
            var fn = functions$1.hasOwnProperty(callee) && functions$1[callee];
            if (!fn) error('Unrecognized function: ' + callee);
            return isFunction(fn)
              ? fn(args)
              : fn + '(' + args.map(visit).join(',') + ')';
          },
  
        ArrayExpression: function(n) {
            return '[' + n.elements.map(visit).join(',') + ']';
          },
  
        BinaryExpression: function(n) {
            return '(' + visit(n.left) + n.operator + visit(n.right) + ')';
          },
  
        UnaryExpression: function(n) {
            return '(' + n.operator + visit(n.argument) + ')';
          },
  
        ConditionalExpression: function(n) {
            return '(' + visit(n.test) +
              '?' + visit(n.consequent) +
              ':' + visit(n.alternate) +
              ')';
          },
  
        LogicalExpression: function(n) {
            return '(' + visit(n.left) + n.operator + visit(n.right) + ')';
          },
  
        ObjectExpression: function(n) {
            return '{' + n.properties.map(visit).join(',') + '}';
          },
  
        Property: function(n) {
            memberDepth += 1;
            var k = visit(n.key);
            memberDepth -= 1;
            return k + ':' + visit(n.value);
          }
      };
  
      function codegen(ast) {
        var result = {
          code:    visit(ast),
          globals: Object.keys(globals),
          fields:  Object.keys(fields)
        };
        globals = {};
        fields = {};
        return result;
      }
  
      codegen.functions = functions$1;
      codegen.constants = constants$1;
  
      return codegen;
    }
  
    const Intersect = 'intersect';
    const Union = 'union';
  
    var TYPE_ENUM = 'E',
        TYPE_RANGE_INC = 'R',
        TYPE_RANGE_EXC = 'R-E',
        TYPE_RANGE_LE = 'R-LE',
        TYPE_RANGE_RE = 'R-RE',
        UNIT_INDEX = 'index:unit';
  
    // TODO: revisit date coercion?
    function testPoint(datum, entry) {
      var fields = entry.fields,
          values = entry.values,
          n = fields.length,
          i = 0, dval, f;
  
      for (; i<n; ++i) {
        f = fields[i];
        f.getter = field.getter || field(f.field);
        dval = f.getter(datum);
  
        if (isDate(dval)) dval = toNumber(dval);
        if (isDate(values[i])) values[i] = toNumber(values[i]);
        if (isDate(values[i][0])) values[i] = values[i].map(toNumber);
  
        if (f.type === TYPE_ENUM) {
          // Enumerated fields can either specify individual values (single/multi selections)
          // or an array of values (interval selections).
          if(isArray(values[i]) ? values[i].indexOf(dval) < 0 : dval !== values[i]) {
            return false;
          }
        } else {
          if (f.type === TYPE_RANGE_INC) {
            if (!inrange(dval, values[i])) return false;
          } else if (f.type === TYPE_RANGE_RE) {
            // Discrete selection of bins test within the range [bin_start, bin_end).
            if (!inrange(dval, values[i], true, false)) return false;
          } else if (f.type === TYPE_RANGE_EXC) { // 'R-E'/'R-LE' included for completeness.
            if (!inrange(dval, values[i], false, false)) return false;
          } else if (f.type === TYPE_RANGE_LE) {
            if (!inrange(dval, values[i], false, true)) return false;
          }
        }
      }
  
      return true;
    }
  
    /**
     * Tests if a tuple is contained within an interactive selection.
     * @param {string} name - The name of the data set representing the selection.
     *  Tuples in the dataset are of the form
     *  {unit: string, fields: array<fielddef>, values: array<*>}.
     *  Fielddef is of the form
     *  {field: string, channel: string, type: 'E' | 'R'} where
     *  'type' identifies whether tuples in the dataset enumerate
     *  values for the field, or specify a continuous range.
     * @param {object} datum - The tuple to test for inclusion.
     * @param {string} op - The set operation for combining selections.
     *   One of 'intersect' or 'union' (default).
     * @return {boolean} - True if the datum is in the selection, false otherwise.
     */
    function selectionTest(name, datum, op) {
      var data = this.context.data[name],
          entries = data ? data.values.value : [],
          unitIdx = data ? data[UNIT_INDEX] && data[UNIT_INDEX].value : undefined,
          intersect = op === Intersect,
          n = entries.length,
          i = 0,
          entry, miss, count, unit, b;
  
      for (; i<n; ++i) {
        entry = entries[i];
  
        if (unitIdx && intersect) {
          // multi selections union within the same unit and intersect across units.
          miss = miss || {};
          count = miss[unit=entry.unit] || 0;
  
          // if we've already matched this unit, skip.
          if (count === -1) continue;
  
          b = testPoint(datum, entry);
          miss[unit] = b ? -1 : ++count;
  
          // if we match and there are no other units return true
          // if we've missed against all tuples in this unit return false
          if (b && unitIdx.size === 1) return true;
          if (!b && count === unitIdx.get(unit).count) return false;
        } else {
          b = testPoint(datum, entry);
  
          // if we find a miss and we do require intersection return false
          // if we find a match and we don't require intersection return true
          if (intersect ^ b) return b;
        }
      }
  
      // if intersecting and we made it here, then we saw no misses
      // if not intersecting, then we saw no matches
      // if no active selections, return false
      return n && intersect;
    }
  
    /**
     * Resolves selection for use as a scale domain or reads via the API.
     * @param {string} name - The name of the dataset representing the selection
     * @param {string} [op='union'] - The set operation for combining selections.
     *                 One of 'intersect' or 'union' (default).
     * @returns {object} An object of selected fields and values.
     */
    function selectionResolve(name, op) {
      var data = this.context.data[name],
        entries = data ? data.values.value : [],
        resolved = {}, types = {},
        entry, fields, values, unit, field, res, resUnit, type, union,
        n = entries.length, i = 0, j, m;
  
      // First union all entries within the same unit.
      for (; i < n; ++i) {
        entry = entries[i];
        unit = entry.unit;
        fields = entry.fields;
        values = entry.values;
  
        for (j = 0, m = fields.length; j < m; ++j) {
          field = fields[j];
          res = resolved[field.field] || (resolved[field.field] = {});
          resUnit = res[unit] || (res[unit] = []);
          types[field.field] = type = field.type.charAt(0);
          union = ops[type + '_union'];
          res[unit] = union(resUnit, array(values[j]));
        }
      }
  
      // Then resolve fields across units as per the op.
      op = op || Union;
      Object.keys(resolved).forEach(function (field) {
        resolved[field] = Object.keys(resolved[field])
          .map(function (unit) { return resolved[field][unit]; })
          .reduce(function (acc, curr) {
            return acc === undefined ? curr :
              ops[types[field] + '_' + op](acc, curr);
          });
      });
  
      return resolved;
    }
  
    var ops = {
      E_union: function(base, value) {
        if (!base.length) return value;
  
        var i = 0, n = value.length;
        for (; i<n; ++i) if (base.indexOf(value[i]) < 0) base.push(value[i]);
        return base;
      },
  
      E_intersect: function(base, value) {
        return !base.length ? value :
          base.filter(function (v) { return value.indexOf(v) >= 0; });
      },
  
      R_union: function(base, value) {
        var lo = toNumber(value[0]), hi = toNumber(value[1]);
        if (lo > hi) {
          lo = value[1];
          hi = value[0];
        }
  
        if (!base.length) return [lo, hi];
        if (base[0] > lo) base[0] = lo;
        if (base[1] < hi) base[1] = hi;
        return base;
      },
  
      R_intersect: function(base, value) {
        var lo = toNumber(value[0]), hi = toNumber(value[1]);
        if (lo > hi) {
          lo = value[1];
          hi = value[0];
        }
  
        if (!base.length) return [lo, hi];
        if (hi < base[0] || base[1] < lo) {
          return [];
        } else {
          if (base[0] < lo) base[0] = lo;
          if (base[1] > hi) base[1] = hi;
        }
        return base;
      }
    };
  
    const DataPrefix = ':',
          IndexPrefix = '@';
  
    function selectionVisitor(name, args, scope, params) {
      if (args[0].type !== Literal) error('First argument to selection functions must be a string literal.');
  
      const data = args[0].value,
            op = args.length >= 2 && peek(args).value,
            field = 'unit',
            indexName = IndexPrefix + field,
            dataName = DataPrefix + data;
  
      if (op === Intersect && !params.hasOwnProperty(indexName)) {
        params[indexName] = scope.getData(data).indataRef(scope, field);
      }
  
      if (!params.hasOwnProperty(dataName)) {
        params[dataName] = scope.getData(data).tuplesRef();
      }
    }
  
    function data$1(name) {
      const data = this.context.data[name];
      return data ? data.values.value : [];
    }
  
    function indata(name, field, value) {
      const index = this.context.data[name]['index:' + field],
            entry = index ? index.value.get(value) : undefined;
      return entry ? entry.count : entry;
    }
  
    function setdata(name, tuples) {
      const df = this.context.dataflow,
            data = this.context.data[name],
            input = data.input;
  
      df.pulse(input, df.changeset().remove(truthy).insert(tuples));
      return 1;
    }
  
    function encode$1(item, name, retval) {
      if (item) {
        const df = this.context.dataflow,
              target = item.mark.source;
        df.pulse(target, df.changeset().encode(item, name));
      }
      return retval !== undefined ? retval : item;
    }
  
    const formatCache = {};
  
    function formatter(type, method, specifier) {
      let k = type + ':' + specifier,
          e = formatCache[k];
      if (!e || e[0] !== method) {
        formatCache[k] = (e = [method, method(specifier)]);
      }
      return e[1];
    }
  
    function format$1(_, specifier) {
      return formatter('format', d3Format.format, specifier)(_);
    }
  
    function timeFormat(_, specifier) {
      return formatter('timeFormat', d3TimeFormat.timeFormat, specifier)(_);
    }
  
    function utcFormat(_, specifier) {
      return formatter('utcFormat', d3TimeFormat.utcFormat, specifier)(_);
    }
  
    function timeParse(_, specifier) {
      return formatter('timeParse', d3TimeFormat.timeParse, specifier)(_);
    }
  
    function utcParse(_, specifier) {
      return formatter('utcParse', d3TimeFormat.utcParse, specifier)(_);
    }
  
    var dateObj = new Date(2000, 0, 1);
  
    function time$1(month, day, specifier) {
      dateObj.setMonth(month);
      dateObj.setDate(day);
      return timeFormat(dateObj, specifier);
    }
  
    function monthFormat(month) {
      return time$1(month, 1, '%B');
    }
  
    function monthAbbrevFormat(month) {
      return time$1(month, 1, '%b');
    }
  
    function dayFormat(day) {
      return time$1(0, 2 + day, '%A');
    }
  
    function dayAbbrevFormat(day) {
      return time$1(0, 2 + day, '%a');
    }
  
    function getScale(name, ctx) {
      let s;
      return isFunction(name) ? name
        : isString(name) ? (s = ctx.scales[name]) && s.value
        : undefined;
    }
  
    function range$1(name, group) {
      const s = getScale(name, (group || this).context);
      return s && s.range ? s.range() : [];
    }
  
    function domain(name, group) {
      const s = getScale(name, (group || this).context);
      return s ? s.domain() : [];
    }
  
    function bandwidth(name, group) {
      const s = getScale(name, (group || this).context);
      return s && s.bandwidth ? s.bandwidth() : 0;
    }
  
    function bandspace(count, paddingInner, paddingOuter) {
      return bandSpace(count || 0, paddingInner || 0, paddingOuter || 0);
    }
  
    function copy(name, group) {
      const s = getScale(name, (group || this).context);
      return s ? s.copy() : undefined;
    }
  
    function scale$2(name, value, group) {
      const s = getScale(name, (group || this).context);
      return s && value !== undefined ? s(value) : undefined;
    }
  
    function invert(name, range, group) {
      const s = getScale(name, (group || this).context);
      return !s ? undefined
        : isArray(range) ? (s.invertRange || s.invert)(range)
        : (s.invert || s.invertExtent)(range);
    }
  
    function geoMethod(methodName, globalMethod) {
      return function(projection, geojson, group) {
        if (projection) {
          // projection defined, use it
          const p = getScale(projection, (group || this).context);
          return p && p.path[methodName](geojson);
        } else {
          // projection undefined, use global method
          return globalMethod(geojson);
        }
      };
    }
  
    const geoArea = geoMethod('area', d3Geo.geoArea);
    const geoBounds = geoMethod('bounds', d3Geo.geoBounds);
    const geoCentroid = geoMethod('centroid', d3Geo.geoCentroid);
  
    function inScope(item) {
      let group = this.context.group,
          value = false;
  
      if (group) while (item) {
        if (item === group) { value = true; break; }
        item = item.mark.group;
      }
      return value;
    }
  
    function intersect$2(b, opt, group) {
      if (!b) return [];
  
      const [u, v] = b,
            box = new Bounds().set(u[0], u[1], v[0], v[1]),
            scene = group || this.context.dataflow.scenegraph().root;
  
      return intersect(scene, box, filter$2(opt));
    }
  
    function filter$2(opt) {
      let p = null;
  
      if (opt) {
        const types = array(opt.marktype),
              names = array(opt.markname);
        p = _ => (!types.length || types.some(t => _.marktype === t))
              && (!names.length || names.some(s => _.name === s));
      }
  
      return p;
    }
  
    function log$2(df, method, args) {
      try {
        df[method].apply(df, ['EXPRESSION'].concat([].slice.call(args)));
      } catch (err) {
        df.warn(err);
      }
      return args[args.length-1];
    }
  
    function warn() {
      return log$2(this.context.dataflow, 'warn', arguments);
    }
  
    function info() {
      return log$2(this.context.dataflow, 'info', arguments);
    }
  
    function debug() {
      return log$2(this.context.dataflow, 'debug', arguments);
    }
  
    function merge$2() {
      var args = [].slice.call(arguments);
      args.unshift({});
      return extend.apply(null, args);
    }
  
    function equal(a, b) {
      return a === b || a !== a && b !== b ? true
        : isArray(a) && isArray(b) && a.length === b.length ? equalArray(a, b)
        : false;
    }
  
    function equalArray(a, b) {
      for (let i=0, n=a.length; i<n; ++i) {
        if (!equal(a[i], b[i])) return false;
      }
      return true;
    }
  
    function removePredicate(props) {
      return function(_) {
        for (let key in props) {
          if (!equal(_[key], props[key])) return false;
        }
        return true;
      };
    }
  
    function modify(name, insert, remove, toggle, modify, values) {
      let df = this.context.dataflow,
          data = this.context.data[name],
          input = data.input,
          changes = data.changes,
          stamp = df.stamp(),
          predicate, key;
  
      if (df._trigger === false || !(input.value.length || insert || toggle)) {
        // nothing to do!
        return 0;
      }
  
      if (!changes || changes.stamp < stamp) {
        data.changes = (changes = df.changeset());
        changes.stamp = stamp;
        df.runAfter(function() {
          data.modified = true;
          df.pulse(input, changes).run();
        }, true, 1);
      }
  
      if (remove) {
        predicate = remove === true ? truthy
          : (isArray(remove) || isTuple(remove)) ? remove
          : removePredicate(remove);
        changes.remove(predicate);
      }
  
      if (insert) {
        changes.insert(insert);
      }
  
      if (toggle) {
        predicate = removePredicate(toggle);
        if (input.value.some(predicate)) {
          changes.remove(predicate);
        } else {
          changes.insert(toggle);
        }
      }
  
      if (modify) {
        for (key in values) {
          changes.modify(modify, key, values[key]);
        }
      }
  
      return 1;
    }
  
    function pinchDistance(event) {
      const t = event.touches,
            dx = t[0].clientX - t[1].clientX,
            dy = t[0].clientY - t[1].clientY;
      return Math.sqrt(dx * dx + dy * dy);
    }
  
    function pinchAngle(event) {
      const t = event.touches;
      return Math.atan2(
        t[0].clientY - t[1].clientY,
        t[0].clientX - t[1].clientX
      );
    }
  
    function scaleGradient(scale, p0, p1, count, group) {
      scale = getScale(scale, (group || this).context);
  
      const gradient = Gradient(p0, p1);
  
      let stops = scale.domain(),
          min = stops[0],
          max = peek(stops),
          fraction = identity;
  
      if (!(max - min)) {
        // expand scale if domain has zero span, fix #1479
        scale = (scale.interpolator
          ? scale$1('sequential')().interpolator(scale.interpolator())
          : scale$1('linear')().interpolate(scale.interpolate()).range(scale.range())
        ).domain([min=0, max=1]);
      } else {
        fraction = scaleFraction(scale, min, max);
      }
  
      if (scale.ticks) {
        stops = scale.ticks(+count || 15);
        if (min !== stops[0]) stops.unshift(min);
        if (max !== peek(stops)) stops.push(max);
      }
  
      stops.forEach(_ => gradient.stop(fraction(_), scale(_)));
  
      return gradient;
    }
  
    function geoShape(projection, geojson, group) {
      const p = getScale(projection, (group || this).context);
      return function(context) {
        return p ? p.path.context(context)(geojson) : '';
      }
    }
  
    function pathShape(path) {
      let p = null;
      return function(context) {
        return context
          ? pathRender(context, (p = p || pathParse(path)))
          : path;
      };
    }
  
    const EMPTY = {};
  
    function datum(d) { return d.data; }
  
    function treeNodes(name, context) {
      const tree = data$1.call(context, name);
      return tree.root && tree.root.lookup || EMPTY;
    }
  
    function treePath(name, source, target) {
      const nodes = treeNodes(name, this),
            s = nodes[source],
            t = nodes[target];
      return s && t ? s.path(t).map(datum) : undefined;
    }
  
    function treeAncestors(name, node) {
      const n = treeNodes(name, this)[node];
      return n ? n.ancestors().map(datum) : undefined;
    }
  
    const _window = (typeof window !== 'undefined' && window) || null;
  
    function screen() {
      return _window ? _window.screen : {};
    }
  
    function windowSize() {
      return _window
        ? [_window.innerWidth, _window.innerHeight]
        : [undefined, undefined];
    }
  
    function containerSize() {
      const view = this.context.dataflow,
            el = view.container && view.container();
      return el
        ? [el.clientWidth, el.clientHeight]
        : [undefined, undefined];
    }
  
    const DataPrefix$1   = ':';
    const IndexPrefix$1  = '@';
    const ScalePrefix  = '%';
    const SignalPrefix = '$';
  
    function dataVisitor(name, args, scope, params) {
      if (args[0].type !== Literal) {
        error('First argument to data functions must be a string literal.');
      }
  
      const data = args[0].value,
            dataName = DataPrefix$1 + data;
  
      if (!params.hasOwnProperty(dataName)) {
        params[dataName] = scope.getData(data).tuplesRef();
      }
    }
  
    function indataVisitor(name, args, scope, params) {
      if (args[0].type !== Literal) error('First argument to indata must be a string literal.');
      if (args[1].type !== Literal) error('Second argument to indata must be a string literal.');
  
      const data = args[0].value,
            field = args[1].value,
            indexName = IndexPrefix$1 + field;
  
      if (!params.hasOwnProperty(indexName)) {
        params[indexName] = scope.getData(data).indataRef(scope, field);
      }
    }
  
    function scaleVisitor(name, args, scope, params) {
      if (args[0].type === Literal) {
        // add scale dependency
        addScaleDependency(scope, params, args[0].value);
      }
      else if (args[0].type === Identifier$1) {
        // indirect scale lookup; add all scales as parameters
        for (name in scope.scales) {
          addScaleDependency(scope, params, name);
        }
      }
    }
  
    function addScaleDependency(scope, params, name) {
      const scaleName = ScalePrefix + name;
      if (!params.hasOwnProperty(scaleName)) {
        try {
          params[scaleName] = scope.scaleRef(name);
        } catch (err) {
          // TODO: error handling? warning?
        }
      }
    }
  
    // Expression function context object
    const functionContext = {
      random: function() { return exports.random(); }, // override default
      isArray,
      isBoolean,
      isDate,
      isDefined: function(_) { return _ !== undefined; },
      isNumber,
      isObject,
      isRegExp,
      isString,
      isTuple,
      isValid: function(_) { return _ != null && _ === _; },
      toBoolean,
      toDate,
      toNumber,
      toString,
      flush,
      lerp,
      merge: merge$2,
      pad,
      peek,
      span,
      inrange,
      truncate,
      rgb: d3Color.rgb,
      lab: d3Color.lab,
      hcl: d3Color.hcl,
      hsl: d3Color.hsl,
      sequence: d3Array.range,
      format: format$1,
      utcFormat,
      utcParse,
      timeFormat,
      timeParse,
      monthFormat,
      monthAbbrevFormat,
      dayFormat,
      dayAbbrevFormat,
      quarter,
      utcquarter,
      warn,
      info,
      debug,
      extent,
      inScope,
      intersect: intersect$2,
      clampRange,
      pinchDistance,
      pinchAngle,
      screen,
      containerSize,
      windowSize,
      bandspace,
      setdata,
      pathShape,
      panLinear,
      panLog,
      panPow,
      panSymlog,
      zoomLinear,
      zoomLog,
      zoomPow,
      zoomSymlog,
      encode: encode$1,
      modify
    };
  
    const eventFunctions = ['view', 'item', 'group', 'xy', 'x', 'y'], // event functions
          eventPrefix = 'event.vega.', // event function prefix
          thisPrefix = 'this.', // function context prefix
          astVisitors = {}; // AST visitors for dependency analysis
  
    // Build expression function registry
    function buildFunctions(codegen) {
      const fn = functions(codegen);
      eventFunctions.forEach(name => fn[name] = eventPrefix + name);
      for (let name in functionContext) { fn[name] = thisPrefix + name; }
      return fn;
    }
  
    // Register an expression function
    function expressionFunction(name, fn, visitor) {
      if (arguments.length === 1) {
        return functionContext[name];
      }
  
      // register with the functionContext
      functionContext[name] = fn;
  
      // if there is an astVisitor register that, too
      if (visitor) astVisitors[name] = visitor;
  
      // if the code generator has already been initialized,
      // we need to also register the function with it
      if (codeGenerator) codeGenerator.functions[name] = thisPrefix + name;
      return this;
    }
  
    // register expression functions with ast visitors
    expressionFunction('bandwidth', bandwidth, scaleVisitor);
    expressionFunction('copy', copy, scaleVisitor);
    expressionFunction('domain', domain, scaleVisitor);
    expressionFunction('range', range$1, scaleVisitor);
    expressionFunction('invert', invert, scaleVisitor);
    expressionFunction('scale', scale$2, scaleVisitor);
    expressionFunction('gradient', scaleGradient, scaleVisitor);
    expressionFunction('geoArea', geoArea, scaleVisitor);
    expressionFunction('geoBounds', geoBounds, scaleVisitor);
    expressionFunction('geoCentroid', geoCentroid, scaleVisitor);
    expressionFunction('geoShape', geoShape, scaleVisitor);
    expressionFunction('indata', indata, indataVisitor);
    expressionFunction('data', data$1, dataVisitor);
    expressionFunction('treePath', treePath, dataVisitor);
    expressionFunction('treeAncestors', treeAncestors, dataVisitor);
  
    // register Vega-Lite selection functions
    expressionFunction('vlSelectionTest', selectionTest, selectionVisitor);
    expressionFunction('vlSelectionResolve', selectionResolve, selectionVisitor);
  
    // Export code generator and parameters
    const codegenParams = {
      blacklist:  ['_'],
      whitelist:  ['datum', 'event', 'item'],
      fieldvar:   'datum',
      globalvar:  function(id) { return '_[' + $(SignalPrefix + id) + ']'; },
      functions:  buildFunctions,
      constants:  constants,
      visitors:   astVisitors
    };
  
    var codeGenerator = codegen(codegenParams);
  
    /**
     * Parse an expression given the argument signature and body code.
     */
    function expression(args, code, ctx) {
      // wrap code in return statement if expression does not terminate
      if (code[code.length-1] !== ';') {
        code = 'return(' + code + ');';
      }
      var fn = Function.apply(null, args.concat(code));
      return ctx && ctx.functions ? fn.bind(ctx.functions) : fn;
    }
  
    /**
     * Parse an expression used to update an operator value.
     */
    function operatorExpression(code, ctx) {
      return expression(['_'], code, ctx);
    }
  
    /**
     * Parse an expression provided as an operator parameter value.
     */
    function parameterExpression(code, ctx) {
      return expression(['datum', '_'], code, ctx);
    }
  
    /**
     * Parse an expression applied to an event stream.
     */
    function eventExpression(code, ctx) {
      return expression(['event'], code, ctx);
    }
  
    /**
     * Parse an expression used to handle an event-driven operator update.
     */
    function handlerExpression(code, ctx) {
      return expression(['_', 'event'], code, ctx);
    }
  
    /**
     * Parse an expression that performs visual encoding.
     */
    function encodeExpression(code, ctx) {
      return expression(['item', '_'], code, ctx);
    }
  
    /**
     * Parse a set of operator parameters.
     */
    function parseParameters(spec, ctx, params) {
      params = params || {};
      var key, value;
  
      for (key in spec) {
        value = spec[key];
  
        params[key] = isArray(value)
          ? value.map(function(v) { return parseParameter(v, ctx, params); })
          : parseParameter(value, ctx, params);
      }
      return params;
    }
  
    /**
     * Parse a single parameter.
     */
    function parseParameter(spec, ctx, params) {
      if (!spec || !isObject(spec)) return spec;
  
      for (var i=0, n=PARSERS.length, p; i<n; ++i) {
        p = PARSERS[i];
        if (spec.hasOwnProperty(p.key)) {
          return p.parse(spec, ctx, params);
        }
      }
      return spec;
    }
  
    /** Reference parsers. */
    var PARSERS = [
      {key: '$ref',      parse: getOperator},
      {key: '$key',      parse: getKey},
      {key: '$expr',     parse: getExpression},
      {key: '$field',    parse: getField$1},
      {key: '$encode',   parse: getEncode},
      {key: '$compare',  parse: getCompare},
      {key: '$context',  parse: getContext},
      {key: '$subflow',  parse: getSubflow},
      {key: '$tupleid',  parse: getTupleId}
    ];
  
    /**
     * Resolve an operator reference.
     */
    function getOperator(_, ctx) {
      return ctx.get(_.$ref) || error('Operator not defined: ' + _.$ref);
    }
  
    /**
     * Resolve an expression reference.
     */
    function getExpression(_, ctx, params) {
      if (_.$params) { // parse expression parameters
        parseParameters(_.$params, ctx, params);
      }
      var k = 'e:' + _.$expr + '_' + _.$name;
      return ctx.fn[k]
        || (ctx.fn[k] = accessor(parameterExpression(_.$expr, ctx), _.$fields, _.$name));
    }
  
    /**
     * Resolve a key accessor reference.
     */
    function getKey(_, ctx) {
      var k = 'k:' + _.$key + '_' + (!!_.$flat);
      return ctx.fn[k] || (ctx.fn[k] = key(_.$key, _.$flat));
    }
  
    /**
     * Resolve a field accessor reference.
     */
    function getField$1(_, ctx) {
      if (!_.$field) return null;
      var k = 'f:' + _.$field + '_' + _.$name;
      return ctx.fn[k] || (ctx.fn[k] = field(_.$field, _.$name));
    }
  
    /**
     * Resolve a comparator function reference.
     */
    function getCompare(_, ctx) {
      var k = 'c:' + _.$compare + '_' + _.$order,
          c = array(_.$compare).map(function(_) {
            return (_ && _.$tupleid) ? tupleid : _;
          });
      return ctx.fn[k] || (ctx.fn[k] = compare(c, _.$order));
    }
  
    /**
     * Resolve an encode operator reference.
     */
    function getEncode(_, ctx) {
      var spec = _.$encode,
          encode = {}, name, enc;
  
      for (name in spec) {
        enc = spec[name];
        encode[name] = accessor(encodeExpression(enc.$expr, ctx), enc.$fields);
        encode[name].output = enc.$output;
      }
      return encode;
    }
  
    /**
     * Resolve a context reference.
     */
    function getContext(_, ctx) {
      return ctx;
    }
  
    /**
     * Resolve a recursive subflow specification.
     */
    function getSubflow(_, ctx) {
      var spec = _.$subflow;
      return function(dataflow, key, parent) {
        var subctx = parse$4(spec, ctx.fork()),
            op = subctx.get(spec.operators[0].id),
            p = subctx.signals.parent;
        if (p) p.set(parent);
        return op;
      };
    }
  
    /**
     * Resolve a tuple id reference.
     */
    function getTupleId() {
      return tupleid;
    }
  
    function canonicalType(type) {
      return (type + '').toLowerCase();
    }
    function isOperator(type) {
       return canonicalType(type) === 'operator';
    }
  
    function isCollect(type) {
      return canonicalType(type) === 'collect';
    }
  
    /**
     * Parse a dataflow operator.
     */
    function parseOperator(spec, ctx) {
      if (isOperator(spec.type) || !spec.type) {
        ctx.operator(spec,
          spec.update ? operatorExpression(spec.update, ctx) : null);
      } else {
        ctx.transform(spec, spec.type);
      }
    }
  
    /**
     * Parse and assign operator parameters.
     */
    function parseOperatorParameters(spec, ctx) {
      if (spec.params) {
        var op = ctx.get(spec.id);
        if (!op) error('Invalid operator id: ' + spec.id);
        ctx.dataflow.connect(op, op.parameters(
          parseParameters(spec.params, ctx),
          spec.react,
          spec.initonly
        ));
      }
    }
  
    /**
     * Parse an event stream specification.
     */
    function parseStream(spec, ctx) {
      var filter = spec.filter != null ? eventExpression(spec.filter, ctx) : undefined,
          stream = spec.stream != null ? ctx.get(spec.stream) : undefined,
          args;
  
      if (spec.source) {
        stream = ctx.events(spec.source, spec.type, filter);
      }
      else if (spec.merge) {
        args = spec.merge.map(ctx.get.bind(ctx));
        stream = args[0].merge.apply(args[0], args.slice(1));
      }
  
      if (spec.between) {
        args = spec.between.map(ctx.get.bind(ctx));
        stream = stream.between(args[0], args[1]);
      }
  
      if (spec.filter) {
        stream = stream.filter(filter);
      }
  
      if (spec.throttle != null) {
        stream = stream.throttle(+spec.throttle);
      }
  
      if (spec.debounce != null) {
        stream = stream.debounce(+spec.debounce);
      }
  
      if (stream == null) {
        error('Invalid stream definition: ' + JSON.stringify(spec));
      }
  
      if (spec.consume) stream.consume(true);
  
      ctx.stream(spec, stream);
    }
  
    /**
     * Parse an event-driven operator update.
     */
    function parseUpdate(spec, ctx) {
      var srcid = isObject(srcid = spec.source) ? srcid.$ref : srcid,
          source = ctx.get(srcid),
          target = null,
          update = spec.update,
          params = undefined;
  
      if (!source) error('Source not defined: ' + spec.source);
  
      if (spec.target && spec.target.$expr) {
        target = eventExpression(spec.target.$expr, ctx);
      } else {
        target = ctx.get(spec.target);
      }
  
      if (update && update.$expr) {
        if (update.$params) {
          params = parseParameters(update.$params, ctx);
        }
        update = handlerExpression(update.$expr, ctx);
      }
  
      ctx.update(spec, source, target, update, params);
    }
  
    /**
     * Parse a serialized dataflow specification.
     */
    function parse$4(spec, ctx) {
      var operators = spec.operators || [];
  
      // parse background
      if (spec.background) {
        ctx.background = spec.background;
      }
  
      // parse event configuration
      if (spec.eventConfig) {
        ctx.eventConfig = spec.eventConfig;
      }
  
      // parse operators
      operators.forEach(function(entry) {
        parseOperator(entry, ctx);
      });
  
      // parse operator parameters
      operators.forEach(function(entry) {
        parseOperatorParameters(entry, ctx);
      });
  
      // parse streams
      (spec.streams || []).forEach(function(entry) {
        parseStream(entry, ctx);
      });
  
      // parse updates
      (spec.updates || []).forEach(function(entry) {
        parseUpdate(entry, ctx);
      });
  
      return ctx.resolve();
    }
  
    var SKIP$3 = {skip: true};
  
    function getState(options) {
      var ctx = this,
          state = {};
  
      if (options.signals) {
        var signals = (state.signals = {});
        Object.keys(ctx.signals).forEach(function(key) {
          var op = ctx.signals[key];
          if (options.signals(key, op)) {
            signals[key] = op.value;
          }
        });
      }
  
      if (options.data) {
        var data = (state.data = {});
        Object.keys(ctx.data).forEach(function(key) {
          var dataset = ctx.data[key];
          if (options.data(key, dataset)) {
            data[key] = dataset.input.value;
          }
        });
      }
  
      if (ctx.subcontext && options.recurse !== false) {
        state.subcontext = ctx.subcontext.map(function(ctx) {
          return ctx.getState(options);
        });
      }
  
      return state;
    }
  
    function setState(state) {
      var ctx = this,
          df = ctx.dataflow,
          data = state.data,
          signals = state.signals;
  
      Object.keys(signals || {}).forEach(function(key) {
        df.update(ctx.signals[key], signals[key], SKIP$3);
      });
  
      Object.keys(data || {}).forEach(function(key) {
        df.pulse(
          ctx.data[key].input,
          df.changeset().remove(truthy).insert(data[key])
        );
      });
  
      (state.subcontext  || []).forEach(function(substate, i) {
        var subctx = ctx.subcontext[i];
        if (subctx) subctx.setState(substate);
      });
    }
  
    /**
     * Context objects store the current parse state.
     * Enables lookup of parsed operators, event streams, accessors, etc.
     * Provides a 'fork' method for creating child contexts for subflows.
     */
    function context$2(df, transforms, functions) {
      return new Context(df, transforms, functions);
    }
  
    function Context(df, transforms, functions) {
      this.dataflow = df;
      this.transforms = transforms;
      this.events = df.events.bind(df);
      this.signals = {};
      this.scales = {};
      this.nodes = {};
      this.data = {};
      this.fn = {};
      if (functions) {
        this.functions = Object.create(functions);
        this.functions.context = this;
      }
    }
  
    function ContextFork(ctx) {
      this.dataflow = ctx.dataflow;
      this.transforms = ctx.transforms;
      this.functions = ctx.functions;
      this.events = ctx.events;
      this.signals = Object.create(ctx.signals);
      this.scales = Object.create(ctx.scales);
      this.nodes = Object.create(ctx.nodes);
      this.data = Object.create(ctx.data);
      this.fn = Object.create(ctx.fn);
      if (ctx.functions) {
        this.functions = Object.create(ctx.functions);
        this.functions.context = this;
      }
    }
  
    Context.prototype = ContextFork.prototype = {
      fork: function() {
        var ctx = new ContextFork(this);
        (this.subcontext || (this.subcontext = [])).push(ctx);
        return ctx;
      },
      get: function(id) {
        return this.nodes[id];
      },
      set: function(id, node) {
        return this.nodes[id] = node;
      },
      add: function(spec, op) {
        var ctx = this,
            df = ctx.dataflow,
            data;
  
        ctx.set(spec.id, op);
  
        if (isCollect(spec.type) && (data = spec.value)) {
          if (data.$ingest) {
            df.ingest(op, data.$ingest, data.$format);
          } else if (data.$request) {
            df.preload(op, data.$request, data.$format);
          } else {
            df.pulse(op, df.changeset().insert(data));
          }
        }
  
        if (spec.root) {
          ctx.root = op;
        }
  
        if (spec.parent) {
          var p = ctx.get(spec.parent.$ref);
          if (p) {
            df.connect(p, [op]);
            op.targets().add(p);
          } else {
            (ctx.unresolved = ctx.unresolved || []).push(function() {
              p = ctx.get(spec.parent.$ref);
              df.connect(p, [op]);
              op.targets().add(p);
            });
          }
        }
  
        if (spec.signal) {
          ctx.signals[spec.signal] = op;
        }
  
        if (spec.scale) {
          ctx.scales[spec.scale] = op;
        }
  
        if (spec.data) {
          for (var name in spec.data) {
            data = ctx.data[name] || (ctx.data[name] = {});
            spec.data[name].forEach(function(role) { data[role] = op; });
          }
        }
      },
      resolve: function() {
        (this.unresolved || []).forEach(function(fn) { fn(); });
        delete this.unresolved;
        return this;
      },
      operator: function(spec, update) {
        this.add(spec, this.dataflow.add(spec.value, update));
      },
      transform: function(spec, type) {
        this.add(spec, this.dataflow.add(this.transforms[canonicalType(type)]));
      },
      stream: function(spec, stream) {
        this.set(spec.id, stream);
      },
      update: function(spec, stream, target, update, params) {
        this.dataflow.on(stream, target, update, params, spec.options);
      },
      getState: getState,
      setState: setState
    };
  
    function runtime(view, spec, functions) {
      var fn = functions || functionContext;
      return parse$4(spec, context$2(view, transforms, fn));
    }
  
    function scale$3(name) {
      var scales = this._runtime.scales;
      if (!scales.hasOwnProperty(name)) {
        error('Unrecognized scale or projection: ' + name);
      }
      return scales[name].value;
    }
  
    var Width = 'width',
        Height = 'height',
        Padding$1 = 'padding',
        Skip = {skip: true};
  
    function viewWidth(view, width) {
      var a = view.autosize(),
          p = view.padding();
      return width - (a && a.contains === Padding$1 ? p.left + p.right : 0);
    }
  
    function viewHeight(view, height) {
      var a = view.autosize(),
          p = view.padding();
      return height - (a && a.contains === Padding$1 ? p.top + p.bottom : 0);
    }
  
    function initializeResize(view) {
      var s = view._signals,
          w = s[Width],
          h = s[Height],
          p = s[Padding$1];
  
      function resetSize() {
        view._autosize = view._resize = 1;
      }
  
      // respond to width signal
      view._resizeWidth = view.add(null,
        function(_) {
          view._width = _.size;
          view._viewWidth = viewWidth(view, _.size);
          resetSize();
        },
        {size: w}
      );
  
      // respond to height signal
      view._resizeHeight = view.add(null,
        function(_) {
          view._height = _.size;
          view._viewHeight = viewHeight(view, _.size);
          resetSize();
        },
        {size: h}
      );
  
      // respond to padding signal
      var resizePadding = view.add(null, resetSize, {pad: p});
  
      // set rank to run immediately after source signal
      view._resizeWidth.rank = w.rank + 1;
      view._resizeHeight.rank = h.rank + 1;
      resizePadding.rank = p.rank + 1;
    }
  
    function resizeView(viewWidth, viewHeight, width, height, origin, auto) {
      this.runAfter(function(view) {
        var rerun = 0;
  
        // reset autosize flag
        view._autosize = 0;
  
        // width value changed: update signal, skip resize op
        if (view.width() !== width) {
          rerun = 1;
          view.signal(Width, width, Skip); // set width, skip update calc
          view._resizeWidth.skip(true); // skip width resize handler
        }
  
        // height value changed: update signal, skip resize op
        if (view.height() !== height) {
          rerun = 1;
          view.signal(Height, height, Skip); // set height, skip update calc
          view._resizeHeight.skip(true); // skip height resize handler
        }
  
        // view width changed: update view property, set resize flag
        if (view._viewWidth !== viewWidth) {
          view._resize = 1;
          view._viewWidth = viewWidth;
        }
  
        // view height changed: update view property, set resize flag
        if (view._viewHeight !== viewHeight) {
          view._resize = 1;
          view._viewHeight = viewHeight;
        }
  
        // origin changed: update view property, set resize flag
        if (view._origin[0] !== origin[0] || view._origin[1] !== origin[1]) {
          view._resize = 1;
          view._origin = origin;
        }
  
        // run dataflow on width/height signal change
        if (rerun) view.run('enter');
        if (auto) view.runAfter(v => v.resize());
      }, false, 1);
    }
  
    /**
     * Get the current view state, consisting of signal values and/or data sets.
     * @param {object} [options] - Options flags indicating which state to export.
     *   If unspecified, all signals and data sets will be exported.
     * @param {function(string, Operator):boolean} [options.signals] - Optional
     *   predicate function for testing if a signal should be included in the
     *   exported state. If unspecified, all signals will be included, except for
     *   those named 'parent' or those which refer to a Transform value.
     * @param {function(string, object):boolean} [options.data] - Optional
     *   predicate function for testing if a data set's input should be included
     *   in the exported state. If unspecified, all data sets that have been
     *   explicitly modified will be included.
     * @param {boolean} [options.recurse=true] - Flag indicating if the exported
     *   state should recursively include state from group mark sub-contexts.
     * @return {object} - An object containing the exported state values.
     */
    function getState$1(options) {
      return this._runtime.getState(options || {
        data:    dataTest,
        signals: signalTest,
        recurse: true
      });
    }
  
    function dataTest(name, data) {
      return data.modified
          && isArray(data.input.value)
          && name.indexOf('_:vega:_');
    }
  
    function signalTest(name, op) {
      return !(name === 'parent' || op instanceof transforms.proxy);
    }
  
    /**
     * Sets the current view state and updates the view by invoking run.
     * @param {object} state - A state object containing signal and/or
     *   data set values, following the format used by the getState method.
     * @return {View} - This view instance.
     */
    function setState$1(state) {
      this.runAsync(null,
        v => { v._trigger = false; v._runtime.setState(state); },
        v => { v._trigger = true; }
      );
      return this;
    }
  
    function timer(callback, delay) {
      function tick(elapsed) {
        callback({timestamp: Date.now(), elapsed: elapsed});
      }
      this._timers.push(d3Timer.interval(tick, delay));
    }
  
    function defaultTooltip$1(handler, event, item, value) {
      var el = handler.element();
      if (el) el.setAttribute('title', formatTooltip(value));
    }
  
    function formatTooltip(value) {
      return value == null ? ''
        : isArray(value) ? formatArray(value)
        : isObject(value) && !isDate(value) ? formatObject(value)
        : value + '';
    }
  
    function formatObject(obj) {
      return Object.keys(obj).map(function(key) {
        var v = obj[key];
        return key + ': ' + (isArray(v) ? formatArray(v) : formatValue$1(v));
      }).join('\n');
    }
  
    function formatArray(value) {
      return '[' + value.map(formatValue$1).join(', ') + ']';
    }
  
    function formatValue$1(value) {
      return isArray(value) ? '[\u2026]'
        : isObject(value) && !isDate(value) ? '{\u2026}'
        : value;
    }
  
    /**
     * Create a new View instance from a Vega dataflow runtime specification.
     * The generated View will not immediately be ready for display. Callers
     * should also invoke the initialize method (e.g., to set the parent
     * DOM element in browser-based deployment) and then invoke the run
     * method to evaluate the dataflow graph. Rendering will automatically
     * be peformed upon dataflow runs.
     * @constructor
     * @param {object} spec - The Vega dataflow runtime specification.
     */
    function View(spec, options) {
      var view = this;
      options = options || {};
  
      Dataflow.call(view);
      if (options.loader) view.loader(options.loader);
      if (options.logger) view.logger(options.logger);
      if (options.logLevel != null) view.logLevel(options.logLevel);
  
      view._el = null;
      view._elBind = null;
      view._renderType = options.renderer || RenderType.Canvas;
      view._scenegraph = new Scenegraph();
      var root = view._scenegraph.root;
  
      // initialize renderer, handler and event management
      view._renderer = null;
      view._tooltip = options.tooltip || defaultTooltip$1,
      view._redraw = true;
      view._handler = new CanvasHandler().scene(root);
      view._preventDefault = false;
      view._timers = [];
      view._eventListeners = [];
      view._resizeListeners = [];
  
      // initialize dataflow graph
      var ctx = runtime(view, spec, options.functions);
      view._runtime = ctx;
      view._signals = ctx.signals;
      view._bind = (spec.bindings || []).map(function(_) {
        return {
          state: null,
          param: extend({}, _)
        };
      });
  
      // initialize scenegraph
      if (ctx.root) ctx.root.set(root);
      root.source = ctx.data.root.input;
      view.pulse(
        ctx.data.root.input,
        view.changeset().insert(root.items)
      );
  
      // initialize background color
      view._background = options.background || ctx.background || null;
  
      // initialize event configuration
      view._eventConfig = initializeEventConfig(ctx.eventConfig);
  
      // initialize view size
      view._width = view.width();
      view._height = view.height();
      view._viewWidth = viewWidth(view, view._width);
      view._viewHeight = viewHeight(view, view._height);
      view._origin = [0, 0];
      view._resize = 0;
      view._autosize = 1;
      initializeResize(view);
  
      // initialize cursor
      cursor(view);
  
      // initialize hover proessing, if requested
      if (options.hover) view.hover();
  
      // initialize DOM container(s) and renderer
      if (options.container) view.initialize(options.container, options.bind);
    }
  
    var prototype$1m = inherits(View, Dataflow);
  
    // -- DATAFLOW / RENDERING ----
  
    prototype$1m.evaluate = async function(encode, prerun, postrun) {
      // evaluate dataflow and prerun
      await Dataflow.prototype.evaluate.call(this, encode, prerun);
  
      // render as needed
      if (this._redraw || this._resize) {
        try {
          if (this._renderer) {
            if (this._resize) {
              this._resize = 0;
              resizeRenderer(this);
            }
            await this._renderer.renderAsync(this._scenegraph.root);
          }
          this._redraw = false;
        } catch (e) {
          this.error(e);
        }
      }
  
      // evaluate postrun
      if (postrun) asyncCallback(this, postrun);
  
      return this;
    };
  
    prototype$1m.dirty = function(item) {
      this._redraw = true;
      this._renderer && this._renderer.dirty(item);
    };
  
    // -- GET / SET ----
  
    prototype$1m.container = function() {
      return this._el;
    };
  
    prototype$1m.scenegraph = function() {
      return this._scenegraph;
    };
  
    prototype$1m.origin = function() {
      return this._origin.slice();
    };
  
    function lookupSignal(view, name) {
      return view._signals.hasOwnProperty(name)
        ? view._signals[name]
        : error('Unrecognized signal name: ' + $(name));
    }
  
    prototype$1m.signal = function(name, value, options) {
      var op = lookupSignal(this, name);
      return arguments.length === 1
        ? op.value
        : this.update(op, value, options);
    };
  
    prototype$1m.background = function(_) {
      if (arguments.length) {
        this._background = _;
        this._resize = 1;
        return this;
      } else {
        return this._background;
      }
    };
  
    prototype$1m.width = function(_) {
      return arguments.length ? this.signal('width', _) : this.signal('width');
    };
  
    prototype$1m.height = function(_) {
      return arguments.length ? this.signal('height', _) : this.signal('height');
    };
  
    prototype$1m.padding = function(_) {
      return arguments.length ? this.signal('padding', _) : this.signal('padding');
    };
  
    prototype$1m.autosize = function(_) {
      return arguments.length ? this.signal('autosize', _) : this.signal('autosize');
    };
  
    prototype$1m.renderer = function(type) {
      if (!arguments.length) return this._renderType;
      if (!renderModule(type)) error('Unrecognized renderer type: ' + type);
      if (type !== this._renderType) {
        this._renderType = type;
        this._resetRenderer();
      }
      return this;
    };
  
    prototype$1m.tooltip = function(handler) {
      if (!arguments.length) return this._tooltip;
      if (handler !== this._tooltip) {
        this._tooltip = handler;
        this._resetRenderer();
      }
      return this;
    };
  
    prototype$1m.loader = function(loader) {
      if (!arguments.length) return this._loader;
      if (loader !== this._loader) {
        Dataflow.prototype.loader.call(this, loader);
        this._resetRenderer();
      }
      return this;
    };
  
    prototype$1m.resize = function() {
      // set flag to perform autosize
      this._autosize = 1;
      // touch autosize signal to ensure top-level ViewLayout runs
      return this.touch(lookupSignal(this, 'autosize'));
    };
  
    prototype$1m._resetRenderer = function() {
      if (this._renderer) {
        this._renderer = null;
        this.initialize(this._el, this._elBind);
      }
    };
  
    // -- SIZING ----
    prototype$1m._resizeView = resizeView;
  
    // -- EVENT HANDLING ----
  
    prototype$1m.addEventListener = function(type, handler, options) {
      var callback = handler;
      if (!(options && options.trap === false)) {
        // wrap callback in error handler
        callback = trap(this, handler);
        callback.raw = handler;
      }
      this._handler.on(type, callback);
      return this;
    };
  
    prototype$1m.removeEventListener = function(type, handler) {
      var handlers = this._handler.handlers(type),
          i = handlers.length, h, t;
  
      // search registered handlers, remove if match found
      while (--i >= 0) {
        t = handlers[i].type;
        h = handlers[i].handler;
        if (type === t && (handler === h || handler === h.raw)) {
          this._handler.off(t, h);
          break;
        }
      }
      return this;
    };
  
    prototype$1m.addResizeListener = function(handler) {
      var l = this._resizeListeners;
      if (l.indexOf(handler) < 0) {
        // add handler if it isn't already registered
        // note: error trapping handled elsewhere, so
        // no need to wrap handlers here
        l.push(handler);
      }
      return this;
    };
  
    prototype$1m.removeResizeListener = function(handler) {
      var l = this._resizeListeners,
          i = l.indexOf(handler);
      if (i >= 0) {
        l.splice(i, 1);
      }
      return this;
    };
  
    function findOperatorHandler(op, handler) {
      var t = op._targets || [],
          h = t.filter(function(op) {
                var u = op._update;
                return u && u.handler === handler;
              });
      return h.length ? h[0] : null;
    }
  
    function addOperatorListener(view, name, op, handler) {
      var h = findOperatorHandler(op, handler);
      if (!h) {
        h = trap(this, function() { handler(name, op.value); });
        h.handler = handler;
        view.on(op, null, h);
      }
      return view;
    }
  
    function removeOperatorListener(view, op, handler) {
      var h = findOperatorHandler(op, handler);
      if (h) op._targets.remove(h);
      return view;
    }
  
    prototype$1m.addSignalListener = function(name, handler) {
      return addOperatorListener(this, name, lookupSignal(this, name), handler);
    };
  
    prototype$1m.removeSignalListener = function(name, handler) {
      return removeOperatorListener(this, lookupSignal(this, name), handler);
    };
  
    prototype$1m.addDataListener = function(name, handler) {
      return addOperatorListener(this, name, dataref(this, name).values, handler);
    };
  
    prototype$1m.removeDataListener = function(name, handler) {
      return removeOperatorListener(this, dataref(this, name).values, handler);
    };
  
    prototype$1m.preventDefault = function(_) {
      if (arguments.length) {
        this._preventDefault = _;
        return this;
      } else {
        return this._preventDefault;
      }
    };
  
    prototype$1m.timer = timer;
    prototype$1m.events = events$1;
    prototype$1m.finalize = finalize;
    prototype$1m.hover = hover;
  
    // -- DATA ----
    prototype$1m.data = data;
    prototype$1m.change = change;
    prototype$1m.insert = insert;
    prototype$1m.remove = remove;
  
    // -- SCALES --
    prototype$1m.scale = scale$3;
  
    // -- INITIALIZATION ----
    prototype$1m.initialize = initialize$1;
  
    // -- HEADLESS RENDERING ----
    prototype$1m.toImageURL = renderToImageURL;
    prototype$1m.toCanvas = renderToCanvas;
    prototype$1m.toSVG = renderToSVG;
  
    // -- SAVE / RESTORE STATE ----
    prototype$1m.getState = getState$1;
    prototype$1m.setState = setState$1;
  
    function parseAutosize(spec, config) {
      spec = spec || config.autosize;
      return isObject(spec)
        ? spec
        : {type: spec || 'pad'};
    }
  
    function parsePadding(spec, config) {
      spec = spec || config.padding;
      return isObject(spec)
        ? {
            top:    number(spec.top),
            bottom: number(spec.bottom),
            left:   number(spec.left),
            right:  number(spec.right)
          }
        : paddingObject(number(spec));
    }
  
    function number(_) {
      return +_ || 0;
    }
  
    function paddingObject(_) {
      return {top: _, bottom: _, left: _, right: _};
    }
  
    var OUTER = 'outer',
        OUTER_INVALID = ['value', 'update', 'init', 'react', 'bind'];
  
    function outerError(prefix, name) {
      error(prefix + ' for "outer" push: ' + $(name));
    }
  
    function parseSignal(signal, scope) {
      var name = signal.name;
  
      if (signal.push === OUTER) {
        // signal must already be defined, raise error if not
        if (!scope.signals[name]) outerError('No prior signal definition', name);
        // signal push must not use properties reserved for standard definition
        OUTER_INVALID.forEach(function(prop) {
          if (signal[prop] !== undefined) outerError('Invalid property ', prop);
        });
      } else {
        // define a new signal in the current scope
        var op = scope.addSignal(name, signal.value);
        if (signal.react === false) op.react = false;
        if (signal.bind) scope.addBinding(name, signal.bind);
      }
    }
  
    function parseExpression$1(expr, scope, preamble) {
      var params = {}, ast, gen;
  
      // parse the expression to an abstract syntax tree (ast)
      try {
        expr = isString(expr) ? expr : ($(expr) + '');
        ast = parse$3(expr);
      } catch (err) {
        error('Expression parse error: ' + expr);
      }
  
      // analyze ast function calls for dependencies
      ast.visit(function visitor(node) {
        if (node.type !== CallExpression) return;
        var name = node.callee.name,
            visit = codegenParams.visitors[name];
        if (visit) visit(name, node.arguments, scope, params);
      });
  
      // perform code generation
      gen = codeGenerator(ast);
  
      // collect signal dependencies
      gen.globals.forEach(function(name) {
        var signalName = SignalPrefix + name;
        if (!params.hasOwnProperty(signalName) && scope.getSignal(name)) {
          params[signalName] = scope.signalRef(name);
        }
      });
  
      // return generated expression code and dependencies
      return {
        $expr:   preamble ? preamble + 'return(' + gen.code + ');' : gen.code,
        $fields: gen.fields,
        $params: params
      };
    }
  
    function Entry(type, value, params, parent) {
      this.id = -1;
      this.type = type;
      this.value = value;
      this.params = params;
      if (parent) this.parent = parent;
    }
  
    function entry(type, value, params, parent) {
      return new Entry(type, value, params, parent);
    }
  
    function operator(value, params) {
      return entry('operator', value, params);
    }
  
    // -----
  
    function ref(op) {
      var ref = {$ref: op.id};
      // if operator not yet registered, cache ref to resolve later
      if (op.id < 0) (op.refs = op.refs || []).push(ref);
      return ref;
    }
  
    var tupleidRef = {
      $tupleid: 1,
      toString: function() { return ':_tupleid_:'; }
    };
  
    function fieldRef(field, name) {
      return name ? {$field: field, $name: name} : {$field: field};
    }
  
    var keyFieldRef = fieldRef('key');
  
    function compareRef(fields, orders) {
      return {$compare: fields, $order: orders};
    }
  
    function keyRef(fields, flat) {
      var ref = {$key: fields};
      if (flat) ref.$flat = true;
      return ref;
    }
  
    // -----
  
    var Ascending  = 'ascending';
  
    var Descending = 'descending';
  
    function sortKey(sort) {
      return !isObject(sort) ? ''
        : (sort.order === Descending ? '-' : '+')
          + aggrField(sort.op, sort.field);
    }
  
    function aggrField(op, field) {
      return (op && op.signal ? '$' + op.signal : op || '')
        + (op && field ? '_' : '')
        + (field && field.signal ? '$' + field.signal : field || '');
    }
  
    // -----
  
    var Scope = 'scope';
  
    var View$1 = 'view';
  
    function isSignal(_) {
      return _ && _.signal;
    }
  
    function isExpr(_) {
      return _ && _.expr;
    }
  
    function hasSignal(_) {
      if (isSignal(_)) return true;
      if (isObject(_)) for (var key in _) {
        if (hasSignal(_[key])) return true;
      }
      return false;
    }
  
    function value(specValue, defaultValue) {
      return specValue != null ? specValue : defaultValue;
    }
  
    function deref(v) {
      return v && v.signal || v;
    }
  
    var Timer = 'timer';
  
    function parseStream$1(stream, scope) {
      var method = stream.merge ? mergeStream
        : stream.stream ? nestedStream
        : stream.type ? eventStream
        : error('Invalid stream specification: ' + $(stream));
  
      return method(stream, scope);
    }
  
    function eventSource(source) {
       return source === Scope ? View$1 : (source || View$1);
    }
  
    function mergeStream(stream, scope) {
      var list = stream.merge.map(s => parseStream$1(s, scope)),
          entry = streamParameters({merge: list}, stream, scope);
      return scope.addStream(entry).id;
    }
  
    function nestedStream(stream, scope) {
      var id = parseStream$1(stream.stream, scope),
          entry = streamParameters({stream: id}, stream, scope);
      return scope.addStream(entry).id;
    }
  
    function eventStream(stream, scope) {
      var id, entry;
  
      if (stream.type === Timer) {
        id = scope.event(Timer, stream.throttle);
        stream = {between: stream.between, filter: stream.filter};
      } else {
        id = scope.event(eventSource(stream.source), stream.type);
      }
  
      entry = streamParameters({stream: id}, stream, scope);
      return Object.keys(entry).length === 1
        ? id
        : scope.addStream(entry).id;
    }
  
    function streamParameters(entry, stream, scope) {
      var param = stream.between;
  
      if (param) {
        if (param.length !== 2) {
          error('Stream "between" parameter must have 2 entries: ' + $(stream));
        }
        entry.between = [
          parseStream$1(param[0], scope),
          parseStream$1(param[1], scope)
        ];
      }
  
      param = stream.filter ? [].concat(stream.filter) : [];
      if (stream.marktype || stream.markname || stream.markrole) {
        // add filter for mark type, name and/or role
        param.push(filterMark(stream.marktype, stream.markname, stream.markrole));
      }
      if (stream.source === Scope) {
        // add filter to limit events from sub-scope only
        param.push('inScope(event.item)');
      }
      if (param.length) {
        entry.filter = parseExpression$1('(' + param.join(')&&(') + ')').$expr;
      }
  
      if ((param = stream.throttle) != null) {
        entry.throttle = +param;
      }
  
      if ((param = stream.debounce) != null) {
        entry.debounce = +param;
      }
  
      if (stream.consume) {
        entry.consume = true;
      }
  
      return entry;
    }
  
    function filterMark(type, name, role) {
      var item = 'event.item';
      return item
        + (type && type !== '*' ? '&&' + item + '.mark.marktype===\'' + type + '\'' : '')
        + (role ? '&&' + item + '.mark.role===\'' + role + '\'' : '')
        + (name ? '&&' + item + '.mark.name===\'' + name + '\'' : '');
    }
  
    /**
     * Parse an event selector string.
     * Returns an array of event stream definitions.
     */
    function selector(selector, source, marks) {
      DEFAULT_SOURCE = source || VIEW$1;
      MARKS = marks || DEFAULT_MARKS;
      return parseMerge(selector.trim()).map(parseSelector);
    }
  
    var VIEW$1    = 'view',
        LBRACK  = '[',
        RBRACK  = ']',
        LBRACE  = '{',
        RBRACE  = '}',
        COLON   = ':',
        COMMA   = ',',
        NAME    = '@',
        GT      = '>',
        ILLEGAL$1 = /[[\]{}]/,
        DEFAULT_SOURCE,
        MARKS,
        DEFAULT_MARKS = {
          '*': 1,
          arc: 1,
          area: 1,
          group: 1,
          image: 1,
          line: 1,
          path: 1,
          rect: 1,
          rule: 1,
          shape: 1,
          symbol: 1,
          text: 1,
          trail: 1
        };
  
    function isMarkType(type) {
      return MARKS.hasOwnProperty(type);
    }
  
    function find$1(s, i, endChar, pushChar, popChar) {
      var count = 0,
          n = s.length,
          c;
      for (; i<n; ++i) {
        c = s[i];
        if (!count && c === endChar) return i;
        else if (popChar && popChar.indexOf(c) >= 0) --count;
        else if (pushChar && pushChar.indexOf(c) >= 0) ++count;
      }
      return i;
    }
  
    function parseMerge(s) {
      var output = [],
          start = 0,
          n = s.length,
          i = 0;
  
      while (i < n) {
        i = find$1(s, i, COMMA, LBRACK + LBRACE, RBRACK + RBRACE);
        output.push(s.substring(start, i).trim());
        start = ++i;
      }
  
      if (output.length === 0) {
        throw 'Empty event selector: ' + s;
      }
      return output;
    }
  
    function parseSelector(s) {
      return s[0] === '['
        ? parseBetween(s)
        : parseStream$2(s);
    }
  
    function parseBetween(s) {
      var n = s.length,
          i = 1,
          b, stream;
  
      i = find$1(s, i, RBRACK, LBRACK, RBRACK);
      if (i === n) {
        throw 'Empty between selector: ' + s;
      }
  
      b = parseMerge(s.substring(1, i));
      if (b.length !== 2) {
        throw 'Between selector must have two elements: ' + s;
      }
  
      s = s.slice(i + 1).trim();
      if (s[0] !== GT) {
        throw 'Expected \'>\' after between selector: ' + s;
      }
  
      b = b.map(parseSelector);
  
      stream = parseSelector(s.slice(1).trim());
      if (stream.between) {
        return {
          between: b,
          stream: stream
        };
      } else {
        stream.between = b;
      }
  
      return stream;
    }
  
    function parseStream$2(s) {
      var stream = {source: DEFAULT_SOURCE},
          source = [],
          throttle = [0, 0],
          markname = 0,
          start = 0,
          n = s.length,
          i = 0, j,
          filter;
  
      // extract throttle from end
      if (s[n-1] === RBRACE) {
        i = s.lastIndexOf(LBRACE);
        if (i >= 0) {
          try {
            throttle = parseThrottle(s.substring(i+1, n-1));
          } catch (e) {
            throw 'Invalid throttle specification: ' + s;
          }
          s = s.slice(0, i).trim();
          n = s.length;
        } else throw 'Unmatched right brace: ' + s;
        i = 0;
      }
  
      if (!n) throw s;
  
      // set name flag based on first char
      if (s[0] === NAME) markname = ++i;
  
      // extract first part of multi-part stream selector
      j = find$1(s, i, COLON);
      if (j < n) {
        source.push(s.substring(start, j).trim());
        start = i = ++j;
      }
  
      // extract remaining part of stream selector
      i = find$1(s, i, LBRACK);
      if (i === n) {
        source.push(s.substring(start, n).trim());
      } else {
        source.push(s.substring(start, i).trim());
        filter = [];
        start = ++i;
        if (start === n) throw 'Unmatched left bracket: ' + s;
      }
  
      // extract filters
      while (i < n) {
        i = find$1(s, i, RBRACK);
        if (i === n) throw 'Unmatched left bracket: ' + s;
        filter.push(s.substring(start, i).trim());
        if (i < n-1 && s[++i] !== LBRACK) throw 'Expected left bracket: ' + s;
        start = ++i;
      }
  
      // marshall event stream specification
      if (!(n = source.length) || ILLEGAL$1.test(source[n-1])) {
        throw 'Invalid event selector: ' + s;
      }
  
      if (n > 1) {
        stream.type = source[1];
        if (markname) {
          stream.markname = source[0].slice(1);
        } else if (isMarkType(source[0])) {
          stream.marktype = source[0];
        } else {
          stream.source = source[0];
        }
      } else {
        stream.type = source[0];
      }
      if (stream.type.slice(-1) === '!') {
        stream.consume = true;
        stream.type = stream.type.slice(0, -1);
      }
      if (filter != null) stream.filter = filter;
      if (throttle[0]) stream.throttle = throttle[0];
      if (throttle[1]) stream.debounce = throttle[1];
  
      return stream;
    }
  
    function parseThrottle(s) {
      var a = s.split(COMMA);
      if (!s.length || a.length > 2) throw s;
      return a.map(function(_) {
        var x = +_;
        if (x !== x) throw s;
        return x;
      });
    }
  
    var preamble = 'var datum=event.item&&event.item.datum;';
  
    function parseUpdate$1(spec, scope, target) {
      var events = spec.events,
          update = spec.update,
          encode = spec.encode,
          sources = [],
          entry = {target: target};
  
      if (!events) {
        error('Signal update missing events specification.');
      }
  
      // interpret as an event selector string
      if (isString(events)) {
        events = selector(events, scope.isSubscope() ? Scope : View$1);
      }
  
      // separate event streams from signal updates
      events = array(events)
        .filter(s => s.signal || s.scale ? (sources.push(s), 0) : 1);
  
      // merge internal operator listeners
      if (sources.length > 1) {
        sources = [mergeSources(sources)];
      }
  
      // merge event streams, include as source
      if (events.length) {
        sources.push(events.length > 1 ? {merge: events} : events[0]);
      }
  
      if (encode != null) {
        if (update) error('Signal encode and update are mutually exclusive.');
        update = 'encode(item(),' + $(encode) + ')';
      }
  
      // resolve update value
      entry.update = isString(update) ? parseExpression$1(update, scope, preamble)
        : update.expr != null ? parseExpression$1(update.expr, scope, preamble)
        : update.value != null ? update.value
        : update.signal != null ? {
            $expr:   '_.value',
            $params: {value: scope.signalRef(update.signal)}
          }
        : error('Invalid signal update specification.');
  
      if (spec.force) {
        entry.options = {force: true};
      }
  
      sources.forEach(function(source) {
        scope.addUpdate(extend(streamSource(source, scope), entry));
      });
    }
  
    function streamSource(stream, scope) {
      return {
        source: stream.signal ? scope.signalRef(stream.signal)
              : stream.scale ? scope.scaleRef(stream.scale)
              : parseStream$1(stream, scope)
      };
    }
  
    function mergeSources(sources) {
      return {
        signal: '['
          + sources.map(s => s.scale ? 'scale("' + s.scale + '")' : s.signal)
          + ']'
      };
    }
  
    function parseSignalUpdates(signal, scope) {
      var op = scope.getSignal(signal.name),
          expr = signal.update;
  
      if (signal.init) {
        if (expr) {
          error('Signals can not include both init and update expressions.');
        } else {
          expr = signal.init;
          op.initonly = true;
        }
      }
  
      if (expr) {
        expr = parseExpression$1(expr, scope);
        op.update = expr.$expr;
        op.params = expr.$params;
      }
  
      if (signal.on) {
        signal.on.forEach(function(_) {
          parseUpdate$1(_, scope, op.id);
        });
      }
    }
  
    function transform$1(name) {
      return function(params, value, parent) {
        return entry(name, value, params || undefined, parent);
      };
    }
  
    var Aggregate$1 = transform$1('aggregate');
    var AxisTicks$1 = transform$1('axisticks');
    var Bound$1 = transform$1('bound');
    var Collect$1 = transform$1('collect');
    var Compare$1 = transform$1('compare');
    var DataJoin$1 = transform$1('datajoin');
    var Encode$1 = transform$1('encode');
    var Expression$1 = transform$1('expression');
    var Facet$1 = transform$1('facet');
    var Field$1 = transform$1('field');
    var Key$1 = transform$1('key');
    var LegendEntries$1 = transform$1('legendentries');
    var Load$1 = transform$1('load');
    var Mark$1 = transform$1('mark');
    var MultiExtent$1 = transform$1('multiextent');
    var MultiValues$1 = transform$1('multivalues');
    var Overlap$1 = transform$1('overlap');
    var Params$2 = transform$1('params');
    var PreFacet$1 = transform$1('prefacet');
    var Projection$1 = transform$1('projection');
    var Proxy$1 = transform$1('proxy');
    var Relay$1 = transform$1('relay');
    var Render$1 = transform$1('render');
    var Scale$1 = transform$1('scale');
    var Sieve$1 = transform$1('sieve');
    var SortItems$1 = transform$1('sortitems');
    var ViewLayout$1 = transform$1('viewlayout');
    var Values$1 = transform$1('values');
  
    var FIELD_REF_ID = 0;
  
    function initScale(spec, scope) {
      var type = spec.type || 'linear';
  
      if (!isValidScaleType(type)) {
        error('Unrecognized scale type: ' + $(type));
      }
  
      scope.addScale(spec.name, {
        type:   type,
        domain: undefined
      });
    }
  
    function parseScale(spec, scope) {
      var params = scope.getScale(spec.name).params,
          key;
  
      params.domain = parseScaleDomain(spec.domain, spec, scope);
  
      if (spec.range != null) {
        params.range = parseScaleRange(spec, scope, params);
      }
  
      if (spec.interpolate != null) {
        parseScaleInterpolate(spec.interpolate, params);
      }
  
      if (spec.nice != null) {
        params.nice = parseScaleNice(spec.nice);
      }
  
      if (spec.bins != null) {
        params.bins = parseScaleBins(spec.bins, scope);
      }
  
      for (key in spec) {
        if (params.hasOwnProperty(key) || key === 'name') continue;
        params[key] = parseLiteral(spec[key], scope);
      }
    }
  
    function parseLiteral(v, scope) {
      return !isObject(v) ? v
        : v.signal ? scope.signalRef(v.signal)
        : error('Unsupported object: ' + $(v));
    }
  
    function parseArray(v, scope) {
      return v.signal
        ? scope.signalRef(v.signal)
        : v.map(v => parseLiteral(v, scope));
    }
  
    function dataLookupError(name) {
      error('Can not find data set: ' + $(name));
    }
  
    // -- SCALE DOMAIN ----
  
    function parseScaleDomain(domain, spec, scope) {
      if (!domain) {
        if (spec.domainMin != null || spec.domainMax != null) {
          error('No scale domain defined for domainMin/domainMax to override.');
        }
        return; // default domain
      }
  
      return domain.signal ? scope.signalRef(domain.signal)
        : (isArray(domain) ? explicitDomain
        : domain.fields ? multipleDomain
        : singularDomain)(domain, spec, scope);
    }
  
    function explicitDomain(domain, spec, scope) {
      return domain.map(function(v) {
        return parseLiteral(v, scope);
      });
    }
  
    function singularDomain(domain, spec, scope) {
      var data = scope.getData(domain.data);
      if (!data) dataLookupError(domain.data);
  
      return isDiscrete(spec.type)
          ? data.valuesRef(scope, domain.field, parseSort(domain.sort, false))
          : isQuantile(spec.type) ? data.domainRef(scope, domain.field)
          : data.extentRef(scope, domain.field);
    }
  
    function multipleDomain(domain, spec, scope) {
      var data = domain.data,
          fields = domain.fields.reduce(function(dom, d) {
            d = isString(d) ? {data: data, field: d}
              : (isArray(d) || d.signal) ? fieldRef$1(d, scope)
              : d;
            dom.push(d);
            return dom;
          }, []);
  
      return (isDiscrete(spec.type) ? ordinalMultipleDomain
        : isQuantile(spec.type) ? quantileMultipleDomain
        : numericMultipleDomain)(domain, scope, fields);
    }
  
    function fieldRef$1(data, scope) {
      var name = '_:vega:_' + (FIELD_REF_ID++),
          coll = Collect$1({});
  
      if (isArray(data)) {
        coll.value = {$ingest: data};
      } else if (data.signal) {
        var code = 'setdata(' + $(name) + ',' + data.signal + ')';
        coll.params.input = scope.signalRef(code);
      }
      scope.addDataPipeline(name, [coll, Sieve$1({})]);
      return {data: name, field: 'data'};
    }
  
    function ordinalMultipleDomain(domain, scope, fields) {
      var counts, a, c, v;
  
      // get value counts for each domain field
      counts = fields.map(function(f) {
        var data = scope.getData(f.data);
        if (!data) dataLookupError(f.data);
        return data.countsRef(scope, f.field);
      });
  
      // sum counts from all fields
      a = scope.add(Aggregate$1({
        groupby: keyFieldRef,
        ops:['sum'], fields: [scope.fieldRef('count')], as:['count'],
        pulse: counts
      }));
  
      // collect aggregate output
      c = scope.add(Collect$1({pulse: ref(a)}));
  
      // extract values for combined domain
      v = scope.add(Values$1({
        field: keyFieldRef,
        sort:  scope.sortRef(parseSort(domain.sort, true)),
        pulse: ref(c)
      }));
  
      return ref(v);
    }
  
    function parseSort(sort, multidomain) {
      if (sort) {
        if (!sort.field && !sort.op) {
          if (isObject(sort)) sort.field = 'key';
          else sort = {field: 'key'};
        } else if (!sort.field && sort.op !== 'count') {
          error('No field provided for sort aggregate op: ' + sort.op);
        } else if (multidomain && sort.field) {
          error('Multiple domain scales can not sort by field.');
        } else if (multidomain && sort.op && sort.op !== 'count') {
          error('Multiple domain scales support op count only.');
        }
      }
      return sort;
    }
  
    function quantileMultipleDomain(domain, scope, fields) {
      // get value arrays for each domain field
      var values = fields.map(function(f) {
        var data = scope.getData(f.data);
        if (!data) dataLookupError(f.data);
        return data.domainRef(scope, f.field);
      });
  
      // combine value arrays
      return ref(scope.add(MultiValues$1({values: values})));
    }
  
    function numericMultipleDomain(domain, scope, fields) {
      // get extents for each domain field
      var extents = fields.map(function(f) {
        var data = scope.getData(f.data);
        if (!data) dataLookupError(f.data);
        return data.extentRef(scope, f.field);
      });
  
      // combine extents
      return ref(scope.add(MultiExtent$1({extents: extents})));
    }
  
    // -- SCALE BINS -----
  
    function parseScaleBins(v, scope) {
      return v.signal || isArray(v)
        ? parseArray(v, scope)
        : scope.objectProperty(v);
    }
  
    // -- SCALE NICE -----
  
    function parseScaleNice(nice) {
      return isObject(nice)
        ? {
            interval: parseLiteral(nice.interval),
            step: parseLiteral(nice.step)
          }
        : parseLiteral(nice);
    }
  
    // -- SCALE INTERPOLATION -----
  
    function parseScaleInterpolate(interpolate, params) {
      params.interpolate = parseLiteral(interpolate.type || interpolate);
      if (interpolate.gamma != null) {
        params.interpolateGamma = parseLiteral(interpolate.gamma);
      }
    }
  
    // -- SCALE RANGE -----
  
    function parseScaleRange(spec, scope, params) {
      var range = spec.range,
          config = scope.config.range;
  
      if (range.signal) {
        return scope.signalRef(range.signal);
      } else if (isString(range)) {
        if (config && config.hasOwnProperty(range)) {
          spec = extend({}, spec, {range: config[range]});
          return parseScaleRange(spec, scope, params);
        } else if (range === 'width') {
          range = [0, {signal: 'width'}];
        } else if (range === 'height') {
          range = isDiscrete(spec.type)
            ? [0, {signal: 'height'}]
            : [{signal: 'height'}, 0];
        } else {
          error('Unrecognized scale range value: ' + $(range));
        }
      } else if (range.scheme) {
        params.scheme = isArray(range.scheme)
          ? parseArray(range.scheme, scope)
          : parseLiteral(range.scheme, scope);
        if (range.extent) params.schemeExtent = parseArray(range.extent, scope);
        if (range.count) params.schemeCount = parseLiteral(range.count, scope);
        return;
      } else if (range.step) {
        params.rangeStep = parseLiteral(range.step, scope);
        return;
      } else if (isDiscrete(spec.type) && !isArray(range)) {
        return parseScaleDomain(range, spec, scope);
      } else if (!isArray(range)) {
        error('Unsupported range type: ' + $(range));
      }
  
      return range.map(v => (isArray(v) ? parseArray : parseLiteral)(v, scope));
    }
  
    function parseProjection(proj, scope) {
      var params = {};
  
      for (var name in proj) {
        if (name === 'name') continue;
        params[name] = parseParameter$1(proj[name], name, scope);
      }
  
      scope.addProjection(proj.name, params);
    }
  
    function parseParameter$1(_, name, scope) {
      return isArray(_) ? _.map(function(_) { return parseParameter$1(_, name, scope); })
        : !isObject(_) ? _
        : _.signal ? scope.signalRef(_.signal)
        : name === 'fit' ? _
        : error('Unsupported parameter object: ' + $(_));
    }
  
    const Top$1 = 'top';
    const Left$1 = 'left';
    const Right$1 = 'right';
    const Bottom$1 = 'bottom';
    const Center$1 = 'center';
  
    const Vertical = 'vertical';
  
    const Start$1 = 'start';
    const Middle$1 = 'middle';
    const End$1 = 'end';
  
    const Index  = 'index';
    const Label  = 'label';
    const Offset = 'offset';
    const Perc   = 'perc';
    const Perc2  = 'perc2';
    const Size   = 'size';
    const Value  = 'value';
  
    const GuideLabelStyle = 'guide-label';
    const GuideTitleStyle = 'guide-title';
    const GroupTitleStyle = 'group-title';
  
    const Symbols$2 = 'symbol';
    const Gradient$2 = 'gradient';
    const Discrete$1 = 'discrete';
  
    // Encoding channels supported by legends
    // In priority order of 'canonical' scale
    const LegendScales = [
      'size',
      'shape',
      'fill',
      'stroke',
      'strokeWidth',
      'strokeDash',
      'opacity'
    ];
  
    const Skip$1 = {
      name: 1,
      interactive: 1
    };
  
    const zero$1 = {value: 0};
    const one$1 = {value: 1};
  
    var Skip$2 = toSet(['rule']),
        Swap = toSet(['group', 'image', 'rect']);
  
    function adjustSpatial(encode, marktype) {
      var code = '';
  
      if (Skip$2[marktype]) return code;
  
      if (encode.x2) {
        if (encode.x) {
          if (Swap[marktype]) {
            code += 'if(o.x>o.x2)$=o.x,o.x=o.x2,o.x2=$;';
          }
          code += 'o.width=o.x2-o.x;';
        } else {
          code += 'o.x=o.x2-(o.width||0);';
        }
      }
  
      if (encode.xc) {
        code += 'o.x=o.xc-(o.width||0)/2;';
      }
  
      if (encode.y2) {
        if (encode.y) {
          if (Swap[marktype]) {
            code += 'if(o.y>o.y2)$=o.y,o.y=o.y2,o.y2=$;';
          }
          code += 'o.height=o.y2-o.y;';
        } else {
          code += 'o.y=o.y2-(o.height||0);';
        }
      }
  
      if (encode.yc) {
        code += 'o.y=o.yc-(o.height||0)/2;';
      }
  
      return code;
    }
  
    function color$1(enc, scope, params, fields) {
      function color(type, x, y, z) {
        var a = entry$1(null, x, scope, params, fields),
            b = entry$1(null, y, scope, params, fields),
            c = entry$1(null, z, scope, params, fields);
        return 'this.' + type + '(' + [a, b, c].join(',') + ').toString()';
      }
  
      return (enc.c) ? color('hcl', enc.h, enc.c, enc.l)
        : (enc.h || enc.s) ? color('hsl', enc.h, enc.s, enc.l)
        : (enc.l || enc.a) ? color('lab', enc.l, enc.a, enc.b)
        : (enc.r || enc.g || enc.b) ? color('rgb', enc.r, enc.g, enc.b)
        : null;
    }
  
    function expression$1(code, scope, params, fields) {
      var expr = parseExpression$1(code, scope);
      expr.$fields.forEach(function(name) { fields[name] = 1; });
      extend(params, expr.$params);
      return expr.$expr;
    }
  
    function field$1(ref, scope, params, fields) {
      return resolve$1(isObject(ref) ? ref : {datum: ref}, scope, params, fields);
    }
  
    function resolve$1(ref, scope, params, fields) {
      var object, level, field;
  
      if (ref.signal) {
        object = 'datum';
        field = expression$1(ref.signal, scope, params, fields);
      } else if (ref.group || ref.parent) {
        level = Math.max(1, ref.level || 1);
        object = 'item';
  
        while (level-- > 0) {
          object += '.mark.group';
        }
  
        if (ref.parent) {
          field = ref.parent;
          object += '.datum';
        } else {
          field = ref.group;
        }
      } else if (ref.datum) {
        object = 'datum';
        field = ref.datum;
      } else {
        error('Invalid field reference: ' + $(ref));
      }
  
      if (!ref.signal) {
        if (isString(field)) {
          fields[field] = 1; // TODO review field tracking?
          field = splitAccessPath(field).map($).join('][');
        } else {
          field = resolve$1(field, scope, params, fields);
        }
      }
  
      return object + '[' + field + ']';
    }
  
    function scale$4(enc, value, scope, params, fields) {
      var scale = getScale$1(enc.scale, scope, params, fields),
          interp, func, flag;
  
      if (enc.range != null) {
        // pull value from scale range
        interp = +enc.range;
        func = scale + '.range()';
        value = (interp === 0) ? (func + '[0]')
          : '($=' + func + ',' + ((interp === 1) ? '$[$.length-1]'
          : '$[0]+' + interp + '*($[$.length-1]-$[0])') + ')';
      } else {
        // run value through scale and/or pull scale bandwidth
        if (value !== undefined) value = scale + '(' + value + ')';
  
        if (enc.band && (flag = hasBandwidth(enc.scale, scope))) {
          func = scale + '.bandwidth';
          interp = +enc.band;
          interp = func + '()' + (interp===1 ? '' : '*' + interp);
  
          // if we don't know the scale type, check for bandwidth
          if (flag < 0) interp = '(' + func + '?' + interp + ':0)';
  
          value = (value ? value + '+' : '') + interp;
  
          if (enc.extra) {
            // include logic to handle extraneous elements
            value = '(datum.extra?' + scale + '(datum.extra.value):' + value + ')';
          }
        }
  
        if (value == null) value = '0';
      }
  
      return value;
    }
  
    function hasBandwidth(name, scope) {
      if (!isString(name)) return -1;
      var type = scope.scaleType(name);
      return type === 'band' || type === 'point' ? 1 : 0;
    }
  
    function getScale$1(name, scope, params, fields) {
      var scaleName;
  
      if (isString(name)) {
        // direct scale lookup; add scale as parameter
        scaleName = ScalePrefix + name;
        if (!params.hasOwnProperty(scaleName)) {
          params[scaleName] = scope.scaleRef(name);
        }
        scaleName = $(scaleName);
      } else {
        // indirect scale lookup; add all scales as parameters
        for (scaleName in scope.scales) {
          params[ScalePrefix + scaleName] = scope.scaleRef(scaleName);
        }
        scaleName = $(ScalePrefix) + '+'
          + (name.signal
            ? '(' + expression$1(name.signal, scope, params, fields) + ')'
            : field$1(name, scope, params, fields));
      }
  
      return '_[' + scaleName + ']';
    }
  
    function gradient$1(enc, scope, params, fields) {
      return 'this.gradient('
        + getScale$1(enc.gradient, scope, params, fields)
        + ',' + $(enc.start)
        + ',' + $(enc.stop)
        + ',' + $(enc.count)
        + ')';
    }
  
    function property(property, scope, params, fields) {
      return isObject(property)
          ? '(' + entry$1(null, property, scope, params, fields) + ')'
          : property;
    }
  
    function entry$1(channel, enc, scope, params, fields) {
      if (enc.gradient != null) {
        return gradient$1(enc, scope, params, fields);
      }
  
      var value = enc.signal ? expression$1(enc.signal, scope, params, fields)
        : enc.color ? color$1(enc.color, scope, params, fields)
        : enc.field != null ? field$1(enc.field, scope, params, fields)
        : enc.value !== undefined ? $(enc.value)
        : undefined;
  
      if (enc.scale != null) {
        value = scale$4(enc, value, scope, params, fields);
      }
  
      if (value === undefined) {
        value = null;
      }
  
      if (enc.exponent != null) {
        value = 'Math.pow(' + value + ','
          + property(enc.exponent, scope, params, fields) + ')';
      }
  
      if (enc.mult != null) {
        value += '*' + property(enc.mult, scope, params, fields);
      }
  
      if (enc.offset != null) {
        value += '+' + property(enc.offset, scope, params, fields);
      }
  
      if (enc.round) {
        value = 'Math.round(' + value + ')';
      }
  
      return value;
    }
  
    function set$2(obj, key, value) {
      const o = obj + '[' + $(key) + ']';
      return `$=${value};if(${o}!==$)${o}=$,m=1;`;
    }
  
    function rule$1(channel, rules, scope, params, fields) {
      var code = '';
  
      rules.forEach(function(rule) {
        var value = entry$1(channel, rule, scope, params, fields);
        code += rule.test
          ? expression$1(rule.test, scope, params, fields) + '?' + value + ':'
          : value;
      });
  
      // if no else clause, terminate with null (vega/vega#1366)
      if (peek(code) === ':') {
        code += 'null';
      }
  
      return set$2('o', channel, code);
    }
  
    function parseEncode(encode, marktype, params, scope) {
      var fields = {},
          code = 'var o=item,datum=o.datum,m=0,$;',
          channel, enc, value;
  
      for (channel in encode) {
        enc = encode[channel];
        if (isArray(enc)) { // rule
          code += rule$1(channel, enc, scope, params, fields);
        } else {
          value = entry$1(channel, enc, scope, params, fields);
          code += set$2('o', channel, value);
        }
      }
  
      code += adjustSpatial(encode, marktype);
      code += 'return m;';
  
      return {
        $expr:   code,
        $fields: Object.keys(fields),
        $output: Object.keys(encode)
      };
    }
  
    var MarkRole = 'mark';
    var FrameRole$1 = 'frame';
    var ScopeRole$1 = 'scope';
  
    var AxisRole$1 = 'axis';
    var AxisDomainRole = 'axis-domain';
    var AxisGridRole = 'axis-grid';
    var AxisLabelRole = 'axis-label';
    var AxisTickRole = 'axis-tick';
    var AxisTitleRole = 'axis-title';
  
    var LegendRole$1 = 'legend';
    var LegendBandRole = 'legend-band';
    var LegendEntryRole = 'legend-entry';
    var LegendGradientRole = 'legend-gradient';
    var LegendLabelRole = 'legend-label';
    var LegendSymbolRole = 'legend-symbol';
    var LegendTitleRole = 'legend-title';
  
    var TitleRole$1 = 'title';
  
    function encoder(_) {
      return isObject(_) ? extend({}, _) : {value: _};
    }
  
    function addEncode(object, name, value, set) {
      if (value != null) {
        if (isObject(value) && !isArray(value)) {
          object.update[name] = value;
        } else {
          object[set || 'enter'][name] = {value: value};
        }
        return 1;
      } else {
        return 0;
      }
    }
  
    function addEncoders(object, enter, update) {
      for (let name in enter) {
        addEncode(object, name, enter[name]);
      }
      for (let name in update) {
        addEncode(object, name, update[name], 'update');
      }
    }
  
    function extendEncode(encode, extra, skip) {
      for (var name in extra) {
        if (skip && skip.hasOwnProperty(name)) continue;
        encode[name] = extend(encode[name] || {}, extra[name]);
      }
      return encode;
    }
  
    function encoders(encode, type, role, style, scope, params) {
      var enc, key;
      params = params || {};
      params.encoders = {$encode: (enc = {})};
  
      encode = applyDefaults(encode, type, role, style, scope.config);
  
      for (key in encode) {
        enc[key] = parseEncode(encode[key], type, params, scope);
      }
  
      return params;
    }
  
    function applyDefaults(encode, type, role, style, config) {
      var enter = {}, key, skip, props;
  
      // ignore legend and axis
      if (role == 'legend' || String(role).indexOf('axis') === 0) {
        role = null;
      }
  
      // resolve mark config
      props = role === FrameRole$1 ? config.group
        : (role === MarkRole) ? extend({}, config.mark, config[type])
        : null;
  
      for (key in props) {
        // do not apply defaults if relevant fields are defined
        skip = has(key, encode)
          || (key === 'fill' || key === 'stroke')
          && (has('fill', encode) || has('stroke', encode));
  
        if (!skip) enter[key] = defaultEncode(props[key]);
      }
  
      // resolve styles, apply with increasing precedence
      array(style).forEach(function(name) {
        var props = config.style && config.style[name];
        for (var key in props) {
          if (!has(key, encode)) {
            enter[key] = defaultEncode(props[key]);
          }
        }
      });
  
      encode = extend({}, encode); // defensive copy
      encode.enter = extend(enter, encode.enter);
  
      return encode;
    }
  
    function defaultEncode(value) {
      return value && value.signal
        ? {signal: value.signal}
        : {value: value};
    }
  
    function has(key, encode) {
      return encode && (
        (encode.enter && encode.enter[key]) ||
        (encode.update && encode.update[key])
      );
    }
  
    function guideMark(type, role, style, key, dataRef, encode, extras) {
      return {
        type:  type,
        name:  extras ? extras.name : undefined,
        role:  role,
        style: (extras && extras.style) || style,
        key:   key,
        from:  dataRef,
        interactive: !!(extras && extras.interactive),
        encode: extendEncode(encode, extras, Skip$1)
      };
    }
  
    function lookup$5(spec, config) {
      const _ = name => value(spec[name], config[name]);
  
      _.isVertical = s => Vertical === value(
        spec.direction,
        config.direction || (s ? config.symbolDirection : config.gradientDirection)
      );
  
      _.gradientLength = () => value(
        spec.gradientLength,
        config.gradientLength || config.gradientWidth
      );
  
      _.gradientThickness = () => value(
        spec.gradientThickness,
        config.gradientThickness || config.gradientHeight
      );
  
      _.entryColumns = () => value(
        spec.columns,
        value(config.columns, +_.isVertical(true))
      );
  
      return _;
    }
  
    function getEncoding(name, encode) {
      var v = encode && (
        (encode.update && encode.update[name]) ||
        (encode.enter && encode.enter[name])
      );
      return v && v.signal ? v : v ? v.value : null;
    }
  
    function getStyle(name, scope, style) {
      var s = scope.config.style[style];
      return s && s[name];
    }
  
    function anchorExpr(s, e, m) {
      return `item.anchor === "${Start$1}" ? ${s} : item.anchor === "${End$1}" ? ${e} : ${m}`;
    }
  
    const alignExpr = anchorExpr(
      $(Left$1),
      $(Right$1),
      $(Center$1)
    );
  
    var GroupMark = 'group';
    var RectMark = 'rect';
    var RuleMark = 'rule';
    var SymbolMark = 'symbol';
    var TextMark = 'text';
  
    function legendGradient(spec, scale, config, userEncode) {
      var _ = lookup$5(spec, config),
          vertical = _.isVertical(),
          thickness = _.gradientThickness(),
          length = _.gradientLength(),
          encode, enter, start, stop, width, height;
  
      if (vertical) {
        start = [0, 1];
        stop = [0, 0];
        width = thickness;
        height = length;
      } else {
        start = [0, 0];
        stop = [1, 0];
        width = length;
        height = thickness;
      }
  
      encode = {
        enter: enter = {
          opacity: zero$1,
          x: zero$1,
          y: zero$1,
          width: encoder(width),
          height: encoder(height)
        },
        update: extend({}, enter, {
          opacity: one$1,
          fill: {gradient: scale, start: start, stop: stop}
        }),
        exit: {
          opacity: zero$1
        }
      };
  
      addEncoders(encode, {
        stroke:      _('gradientStrokeColor'),
        strokeWidth: _('gradientStrokeWidth')
      }, { // update
        opacity:     _('gradientOpacity')
      });
  
      return guideMark(RectMark, LegendGradientRole, null, undefined, undefined, encode, userEncode);
    }
  
    function legendGradientDiscrete(spec, scale, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config),
          vertical = _.isVertical(),
          thickness = _.gradientThickness(),
          length = _.gradientLength(),
          encode, enter, u, v, uu, vv, adjust = '';
  
      vertical
        ? (u = 'y', uu = 'y2', v = 'x', vv = 'width', adjust = '1-')
        : (u = 'x', uu = 'x2', v = 'y', vv = 'height');
  
      enter = {
        opacity: zero$1,
        fill: {scale: scale, field: Value}
      };
      enter[u]  = {signal: adjust + 'datum.' + Perc, mult: length};
      enter[v]  = zero$1;
      enter[uu] = {signal: adjust + 'datum.' + Perc2, mult: length};
      enter[vv] = encoder(thickness);
  
      encode = {
        enter: enter,
        update: extend({}, enter, {opacity: one$1}),
        exit: {opacity: zero$1}
      };
  
      addEncoders(encode, {
        stroke:      _('gradientStrokeColor'),
        strokeWidth: _('gradientStrokeWidth')
      }, { // update
        opacity:     _('gradientOpacity')
      });
  
      return guideMark(RectMark, LegendBandRole, null, Value, dataRef, encode, userEncode);
    }
  
    const alignExpr$1 = `datum.${Perc}<=0?"${Left$1}":datum.${Perc}>=1?"${Right$1}":"${Center$1}"`,
          baselineExpr = `datum.${Perc}<=0?"${Bottom$1}":datum.${Perc}>=1?"${Top$1}":"${Middle$1}"`;
  
    function legendGradientLabels(spec, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config),
          vertical = _.isVertical(),
          thickness = encoder(_.gradientThickness()),
          length = _.gradientLength(),
          overlap = _('labelOverlap'),
          separation = _('labelSeparation'),
          encode, enter, update, u, v, adjust = '';
  
      encode = {
        enter: enter = {
          opacity: zero$1
        },
        update: update = {
          opacity: one$1,
          text: {field: Label}
        },
        exit: {
          opacity: zero$1
        }
      };
  
      addEncoders(encode, {
        fill:        _('labelColor'),
        fillOpacity: _('labelOpacity'),
        font:        _('labelFont'),
        fontSize:    _('labelFontSize'),
        fontStyle:   _('labelFontStyle'),
        fontWeight:  _('labelFontWeight'),
        limit:       value(spec.labelLimit, config.gradientLabelLimit)
      });
  
      if (vertical) {
        enter.align = {value: 'left'};
        enter.baseline = update.baseline = {signal: baselineExpr};
        u = 'y'; v = 'x'; adjust = '1-';
      } else {
        enter.align = update.align = {signal: alignExpr$1};
        enter.baseline = {value: 'top'};
        u = 'x'; v = 'y';
      }
  
      enter[u] = update[u] = {signal: adjust + 'datum.' + Perc, mult: length};
  
      enter[v] = update[v] = thickness;
      thickness.offset = value(spec.labelOffset, config.gradientLabelOffset) || 0;
  
      spec = guideMark(TextMark, LegendLabelRole, GuideLabelStyle, Value, dataRef, encode, userEncode);
      if (overlap) {
        spec.overlap = {
          separation: separation,
          method: overlap,
          order: 'datum.' + Index
        };
      }
      return spec;
    }
  
    function guideGroup(role, style, name, dataRef, interactive, encode, marks, layout) {
      return {
        type: GroupMark,
        name: name,
        role: role,
        style: style,
        from: dataRef,
        interactive: interactive || false,
        encode: encode,
        marks: marks,
        layout: layout
      };
    }
  
    // userEncode is top-level, includes entries, symbols, labels
    function legendSymbolGroups(spec, config, userEncode, dataRef, columns) {
      var _ = lookup$5(spec, config),
          entries = userEncode.entries,
          interactive = !!(entries && entries.interactive),
          name = entries ? entries.name : undefined,
          height = _('clipHeight'),
          symbolOffset = _('symbolOffset'),
          valueRef = {data: 'value'},
          encode = {},
          xSignal = `${columns} ? datum.${Offset} : datum.${Size}`,
          yEncode = height ? encoder(height) : {field: Size},
          index = `datum.${Index}`,
          ncols = `max(1, ${columns})`,
          enter, update, labelOffset, symbols, labels, nrows, sort;
  
      yEncode.mult = 0.5;
  
      // -- LEGEND SYMBOLS --
      encode = {
        enter:  enter = {
          opacity: zero$1,
          x: {signal: xSignal, mult: 0.5, offset: symbolOffset},
          y: yEncode
        },
        update: update = {
          opacity: one$1,
          x: enter.x,
          y: enter.y
        },
        exit: {
          opacity: zero$1
        }
      };
  
      if (!spec.fill) {
        addEncoders(encode, {
          fill:   config.symbolBaseFillColor,
          stroke: config.symbolBaseStrokeColor
        });
      }
  
      addEncoders(encode, {
        fill:             _('symbolFillColor'),
        shape:            _('symbolType'),
        size:             _('symbolSize'),
        stroke:           _('symbolStrokeColor'),
        strokeDash:       _('symbolDash'),
        strokeDashOffset: _('symbolDashOffset'),
        strokeWidth:      _('symbolStrokeWidth')
      }, { // update
        opacity:          _('symbolOpacity')
      });
  
      LegendScales.forEach(function(scale) {
        if (spec[scale]) {
          update[scale] = enter[scale] = {scale: spec[scale], field: Value};
        }
      });
  
      symbols = guideMark(
        SymbolMark, LegendSymbolRole, null,
        Value, valueRef, encode, userEncode.symbols
      );
      if (height) symbols.clip = true;
  
      // -- LEGEND LABELS --
      labelOffset = encoder(symbolOffset);
      labelOffset.offset = _('labelOffset');
  
      encode = {
        enter:  enter = {
          opacity: zero$1,
          x: {signal: xSignal, offset: labelOffset},
          y: yEncode
        },
        update: update = {
          opacity: one$1,
          text: {field: Label},
          x: enter.x,
          y: enter.y
        },
        exit: {
          opacity: zero$1
        }
      };
  
      addEncoders(encode, {
        align:       _('labelAlign'),
        baseline:    _('labelBaseline'),
        fill:        _('labelColor'),
        fillOpacity: _('labelOpacity'),
        font:        _('labelFont'),
        fontSize:    _('labelFontSize'),
        fontStyle:   _('labelFontStyle'),
        fontWeight:  _('labelFontWeight'),
        limit:       _('labelLimit')
      });
  
      labels = guideMark(
        TextMark, LegendLabelRole, GuideLabelStyle,
        Value, valueRef, encode, userEncode.labels
      );
  
      // -- LEGEND ENTRY GROUPS --
      encode = {
        enter: {
          noBound: {value: !height}, // ignore width/height in bounds calc
          width: zero$1,
          height: height ? encoder(height) : zero$1,
          opacity: zero$1
        },
        exit: {opacity: zero$1},
        update: update = {
          opacity: one$1,
          row: {signal: null},
          column: {signal: null}
        }
      };
  
      // annotate and sort groups to ensure correct ordering
      if (_.isVertical(true)) {
        nrows = `ceil(item.mark.items.length / ${ncols})`;
        update.row.signal = `${index}%${nrows}`;
        update.column.signal = `floor(${index} / ${nrows})`;
        sort = {field: ['row', index]};
      } else {
        update.row.signal = `floor(${index} / ${ncols})`;
        update.column.signal = `${index} % ${ncols}`;
        sort = {field: index};
      }
      // handle zero column case (implies infinite columns)
      update.column.signal = `${columns}?${update.column.signal}:${index}`;
  
      // facet legend entries into sub-groups
      dataRef = {facet: {data: dataRef, name: 'value', groupby: Index}};
  
      spec = guideGroup(
        ScopeRole$1, null, name, dataRef, interactive,
        extendEncode(encode, entries, Skip$1), [symbols, labels]
      );
      spec.sort = sort;
      return spec;
    }
  
    function legendSymbolLayout(spec, config) {
      const _ = lookup$5(spec, config);
  
      // layout parameters for legend entries
      return {
        align:   _('gridAlign'),
        columns: _.entryColumns(),
        center:  {
          row: true,
          column: false
        },
        padding: {
          row:    _('rowPadding'),
          column: _('columnPadding')
        }
      };
    }
  
    // expression logic for align, anchor, angle, and baseline calculation
    const isL = 'item.orient === "left"',
          isR = 'item.orient === "right"',
          isLR = `(${isL} || ${isR})`,
          isVG = `datum.vgrad && ${isLR}`,
          baseline = anchorExpr('"top"', '"bottom"', '"middle"'),
          alignFlip = anchorExpr('"right"', '"left"', '"center"'),
          exprAlign = `datum.vgrad && ${isR} ? (${alignFlip}) : (${isLR} && !(datum.vgrad && ${isL})) ? "left" : ${alignExpr}`,
          exprAnchor = `item._anchor || (${isLR} ? "middle" : "start")`,
          exprAngle = `${isVG} ? (${isL} ? -90 : 90) : 0`,
          exprBaseline = `${isLR} ? (datum.vgrad ? (${isR} ? "bottom" : "top") : ${baseline}) : "top"`;
  
    function legendTitle(spec, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config), encode;
  
      encode = {
        enter: {opacity: zero$1},
        update: {
          opacity: one$1,
          x: {field: {group: 'padding'}},
          y: {field: {group: 'padding'}}
        },
        exit: {opacity: zero$1}
      };
  
      addEncoders(encode, {
        orient:      _('titleOrient'),
        _anchor:     _('titleAnchor'),
        anchor:      {signal: exprAnchor},
        angle:       {signal: exprAngle},
        align:       {signal: exprAlign},
        baseline:    {signal: exprBaseline},
        text:        spec.title,
        fill:        _('titleColor'),
        fillOpacity: _('titleOpacity'),
        font:        _('titleFont'),
        fontSize:    _('titleFontSize'),
        fontStyle:   _('titleFontStyle'),
        fontWeight:  _('titleFontWeight'),
        limit:       _('titleLimit')
      }, { // require update
        align:       _('titleAlign'),
        baseline:    _('titleBaseline'),
      });
  
      return guideMark(TextMark, LegendTitleRole, GuideTitleStyle, null, dataRef, encode, userEncode);
    }
  
    function clip$2(clip, scope) {
      var expr;
  
      if (isObject(clip)) {
        if (clip.signal) {
          expr = clip.signal;
        } else if (clip.path) {
          expr = 'pathShape(' + param(clip.path) + ')';
        } else if (clip.sphere) {
          expr = 'geoShape(' + param(clip.sphere) + ', {type: "Sphere"})';
        }
      }
  
      return expr
        ? scope.signalRef(expr)
        : !!clip;
    }
  
    function param(value) {
      return isObject(value) && value.signal
        ? value.signal
        : $(value);
    }
  
    function getRole(spec) {
      var role = spec.role || '';
      return (!role.indexOf('axis') || !role.indexOf('legend'))
        ? role
        : spec.type === GroupMark ? ScopeRole$1 : (role || MarkRole);
    }
  
    function definition$1(spec) {
      return {
        marktype:    spec.type,
        name:        spec.name || undefined,
        role:        spec.role || getRole(spec),
        zindex:      +spec.zindex || undefined
      };
    }
  
    function interactive(spec, scope) {
      return spec && spec.signal ? scope.signalRef(spec.signal)
        : spec === false ? false
        : true;
    }
  
    /**
     * Parse a data transform specification.
     */
    function parseTransform(spec, scope) {
      var def = definition(spec.type);
      if (!def) error('Unrecognized transform type: ' + $(spec.type));
  
      var t = entry(def.type.toLowerCase(), null, parseParameters$1(def, spec, scope));
      if (spec.signal) scope.addSignal(spec.signal, scope.proxy(t));
      t.metadata = def.metadata || {};
  
      return t;
    }
  
    /**
     * Parse all parameters of a data transform.
     */
    function parseParameters$1(def, spec, scope) {
      var params = {}, pdef, i, n;
      for (i=0, n=def.params.length; i<n; ++i) {
        pdef = def.params[i];
        params[pdef.name] = parseParameter$2(pdef, spec, scope);
      }
      return params;
    }
  
    /**
     * Parse a data transform parameter.
     */
    function parseParameter$2(def, spec, scope) {
      var type = def.type,
          value = spec[def.name];
  
      if (type === 'index') {
        return parseIndexParameter(def, spec, scope);
      } else if (value === undefined) {
        if (def.required) {
          error('Missing required ' + $(spec.type)
              + ' parameter: ' + $(def.name));
        }
        return;
      } else if (type === 'param') {
        return parseSubParameters(def, spec, scope);
      } else if (type === 'projection') {
        return scope.projectionRef(spec[def.name]);
      }
  
      return def.array && !isSignal(value)
        ? value.map(function(v) { return parameterValue(def, v, scope); })
        : parameterValue(def, value, scope);
    }
  
    /**
     * Parse a single parameter value.
     */
    function parameterValue(def, value, scope) {
      var type = def.type;
  
      if (isSignal(value)) {
        return isExpr$1(type) ? error('Expression references can not be signals.')
             : isField(type) ? scope.fieldRef(value)
             : isCompare(type) ? scope.compareRef(value)
             : scope.signalRef(value.signal);
      } else {
        var expr = def.expr || isField(type);
        return expr && outerExpr(value) ? scope.exprRef(value.expr, value.as)
             : expr && outerField(value) ? fieldRef(value.field, value.as)
             : isExpr$1(type) ? parseExpression$1(value, scope)
             : isData(type) ? ref(scope.getData(value).values)
             : isField(type) ? fieldRef(value)
             : isCompare(type) ? scope.compareRef(value)
             : value;
      }
    }
  
    /**
     * Parse parameter for accessing an index of another data set.
     */
    function parseIndexParameter(def, spec, scope) {
      if (!isString(spec.from)) {
        error('Lookup "from" parameter must be a string literal.');
      }
      return scope.getData(spec.from).lookupRef(scope, spec.key);
    }
  
    /**
     * Parse a parameter that contains one or more sub-parameter objects.
     */
    function parseSubParameters(def, spec, scope) {
      var value = spec[def.name];
  
      if (def.array) {
        if (!isArray(value)) { // signals not allowed!
          error('Expected an array of sub-parameters. Instead: ' + $(value));
        }
        return value.map(function(v) {
          return parseSubParameter(def, v, scope);
        });
      } else {
        return parseSubParameter(def, value, scope);
      }
    }
  
    /**
     * Parse a sub-parameter object.
     */
    function parseSubParameter(def, value, scope) {
      var params, pdef, k, i, n;
  
      // loop over defs to find matching key
      for (i=0, n=def.params.length; i<n; ++i) {
        pdef = def.params[i];
        for (k in pdef.key) {
          if (pdef.key[k] !== value[k]) { pdef = null; break; }
        }
        if (pdef) break;
      }
      // raise error if matching key not found
      if (!pdef) error('Unsupported parameter: ' + $(value));
  
      // parse params, create Params transform, return ref
      params = extend(parseParameters$1(pdef, value, scope), pdef.key);
      return ref(scope.add(Params$2(params)));
    }
  
    // -- Utilities -----
  
    function outerExpr(_) {
      return _ && _.expr;
    }
  
    function outerField(_) {
      return _ && _.field;
    }
  
    function isData(_) {
      return _ === 'data';
    }
  
    function isExpr$1(_) {
      return _ === 'expr';
    }
  
    function isField(_) {
      return _ === 'field';
    }
  
    function isCompare(_) {
      return _ === 'compare'
    }
  
    function parseData(from, group, scope) {
      var facet, key, op, dataRef, parent;
  
      // if no source data, generate singleton datum
      if (!from) {
        dataRef = ref(scope.add(Collect$1(null, [{}])));
      }
  
      // if faceted, process facet specification
      else if (facet = from.facet) {
        if (!group) error('Only group marks can be faceted.');
  
        // use pre-faceted source data, if available
        if (facet.field != null) {
          dataRef = parent = getDataRef(facet, scope);
        } else {
          // generate facet aggregates if no direct data specification
          if (!from.data) {
            op = parseTransform(extend({
              type:    'aggregate',
              groupby: array(facet.groupby)
            }, facet.aggregate), scope);
            op.params.key = scope.keyRef(facet.groupby);
            op.params.pulse = getDataRef(facet, scope);
            dataRef = parent = ref(scope.add(op));
          } else {
            parent = ref(scope.getData(from.data).aggregate);
          }
  
          key = scope.keyRef(facet.groupby, true);
        }
      }
  
      // if not yet defined, get source data reference
      if (!dataRef) {
        dataRef = getDataRef(from, scope);
      }
  
      return {
        key: key,
        pulse: dataRef,
        parent: parent
      };
    }
  
    function getDataRef(from, scope) {
      return from.$ref ? from
        : from.data && from.data.$ref ? from.data
        : ref(scope.getData(from.data).output);
    }
  
    function DataScope(scope, input, output, values, aggr) {
      this.scope = scope;   // parent scope object
      this.input = input;   // first operator in pipeline (tuple input)
      this.output = output; // last operator in pipeline (tuple output)
      this.values = values; // operator for accessing tuples (but not tuple flow)
  
      // last aggregate in transform pipeline
      this.aggregate = aggr;
  
      // lookup table of field indices
      this.index = {};
    }
  
    DataScope.fromEntries = function(scope, entries) {
      var n = entries.length,
          i = 1,
          input  = entries[0],
          values = entries[n-1],
          output = entries[n-2],
          aggr = null;
  
      if (input && input.type === 'load') {
        input = entries[1];
      }
  
      // add operator entries to this scope, wire up pulse chain
      scope.add(entries[0]);
      for (; i<n; ++i) {
        entries[i].params.pulse = ref(entries[i-1]);
        scope.add(entries[i]);
        if (entries[i].type === 'aggregate') aggr = entries[i];
      }
  
      return new DataScope(scope, input, output, values, aggr);
    };
  
    var prototype$1n = DataScope.prototype;
  
    prototype$1n.countsRef = function(scope, field, sort) {
      var ds = this,
          cache = ds.counts || (ds.counts = {}),
          k = fieldKey(field), v, a, p;
  
      if (k != null) {
        scope = ds.scope;
        v = cache[k];
      }
  
      if (!v) {
        p = {
          groupby: scope.fieldRef(field, 'key'),
          pulse: ref(ds.output)
        };
        if (sort && sort.field) addSortField(scope, p, sort);
        a = scope.add(Aggregate$1(p));
        v = scope.add(Collect$1({pulse: ref(a)}));
        v = {agg: a, ref: ref(v)};
        if (k != null) cache[k] = v;
      } else if (sort && sort.field) {
        addSortField(scope, v.agg.params, sort);
      }
  
      return v.ref;
    };
  
    function fieldKey(field) {
      return isString(field) ? field : null;
    }
  
    function addSortField(scope, p, sort) {
      var as = aggrField(sort.op, sort.field), s;
  
      if (p.ops) {
        for (var i=0, n=p.as.length; i<n; ++i) {
          if (p.as[i] === as) return;
        }
      } else {
        p.ops = ['count'];
        p.fields = [null];
        p.as = ['count'];
      }
      if (sort.op) {
        p.ops.push((s=sort.op.signal) ? scope.signalRef(s) : sort.op);
        p.fields.push(scope.fieldRef(sort.field));
        p.as.push(as);
      }
    }
  
    function cache(scope, ds, name, optype, field, counts, index) {
      var cache = ds[name] || (ds[name] = {}),
          sort = sortKey(counts),
          k = fieldKey(field), v, op;
  
      if (k != null) {
        scope = ds.scope;
        k = k + (sort ? '|' + sort : '');
        v = cache[k];
      }
  
      if (!v) {
        var params = counts
          ? {field: keyFieldRef, pulse: ds.countsRef(scope, field, counts)}
          : {field: scope.fieldRef(field), pulse: ref(ds.output)};
        if (sort) params.sort = scope.sortRef(counts);
        op = scope.add(entry(optype, undefined, params));
        if (index) ds.index[field] = op;
        v = ref(op);
        if (k != null) cache[k] = v;
      }
      return v;
    }
  
    prototype$1n.tuplesRef = function() {
      return ref(this.values);
    };
  
    prototype$1n.extentRef = function(scope, field) {
      return cache(scope, this, 'extent', 'extent', field, false);
    };
  
    prototype$1n.domainRef = function(scope, field) {
      return cache(scope, this, 'domain', 'values', field, false);
    };
  
    prototype$1n.valuesRef = function(scope, field, sort) {
      return cache(scope, this, 'vals', 'values', field, sort || true);
    };
  
    prototype$1n.lookupRef = function(scope, field) {
      return cache(scope, this, 'lookup', 'tupleindex', field, false);
    };
  
    prototype$1n.indataRef = function(scope, field) {
      return cache(scope, this, 'indata', 'tupleindex', field, true, true);
    };
  
    function parseFacet(spec, scope, group) {
      var facet = spec.from.facet,
          name = facet.name,
          data = getDataRef(facet, scope),
          subscope, source, values, op;
  
      if (!facet.name) {
        error('Facet must have a name: ' + $(facet));
      }
      if (!facet.data) {
        error('Facet must reference a data set: ' + $(facet));
      }
  
      if (facet.field) {
        op = scope.add(PreFacet$1({
          field: scope.fieldRef(facet.field),
          pulse: data
        }));
      } else if (facet.groupby) {
        op = scope.add(Facet$1({
          key:   scope.keyRef(facet.groupby),
          group: ref(scope.proxy(group.parent)),
          pulse: data
        }));
      } else {
        error('Facet must specify groupby or field: ' + $(facet));
      }
  
      // initialize facet subscope
      subscope = scope.fork();
      source = subscope.add(Collect$1());
      values = subscope.add(Sieve$1({pulse: ref(source)}));
      subscope.addData(name, new DataScope(subscope, source, source, values));
      subscope.addSignal('parent', null);
  
      // parse faceted subflow
      op.params.subflow = {
        $subflow: parseSpec(spec, subscope).toRuntime()
      };
    }
  
    function parseSubflow(spec, scope, input) {
      var op = scope.add(PreFacet$1({pulse: input.pulse})),
          subscope = scope.fork();
  
      subscope.add(Sieve$1());
      subscope.addSignal('parent', null);
  
      // parse group mark subflow
      op.params.subflow = {
        $subflow: parseSpec(spec, subscope).toRuntime()
      };
    }
  
    function parseTrigger(spec, scope, name) {
      var remove = spec.remove,
          insert = spec.insert,
          toggle = spec.toggle,
          modify = spec.modify,
          values = spec.values,
          op = scope.add(operator()),
          update, expr;
  
      update = 'if(' + spec.trigger + ',modify("'
        + name + '",'
        + [insert, remove, toggle, modify, values]
            .map(function(_) { return _ == null ? 'null' : _; })
            .join(',')
        + '),0)';
  
      expr = parseExpression$1(update, scope);
      op.update = expr.$expr;
      op.params = expr.$params;
    }
  
    function parseMark(spec, scope) {
      var role = getRole(spec),
          group = spec.type === GroupMark,
          facet = spec.from && spec.from.facet,
          layout = spec.layout || role === ScopeRole$1 || role === FrameRole$1,
          nested = role === MarkRole || layout || facet,
          overlap = spec.overlap,
          ops, op, input, store, enc, bound, render, sieve, name,
          joinRef, markRef, encodeRef, layoutRef, boundRef;
  
      // resolve input data
      input = parseData(spec.from, group, scope);
  
      // data join to map tuples to visual items
      op = scope.add(DataJoin$1({
        key:   input.key || (spec.key ? fieldRef(spec.key) : undefined),
        pulse: input.pulse,
        clean: !group
      }));
      joinRef = ref(op);
  
      // collect visual items
      op = store = scope.add(Collect$1({pulse: joinRef}));
  
      // connect visual items to scenegraph
      op = scope.add(Mark$1({
        markdef:     definition$1(spec),
        interactive: interactive(spec.interactive, scope),
        clip:        clip$2(spec.clip, scope),
        context:     {$context: true},
        groups:      scope.lookup(),
        parent:      scope.signals.parent ? scope.signalRef('parent') : null,
        index:       scope.markpath(),
        pulse:       ref(op)
      }));
      markRef = ref(op);
  
      // add visual encoders
      op = enc = scope.add(Encode$1(encoders(
        spec.encode, spec.type, role, spec.style, scope,
        {mod: false, pulse: markRef}
      )));
  
      // monitor parent marks to propagate changes
      op.params.parent = scope.encode();
  
      // add post-encoding transforms, if defined
      if (spec.transform) {
        spec.transform.forEach(function(_) {
          const tx = parseTransform(_, scope),
                md = tx.metadata;
          if (md.generates || md.changes) {
            error('Mark transforms should not generate new data.');
          }
          if (!md.nomod) enc.params.mod = true; // update encode mod handling
          tx.params.pulse = ref(op);
          scope.add(op = tx);
        });
      }
  
      // if item sort specified, perform post-encoding
      if (spec.sort) {
        op = scope.add(SortItems$1({
          sort:  scope.compareRef(spec.sort, true), // stable sort
          pulse: ref(op)
        }));
      }
  
      encodeRef = ref(op);
  
      // add view layout operator if needed
      if (facet || layout) {
        layout = scope.add(ViewLayout$1({
          layout:   scope.objectProperty(spec.layout),
          legends:  scope.legends,
          mark:     markRef,
          pulse:    encodeRef
        }));
        layoutRef = ref(layout);
      }
  
      // compute bounding boxes
      bound = scope.add(Bound$1({mark: markRef, pulse: layoutRef || encodeRef}));
      boundRef = ref(bound);
  
      // if group mark, recurse to parse nested content
      if (group) {
        // juggle layout & bounds to ensure they run *after* any faceting transforms
        if (nested) { ops = scope.operators; ops.pop(); if (layout) ops.pop(); }
  
        scope.pushState(encodeRef, layoutRef || boundRef, joinRef);
        facet ? parseFacet(spec, scope, input)          // explicit facet
            : nested ? parseSubflow(spec, scope, input) // standard mark group
            : parseSpec(spec, scope); // guide group, we can avoid nested scopes
        scope.popState();
  
        if (nested) { if (layout) ops.push(layout); ops.push(bound); }
      }
  
      // if requested, add overlap removal transform
      if (overlap) {
        boundRef = parseOverlap(overlap, boundRef, scope);
      }
  
      // render / sieve items
      render = scope.add(Render$1({pulse: boundRef}));
      sieve = scope.add(Sieve$1({pulse: ref(render)}, undefined, scope.parent()));
  
      // if mark is named, make accessible as reactive geometry
      // add trigger updates if defined
      if (spec.name != null) {
        name = spec.name;
        scope.addData(name, new DataScope(scope, store, render, sieve));
        if (spec.on) spec.on.forEach(function(on) {
          if (on.insert || on.remove || on.toggle) {
            error('Marks only support modify triggers.');
          }
          parseTrigger(on, scope, name);
        });
      }
    }
  
    function parseOverlap(overlap, source, scope) {
      var method = overlap.method,
          bound = overlap.bound,
          sep = overlap.separation, tol;
  
      var params = {
        separation: isSignal(sep) ? scope.signalRef(sep.signal) : sep,
        method: isSignal(method) ? scope.signalRef(method.signal) : method,
        pulse:  source
      };
  
      if (overlap.order) {
        params.sort = scope.compareRef({field: overlap.order});
      }
  
      if (bound) {
        tol = bound.tolerance;
        params.boundTolerance = isSignal(tol) ? scope.signalRef(tol.signal) : +tol;
        params.boundScale = scope.scaleRef(bound.scale);
        params.boundOrient = bound.orient;
      }
  
      return ref(scope.add(Overlap$1(params)));
    }
  
    function parseLegend(spec, scope) {
      var config = scope.config.legend,
          encode = spec.encode || {},
          legendEncode = encode.legend || {},
          name = legendEncode.name || undefined,
          interactive = legendEncode.interactive,
          style = legendEncode.style,
          _ = lookup$5(spec, config),
          entryEncode, entryLayout, params, children,
          type, datum, dataRef, entryRef, group;
  
      // resolve 'canonical' scale name
      var scale = LegendScales.reduce(function(a, b) { return a || spec[b]; }, 0);
      if (!scale) error('Missing valid scale for legend.');
  
      // resolve legend type (symbol, gradient, or discrete gradient)
      type = legendType(spec, scope.scaleType(scale));
  
      // single-element data source for legend group
      datum = {
        title:  spec.title != null,
        type:   type,
        vgrad:  type !== 'symbol' &&  _.isVertical()
      };
      dataRef = ref(scope.add(Collect$1(null, [datum])));
  
      // encoding properties for legend group
      legendEncode = extendEncode(
        buildLegendEncode(_, config), legendEncode, Skip$1
      );
  
      // encoding properties for legend entry sub-group
      entryEncode = {enter: {x: {value: 0}, y: {value: 0}}};
  
      // data source for legend values
      entryRef = ref(scope.add(LegendEntries$1(params = {
        type:    type,
        scale:   scope.scaleRef(scale),
        count:   scope.objectProperty(spec.tickCount),
        values:  scope.objectProperty(spec.values),
        minstep: scope.property(spec.tickMinStep),
        formatType: scope.property(spec.formatType),
        formatSpecifier: scope.property(spec.format)
      })));
  
      // continuous gradient legend
      if (type === Gradient$2) {
        children = [
          legendGradient(spec, scale, config, encode.gradient),
          legendGradientLabels(spec, config, encode.labels, entryRef)
        ];
        // adjust default tick count based on the gradient length
        params.count = params.count || scope.signalRef(
          `max(2,2*floor((${deref(_.gradientLength())})/100))`
        );
      }
  
      // discrete gradient legend
      else if (type === Discrete$1) {
        children = [
          legendGradientDiscrete(spec, scale, config, encode.gradient, entryRef),
          legendGradientLabels(spec, config, encode.labels, entryRef)
        ];
      }
  
      // symbol legend
      else {
        // determine legend symbol group layout
        entryLayout = legendSymbolLayout(spec, config);
        children = [
          legendSymbolGroups(spec, config, encode, entryRef, deref(entryLayout.columns))
        ];
        // pass symbol size information to legend entry generator
        params.size = sizeExpression(spec, scope, children[0].marks);
      }
  
      // generate legend marks
      children = [
        guideGroup(LegendEntryRole, null, null, dataRef, interactive,
                   entryEncode, children, entryLayout)
      ];
  
      // include legend title if defined
      if (datum.title) {
        children.push(legendTitle(spec, config, encode.title, dataRef));
      }
  
      // build legend specification
      group = guideGroup(LegendRole$1, style, name, dataRef, interactive, legendEncode, children);
      if (spec.zindex) group.zindex = spec.zindex;
  
      // parse legend specification
      return parseMark(group, scope);
    }
  
    function legendType(spec, scaleType) {
      var type = spec.type || Symbols$2;
  
      if (!spec.type && scaleCount(spec) === 1 && (spec.fill || spec.stroke)) {
        type = isContinuous(scaleType) ? Gradient$2
          : isDiscretizing(scaleType) ? Discrete$1
          : Symbols$2;
      }
  
      return type !== Gradient$2 ? type
        : isDiscretizing(scaleType) ? Discrete$1
        : Gradient$2;
    }
  
    function scaleCount(spec) {
      return LegendScales.reduce(function(count, type) {
        return count + (spec[type] ? 1 : 0);
      }, 0);
    }
  
    function buildLegendEncode(_, config) {
      var encode = {enter: {}, update: {}};
  
      addEncoders(encode, {
        orient:       _('orient'),
        offset:       _('offset'),
        padding:      _('padding'),
        titlePadding: _('titlePadding'),
        cornerRadius: _('cornerRadius'),
        fill:         _('fillColor'),
        stroke:       _('strokeColor'),
        strokeWidth:  config.strokeWidth,
        strokeDash:   config.strokeDash,
        x:            _('legendX'),
        y:            _('legendY'),
      });
  
      return encode;
    }
  
    function sizeExpression(spec, scope, marks) {
      var size = deref(getChannel('size', spec, marks)),
          strokeWidth = deref(getChannel('strokeWidth', spec, marks)),
          fontSize = deref(getFontSize(marks[1].encode, scope, GuideLabelStyle));
  
      return parseExpression$1(
        `max(ceil(sqrt(${size})+${strokeWidth}),${fontSize})`,
        scope
      );
    }
  
    function getChannel(name, spec, marks) {
      return spec[name]
        ? `scale("${spec[name]}",datum)`
        : getEncoding(name, marks[0].encode);
    }
  
    function getFontSize(encode, scope, style) {
      return getEncoding('fontSize', encode) || getStyle('fontSize', scope, style);
    }
  
    const angleExpr = `item.orient==="${Left$1}"?-90:item.orient==="${Right$1}"?90:0`,
          baselineExpr$1 = `item.orient==="${Bottom$1}"?"${Top$1}":"${Bottom$1}"`;
  
    function parseTitle(spec, scope) {
      spec = isString(spec) ? {text: spec} : spec;
  
      var config = scope.config.title,
          encode = extend({}, spec.encode),
          dataRef, title;
  
      // single-element data source for group title
      dataRef = ref(scope.add(Collect$1(null, [{}])));
  
      // build title specification
      encode.name = spec.name;
      encode.interactive = spec.interactive;
      title = buildTitle(spec, config, encode, dataRef);
      if (spec.zindex) title.zindex = spec.zindex;
  
      // parse title specification
      return parseMark(title, scope);
    }
  
    function buildTitle(spec, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config),
          zero = {value: 0},
          title = spec.text,
          encode;
  
      encode = {
        enter: {opacity: zero},
        update: {opacity: {value: 1}},
        exit: {opacity: zero}
      };
  
      addEncoders(encode, {
        text:       title,
        orient:     _('orient'),
        anchor:     _('anchor'),
        align:      {signal: alignExpr},
        angle:      {signal: angleExpr},
        baseline:   {signal: baselineExpr$1},
        dx:         _('dx'),
        dy:         _('dy'),
        fill:       _('color'),
        font:       _('font'),
        fontSize:   _('fontSize'),
        fontStyle:  _('fontStyle'),
        fontWeight: _('fontWeight'),
        frame:      _('frame'),
        limit:      _('limit'),
        offset:     _('offset') || 0
      }, { // update
        align:      _('align'),
        angle:      _('angle'),
        baseline:   _('baseline')
      });
  
      return guideMark(TextMark, TitleRole$1, spec.style || GroupTitleStyle,
                       null, dataRef, encode, userEncode);
    }
  
    function parseData$1(data, scope) {
      var transforms = [];
  
      if (data.transform) {
        data.transform.forEach(function(tx) {
          transforms.push(parseTransform(tx, scope));
        });
      }
  
      if (data.on) {
        data.on.forEach(function(on) {
          parseTrigger(on, scope, data.name);
        });
      }
  
      scope.addDataPipeline(data.name, analyze(data, scope, transforms));
    }
  
    /**
     * Analyze a data pipeline, add needed operators.
     */
    function analyze(data, scope, ops) {
      var output = [],
          source = null,
          modify = false,
          generate = false,
          upstream, i, n, t, m;
  
      if (data.values) {
        // hard-wired input data set
        if (hasSignal(data.values) || hasSignal(data.format)) {
          // if either values or format has signal, use dynamic loader
          output.push(load$1(scope, data));
          output.push(source = collect());
        } else {
          // otherwise, ingest upon dataflow init
          output.push(source = collect({
            $ingest: data.values,
            $format: data.format
          }));
        }
      } else if (data.url) {
        // load data from external source
        if (hasSignal(data.url) || hasSignal(data.format)) {
          // if either url or format has signal, use dynamic loader
          output.push(load$1(scope, data));
          output.push(source = collect());
        } else {
          // otherwise, request load upon dataflow init
          output.push(source = collect({
            $request: data.url,
            $format: data.format
          }));
        }
      } else if (data.source) {
        // derives from one or more other data sets
        source = upstream = array(data.source).map(function(d) {
          return ref(scope.getData(d).output);
        });
        output.push(null); // populate later
      }
  
      // scan data transforms, add collectors as needed
      for (i=0, n=ops.length; i<n; ++i) {
        t = ops[i];
        m = t.metadata;
  
        if (!source && !m.source) {
          output.push(source = collect());
        }
        output.push(t);
  
        if (m.generates) generate = true;
        if (m.modifies && !generate) modify = true;
  
        if (m.source) source = t;
        else if (m.changes) source = null;
      }
  
      if (upstream) {
        n = upstream.length - 1;
        output[0] = Relay$1({
          derive: modify,
          pulse: n ? upstream : upstream[0]
        });
        if (modify || n) {
          // collect derived and multi-pulse tuples
          output.splice(1, 0, collect());
        }
      }
  
      if (!source) output.push(collect());
      output.push(Sieve$1({}));
      return output;
    }
  
    function collect(values) {
      var s = Collect$1({}, values);
      s.metadata = {source: true};
      return s;
    }
  
    function load$1(scope, data) {
      return Load$1({
        url:    data.url ? scope.property(data.url) : undefined,
        values: data.values ? scope.property(data.values) : undefined,
        format: scope.objectProperty(data.format)
      });
    }
  
    function axisConfig(spec, scope) {
      var config = scope.config,
          orient = spec.orient,
          xy = (orient === Top$1 || orient === Bottom$1) ? config.axisX : config.axisY,
          or = config['axis' + orient[0].toUpperCase() + orient.slice(1)],
          band = scope.scaleType(spec.scale) === 'band' && config.axisBand;
  
      return (xy || or || band)
        ? extend({}, config.axis, xy, or, band)
        : config.axis;
    }
  
    function axisDomain(spec, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config),
          orient = spec.orient,
          encode, enter, update, u, u2, v;
  
      encode = {
        enter: enter = {opacity: zero$1},
        update: update = {opacity: one$1},
        exit: {opacity: zero$1}
      };
  
      addEncoders(encode, {
        stroke:           _('domainColor'),
        strokeDash:       _('domainDash'),
        strokeDashOffset: _('domainDashOffset'),
        strokeWidth:      _('domainWidth'),
        strokeOpacity:    _('domainOpacity')
      });
  
      if (orient === Top$1 || orient === Bottom$1) {
        u = 'x';
        v = 'y';
      } else {
        u = 'y';
        v = 'x';
      }
      u2 = u + '2';
  
      enter[v] = zero$1;
      update[u] = enter[u] = position(spec, 0);
      update[u2] = enter[u2] = position(spec, 1);
  
      return guideMark(RuleMark, AxisDomainRole, null, null, dataRef, encode, userEncode);
    }
  
    function position(spec, pos) {
      return {scale: spec.scale, range: pos};
    }
  
    function axisGrid(spec, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config),
          orient = spec.orient,
          vscale = spec.gridScale,
          sign = (orient === Left$1 || orient === Top$1) ? 1 : -1,
          offset = offsetValue$1(spec.offset, sign),
          encode, enter, exit, update, tickPos, u, v, v2, s;
  
      encode = {
        enter: enter = {opacity: zero$1},
        update: update = {opacity: one$1},
        exit: exit = {opacity: zero$1}
      };
  
      addEncoders(encode, {
        stroke:           _('gridColor'),
        strokeDash:       _('gridDash'),
        strokeDashOffset: _('gridDashOffset'),
        strokeOpacity:    _('gridOpacity'),
        strokeWidth:      _('gridWidth')
      });
  
      tickPos = {
        scale:  spec.scale,
        field:  Value,
        band:   _('bandPosition'),
        round:  _('tickRound'),
        extra:  _('tickExtra'),
        offset: _('tickOffset')
      };
  
      if (orient === Top$1 || orient === Bottom$1) {
        u = 'x';
        v = 'y';
        s = 'height';
      } else {
        u = 'y';
        v = 'x';
        s = 'width';
      }
      v2 = v + '2';
  
      update[u] = enter[u] = exit[u] = tickPos;
  
      if (vscale) {
        update[v] = enter[v] = {scale: vscale, range: 0, mult: sign, offset: offset};
        update[v2] = enter[v2] = {scale: vscale, range: 1, mult: sign, offset: offset};
      } else {
        update[v] = enter[v] = {value: 0, offset: offset};
        update[v2] = enter[v2] = {signal: s, mult: sign, offset: offset};
      }
  
      return guideMark(RuleMark, AxisGridRole, null, Value, dataRef, encode, userEncode);
    }
  
    function offsetValue$1(offset, sign)  {
      if (sign === 1) ; else if (!isObject(offset)) {
        offset = sign * (offset || 0);
      } else {
        var entry = offset = extend({}, offset);
  
        while (entry.mult != null) {
          if (!isObject(entry.mult)) {
            entry.mult *= sign;
            return offset;
          } else {
            entry = entry.mult = extend({}, entry.mult);
          }
        }
  
        entry.mult = sign;
      }
  
      return offset;
    }
  
    function axisTicks(spec, config, userEncode, dataRef, size) {
      var _ = lookup$5(spec, config),
          orient = spec.orient,
          sign = (orient === Left$1 || orient === Top$1) ? -1 : 1,
          encode, enter, exit, update, tickSize, tickPos;
  
      encode = {
        enter: enter = {opacity: zero$1},
        update: update = {opacity: one$1},
        exit: exit = {opacity: zero$1}
      };
  
      addEncoders(encode, {
        stroke:           _('tickColor'),
        strokeDash:       _('tickDash'),
        strokeDashOffset: _('tickDashOffset'),
        strokeOpacity:    _('tickOpacity'),
        strokeWidth:      _('tickWidth')
      });
  
      tickSize = encoder(size);
      tickSize.mult = sign;
  
      tickPos = {
        scale:  spec.scale,
        field:  Value,
        band:   _('bandPosition'),
        round:  _('tickRound'),
        extra:  _('tickExtra'),
        offset: _('tickOffset')
      };
  
      if (orient === Top$1 || orient === Bottom$1) {
        update.y = enter.y = zero$1;
        update.y2 = enter.y2 = tickSize;
        update.x = enter.x = exit.x = tickPos;
      } else {
        update.x = enter.x = zero$1;
        update.x2 = enter.x2 = tickSize;
        update.y = enter.y = exit.y = tickPos;
      }
  
      return guideMark(RuleMark, AxisTickRole, null, Value, dataRef, encode, userEncode);
    }
  
    function flushExpr(scale, threshold, a, b, c) {
      return {
        signal: 'flush(range("' + scale + '"), '
          + 'scale("' + scale + '", datum.value), '
          + threshold + ',' + a + ',' + b + ',' + c + ')'
      };
    }
  
    function axisLabels(spec, config, userEncode, dataRef, size) {
      var _ = lookup$5(spec, config),
          orient = spec.orient,
          sign = (orient === Left$1 || orient === Top$1) ? -1 : 1,
          isXAxis = (orient === Top$1 || orient === Bottom$1),
          scale = spec.scale,
          flush = deref(_('labelFlush')),
          flushOffset = deref(_('labelFlushOffset')),
          flushOn = flush === 0 || !!flush,
          labelAlign = _('labelAlign'),
          labelBaseline = _('labelBaseline'),
          encode, enter, tickSize, tickPos, align, baseline, offset,
          bound, overlap, separation;
  
      tickSize = encoder(size);
      tickSize.mult = sign;
      tickSize.offset = encoder(_('labelPadding') || 0);
      tickSize.offset.mult = sign;
  
      tickPos = {
        scale:  scale,
        field:  Value,
        band:   0.5,
        offset: _('tickOffset')
      };
  
      if (isXAxis) {
        align = labelAlign || (flushOn
          ? flushExpr(scale, flush, '"left"', '"right"', '"center"')
          : 'center');
        baseline = labelBaseline || (orient === Top$1 ? 'bottom' : 'top');
        offset = !labelAlign;
      } else {
        align = labelAlign || (orient === Right$1 ? 'left' : 'right');
        baseline = labelBaseline || (flushOn
          ? flushExpr(scale, flush, '"top"', '"bottom"', '"middle"')
          : 'middle');
        offset = !labelBaseline;
      }
  
      offset = offset && flushOn && flushOffset
        ? flushExpr(scale, flush, '-' + flushOffset, flushOffset, 0)
        : null;
  
      encode = {
        enter: enter = {
          opacity: zero$1,
          x: isXAxis ? tickPos : tickSize,
          y: isXAxis ? tickSize : tickPos
        },
        update: {
          opacity: one$1,
          text: {field: Label},
          x: enter.x,
          y: enter.y
        },
        exit: {
          opacity: zero$1,
          x: enter.x,
          y: enter.y
        }
      };
  
      addEncoders(encode, {
        [isXAxis ? 'dx' : 'dy']: offset,
        align:       align,
        baseline:    baseline,
        angle:       _('labelAngle'),
        fill:        _('labelColor'),
        fillOpacity: _('labelOpacity'),
        font:        _('labelFont'),
        fontSize:    _('labelFontSize'),
        fontWeight:  _('labelFontWeight'),
        fontStyle:   _('labelFontStyle'),
        limit:       _('labelLimit')
      });
  
      bound   = _('labelBound');
      overlap = _('labelOverlap');
      separation = _('labelSeparation');
  
      spec = guideMark(TextMark, AxisLabelRole, GuideLabelStyle, Value, dataRef, encode, userEncode);
  
      // if overlap method or bound defined, request label overlap removal
      if (overlap || bound) {
        spec.overlap = {
          separation: separation,
          method: overlap,
          order: 'datum.index',
          bound: bound ? {scale: scale, orient: orient, tolerance: bound} : null
        };
      }
  
      return spec;
    }
  
    function axisTitle(spec, config, userEncode, dataRef) {
      var _ = lookup$5(spec, config),
          orient = spec.orient,
          sign = (orient === Left$1 || orient === Top$1) ? -1 : 1,
          horizontal = (orient === Top$1 || orient === Bottom$1),
          encode, enter, update, titlePos;
  
      encode = {
        enter: enter = {
          opacity: zero$1,
          anchor: encoder(_('titleAnchor')),
          align: {signal: alignExpr}
        },
        update: update = extend({}, enter, {
          opacity: one$1,
          text: encoder(spec.title)
        }),
        exit: {
          opacity: zero$1
        }
      };
  
      titlePos = {
        signal: `lerp(range("${spec.scale}"), ${anchorExpr(0, 1, 0.5)})`
      };
  
      if (horizontal) {
        update.x = titlePos;
        enter.angle = {value: 0};
        enter.baseline = {value: orient === Top$1 ? 'bottom' : 'top'};
      } else {
        update.y = titlePos;
        enter.angle = {value: sign * 90};
        enter.baseline = {value: 'bottom'};
      }
  
      addEncoders(encode, {
        angle:       _('titleAngle'),
        baseline:    _('titleBaseline'),
        fill:        _('titleColor'),
        fillOpacity: _('titleOpacity'),
        font:        _('titleFont'),
        fontSize:    _('titleFontSize'),
        fontStyle:   _('titleFontStyle'),
        fontWeight:  _('titleFontWeight'),
        limit:       _('titleLimit')
      }, { // require update
        align:       _('titleAlign')
      });
  
      !addEncode(encode, 'x', _('titleX'), 'update')
        && !horizontal && !has('x', userEncode)
        && (encode.enter.auto = {value: true});
  
      !addEncode(encode, 'y', _('titleY'), 'update')
        && horizontal && !has('y', userEncode)
        && (encode.enter.auto = {value: true});
  
      return guideMark(TextMark, AxisTitleRole, GuideTitleStyle, null, dataRef, encode, userEncode);
    }
  
    function parseAxis(spec, scope) {
      var config = axisConfig(spec, scope),
          encode = spec.encode || {},
          axisEncode = encode.axis || {},
          name = axisEncode.name || undefined,
          interactive = axisEncode.interactive,
          style = axisEncode.style,
          _ = lookup$5(spec, config),
          datum, dataRef, ticksRef, size, group, children;
  
      // single-element data source for axis group
      datum = {
        orient: spec.orient,
        ticks:  !!_('ticks'),
        labels: !!_('labels'),
        grid:   !!_('grid'),
        domain: !!_('domain'),
        title:  spec.title != null
      };
      dataRef = ref(scope.add(Collect$1({}, [datum])));
  
      // encoding properties for axis group item
      axisEncode = extendEncode({
        update: {
          offset:       encoder(_('offset') || 0),
          position:     encoder(value(spec.position, 0)),
          titlePadding: encoder(_('titlePadding')),
          minExtent:    encoder(_('minExtent')),
          maxExtent:    encoder(_('maxExtent')),
          range:        {signal: `abs(span(range("${spec.scale}")))`}
        }
      }, encode.axis, Skip$1);
  
      // data source for axis ticks
      ticksRef = ref(scope.add(AxisTicks$1({
        scale:   scope.scaleRef(spec.scale),
        extra:   scope.property(_('tickExtra')),
        count:   scope.objectProperty(spec.tickCount),
        values:  scope.objectProperty(spec.values),
        minstep: scope.property(spec.tickMinStep),
        formatType: scope.property(spec.formatType),
        formatSpecifier: scope.property(spec.format)
      })));
  
      // generate axis marks
      children = [];
  
      // include axis gridlines if requested
      if (datum.grid) {
        children.push(axisGrid(spec, config, encode.grid, ticksRef));
      }
  
      // include axis ticks if requested
      if (datum.ticks) {
        size = _('tickSize');
        children.push(axisTicks(spec, config, encode.ticks, ticksRef, size));
      }
  
      // include axis labels if requested
      if (datum.labels) {
        size = datum.ticks ? size : 0;
        children.push(axisLabels(spec, config, encode.labels, ticksRef, size));
      }
  
      // include axis domain path if requested
      if (datum.domain) {
        children.push(axisDomain(spec, config, encode.domain, dataRef));
      }
  
      // include axis title if defined
      if (datum.title) {
        children.push(axisTitle(spec, config, encode.title, dataRef));
      }
  
      // build axis specification
      group = guideGroup(AxisRole$1, style, name, dataRef, interactive, axisEncode, children);
      if (spec.zindex) group.zindex = spec.zindex;
  
      // parse axis specification
      return parseMark(group, scope);
    }
  
    function parseSpec(spec, scope, preprocessed) {
      var signals = array(spec.signals),
          scales = array(spec.scales);
  
      if (!preprocessed) signals.forEach(function(_) {
        parseSignal(_, scope);
      });
  
      array(spec.projections).forEach(function(_) {
        parseProjection(_, scope);
      });
  
      scales.forEach(function(_) {
        initScale(_, scope);
      });
  
      array(spec.data).forEach(function(_) {
        parseData$1(_, scope);
      });
  
      scales.forEach(function(_) {
        parseScale(_, scope);
      });
  
      signals.forEach(function(_) {
        parseSignalUpdates(_, scope);
      });
  
      array(spec.axes).forEach(function(_) {
        parseAxis(_, scope);
      });
  
      array(spec.marks).forEach(function(_) {
        parseMark(_, scope);
      });
  
      array(spec.legends).forEach(function(_) {
        parseLegend(_, scope);
      });
  
      if (spec.title) {
        parseTitle(spec.title, scope);
      }
  
      scope.parseLambdas();
      return scope;
    }
  
    var defined = toSet(['width', 'height', 'padding', 'autosize']);
  
    function parseView(spec, scope) {
      var config = scope.config,
          op, input, encode, parent, root;
  
      scope.background = spec.background || config.background;
      scope.eventConfig = config.events;
      root = ref(scope.root = scope.add(operator()));
      scope.addSignal('width', spec.width || 0);
      scope.addSignal('height', spec.height || 0);
      scope.addSignal('padding', parsePadding(spec.padding, config));
      scope.addSignal('autosize', parseAutosize(spec.autosize, config));
      scope.legends = scope.objectProperty(config.legend && config.legend.layout);
  
      array(spec.signals).forEach(function(_) {
        if (!defined[_.name]) parseSignal(_, scope);
      });
  
      // Store root group item
      input = scope.add(Collect$1());
  
      // Encode root group item
      encode = extendEncode({
        enter: { x: {value: 0}, y: {value: 0} },
        update: { width: {signal: 'width'}, height: {signal: 'height'} }
      }, spec.encode);
  
      encode = scope.add(Encode$1(
        encoders(encode, GroupMark, FrameRole$1, spec.style, scope, {pulse: ref(input)}))
      );
  
      // Perform view layout
      parent = scope.add(ViewLayout$1({
        layout:       scope.objectProperty(spec.layout),
        legends:      scope.legends,
        autosize:     scope.signalRef('autosize'),
        mark:         root,
        pulse:        ref(encode)
      }));
      scope.operators.pop();
  
      // Parse remainder of specification
      scope.pushState(ref(encode), ref(parent), null);
      parseSpec(spec, scope, true);
      scope.operators.push(parent);
  
      // Bound / render / sieve root item
      op = scope.add(Bound$1({mark: root, pulse: ref(parent)}));
      op = scope.add(Render$1({pulse: ref(op)}));
      op = scope.add(Sieve$1({pulse: ref(op)}));
  
      // Track metadata for root item
      scope.addData('root', new DataScope(scope, input, input, op));
  
      return scope;
    }
  
    function Scope$1(config) {
      this.config = config;
  
      this.bindings = [];
      this.field = {};
      this.signals = {};
      this.lambdas = {};
      this.scales = {};
      this.events = {};
      this.data = {};
  
      this.streams = [];
      this.updates = [];
      this.operators = [];
      this.background = null;
      this.eventConfig = null;
  
      this._id = 0;
      this._subid = 0;
      this._nextsub = [0];
  
      this._parent = [];
      this._encode = [];
      this._lookup = [];
      this._markpath = [];
    }
  
    function Subscope(scope) {
      this.config = scope.config;
      this.legends = scope.legends;
  
      this.field = Object.create(scope.field);
      this.signals = Object.create(scope.signals);
      this.lambdas = Object.create(scope.lambdas);
      this.scales = Object.create(scope.scales);
      this.events = Object.create(scope.events);
      this.data = Object.create(scope.data);
  
      this.streams = [];
      this.updates = [];
      this.operators = [];
  
      this._id = 0;
      this._subid = ++scope._nextsub[0];
      this._nextsub = scope._nextsub;
  
      this._parent = scope._parent.slice();
      this._encode = scope._encode.slice();
      this._lookup = scope._lookup.slice();
      this._markpath = scope._markpath;
    }
  
    var prototype$1o = Scope$1.prototype = Subscope.prototype;
  
    // ----
  
    prototype$1o.fork = function() {
      return new Subscope(this);
    };
  
    prototype$1o.isSubscope = function() {
      return this._subid > 0;
    };
  
    prototype$1o.toRuntime = function() {
      this.finish();
      return {
        background:  this.background,
        operators:   this.operators,
        streams:     this.streams,
        updates:     this.updates,
        bindings:    this.bindings,
        eventConfig: this.eventConfig
      };
    };
  
    prototype$1o.id = function() {
      return (this._subid ? this._subid + ':' : 0) + this._id++;
    };
  
    prototype$1o.add = function(op) {
      this.operators.push(op);
      op.id = this.id();
      // if pre-registration references exist, resolve them now
      if (op.refs) {
        op.refs.forEach(function(ref) { ref.$ref = op.id; });
        op.refs = null;
      }
      return op;
    };
  
    prototype$1o.proxy = function(op) {
      var vref = op instanceof Entry ? ref(op) : op;
      return this.add(Proxy$1({value: vref}));
    };
  
    prototype$1o.addStream = function(stream) {
      this.streams.push(stream);
      stream.id = this.id();
      return stream;
    };
  
    prototype$1o.addUpdate = function(update) {
      this.updates.push(update);
      return update;
    };
  
    // Apply metadata
    prototype$1o.finish = function() {
      var name, ds;
  
      // annotate root
      if (this.root) this.root.root = true;
  
      // annotate signals
      for (name in this.signals) {
        this.signals[name].signal = name;
      }
  
      // annotate scales
      for (name in this.scales) {
        this.scales[name].scale = name;
      }
  
      // annotate data sets
      function annotate(op, name, type) {
        var data, list;
        if (op) {
          data = op.data || (op.data = {});
          list = data[name] || (data[name] = []);
          list.push(type);
        }
      }
      for (name in this.data) {
        ds = this.data[name];
        annotate(ds.input,  name, 'input');
        annotate(ds.output, name, 'output');
        annotate(ds.values, name, 'values');
        for (var field in ds.index) {
          annotate(ds.index[field], name, 'index:' + field);
        }
      }
  
      return this;
    };
  
    // ----
  
    prototype$1o.pushState = function(encode, parent, lookup) {
      this._encode.push(ref(this.add(Sieve$1({pulse: encode}))));
      this._parent.push(parent);
      this._lookup.push(lookup ? ref(this.proxy(lookup)) : null);
      this._markpath.push(-1);
    };
  
    prototype$1o.popState = function() {
      this._encode.pop();
      this._parent.pop();
      this._lookup.pop();
      this._markpath.pop();
    };
  
    prototype$1o.parent = function() {
      return peek(this._parent);
    };
  
    prototype$1o.encode = function() {
      return peek(this._encode);
    };
  
    prototype$1o.lookup = function() {
      return peek(this._lookup);
    };
  
    prototype$1o.markpath = function() {
      var p = this._markpath;
      return ++p[p.length-1];
    };
  
    // ----
  
    prototype$1o.fieldRef = function(field, name) {
      if (isString(field)) return fieldRef(field, name);
      if (!field.signal) {
        error('Unsupported field reference: ' + $(field));
      }
  
      var s = field.signal,
          f = this.field[s],
          params;
  
      if (!f) {
        params = {name: this.signalRef(s)};
        if (name) params.as = name;
        this.field[s] = f = ref(this.add(Field$1(params)));
      }
      return f;
    };
  
    prototype$1o.compareRef = function(cmp, stable) {
      function check(_) {
        if (isSignal(_)) {
          signal = true;
          return scope.signalRef(_.signal);
        } else if (isExpr(_)) {
          signal = true;
          return scope.exprRef(_.expr);
        } else {
          return _;
        }
      }
  
      var scope = this,
          signal = false,
          fields = array(cmp.field).map(check),
          orders = array(cmp.order).map(check);
  
      if (stable) {
        fields.push(tupleidRef);
      }
  
      return signal
        ? ref(this.add(Compare$1({fields: fields, orders: orders})))
        : compareRef(fields, orders);
    };
  
    prototype$1o.keyRef = function(fields, flat) {
      function check(_) {
        if (isSignal(_)) {
          signal = true;
          return ref(sig[_.signal]);
        } else {
          return _;
        }
      }
  
      var sig = this.signals,
          signal = false;
      fields = array(fields).map(check);
  
      return signal
        ? ref(this.add(Key$1({fields: fields, flat: flat})))
        : keyRef(fields, flat);
    };
  
    prototype$1o.sortRef = function(sort) {
      if (!sort) return sort;
  
      // including id ensures stable sorting
      var a = [aggrField(sort.op, sort.field), tupleidRef],
          o = sort.order || Ascending;
  
      return o.signal
        ? ref(this.add(Compare$1({
            fields: a,
            orders: [o = this.signalRef(o.signal), o]
          })))
        : compareRef(a, [o, o]);
    };
  
    // ----
  
    prototype$1o.event = function(source, type) {
      var key = source + ':' + type;
      if (!this.events[key]) {
        var id = this.id();
        this.streams.push({
          id: id,
          source: source,
          type: type
        });
        this.events[key] = id;
      }
      return this.events[key];
    };
  
    // ----
  
    prototype$1o.addSignal = function(name, value) {
      if (this.signals.hasOwnProperty(name)) {
        error('Duplicate signal name: ' + $(name));
      }
      var op = value instanceof Entry ? value : this.add(operator(value));
      return this.signals[name] = op;
    };
  
    prototype$1o.getSignal = function(name) {
      if (!this.signals[name]) {
        error('Unrecognized signal name: ' + $(name));
      }
      return this.signals[name];
    };
  
    prototype$1o.signalRef = function(s) {
      if (this.signals[s]) {
        return ref(this.signals[s]);
      } else if (!this.lambdas.hasOwnProperty(s)) {
        this.lambdas[s] = this.add(operator(null));
      }
      return ref(this.lambdas[s]);
    };
  
    prototype$1o.parseLambdas = function() {
      var code = Object.keys(this.lambdas);
      for (var i=0, n=code.length; i<n; ++i) {
        var s = code[i],
            e = parseExpression$1(s, this),
            op = this.lambdas[s];
        op.params = e.$params;
        op.update = e.$expr;
      }
    };
  
    prototype$1o.property = function(spec) {
      return spec && spec.signal ? this.signalRef(spec.signal) : spec;
    };
  
    prototype$1o.objectProperty = function(spec) {
      return (!spec || !isObject(spec)) ? spec
        : this.signalRef(spec.signal || propertyLambda(spec));
    };
  
    function propertyLambda(spec) {
      return (isArray(spec) ? arrayLambda : objectLambda)(spec);
    }
  
    function arrayLambda(array) {
      var code = '[',
          i = 0,
          n = array.length,
          value;
  
      for (; i<n; ++i) {
        value = array[i];
        code += (i > 0 ? ',' : '')
          + (isObject(value)
            ? (value.signal || propertyLambda(value))
            : $(value));
      }
      return code + ']';
    }
  
    function objectLambda(obj) {
      var code = '{',
          i = 0,
          key, value;
  
      for (key in obj) {
        value = obj[key];
        code += (++i > 1 ? ',' : '')
          + $(key) + ':'
          + (isObject(value)
            ? (value.signal || propertyLambda(value))
            : $(value));
      }
      return code + '}';
    }
  
    prototype$1o.exprRef = function(code, name) {
      var params = {expr: parseExpression$1(code, this)};
      if (name) params.expr.$name = name;
      return ref(this.add(Expression$1(params)));
    };
  
    prototype$1o.addBinding = function(name, bind) {
      if (!this.bindings) {
        error('Nested signals do not support binding: ' + $(name));
      }
      this.bindings.push(extend({signal: name}, bind));
    };
  
    // ----
  
    prototype$1o.addScaleProj = function(name, transform) {
      if (this.scales.hasOwnProperty(name)) {
        error('Duplicate scale or projection name: ' + $(name));
      }
      this.scales[name] = this.add(transform);
    };
  
    prototype$1o.addScale = function(name, params) {
      this.addScaleProj(name, Scale$1(params));
    };
  
    prototype$1o.addProjection = function(name, params) {
      this.addScaleProj(name, Projection$1(params));
    };
  
    prototype$1o.getScale = function(name) {
      if (!this.scales[name]) {
        error('Unrecognized scale name: ' + $(name));
      }
      return this.scales[name];
    };
  
    prototype$1o.projectionRef =
    prototype$1o.scaleRef = function(name) {
      return ref(this.getScale(name));
    };
  
    prototype$1o.projectionType =
    prototype$1o.scaleType = function(name) {
      return this.getScale(name).params.type;
    };
  
    // ----
  
    prototype$1o.addData = function(name, dataScope) {
      if (this.data.hasOwnProperty(name)) {
        error('Duplicate data set name: ' + $(name));
      }
      return (this.data[name] = dataScope);
    };
  
    prototype$1o.getData = function(name) {
      if (!this.data[name]) {
        error('Undefined data set name: ' + $(name));
      }
      return this.data[name];
    };
  
    prototype$1o.addDataPipeline = function(name, entries) {
      if (this.data.hasOwnProperty(name)) {
        error('Duplicate data set name: ' + $(name));
      }
      return this.addData(name, DataScope.fromEntries(this, entries));
    };
  
    function defaults(configs) {
      return (configs || []).reduce((out, config) => {
        for (var key in config) {
          var r = key === 'legend' ? {'layout': 1}
            : key === 'style' ? true : null;
          copy$1(out, key, config[key], r);
        }
        return out;
      }, defaults$1());
    }
  
    function copy$1(output, key, value, recurse) {
      var k, o;
      if (isObject(value) && !isArray(value)) {
        o = isObject(output[key]) ? output[key] : (output[key] = {});
        for (k in value) {
          if (recurse && (recurse === true || recurse[k])) {
            copy$1(o, k, value[k]);
          } else {
            o[k] = value[k];
          }
        }
      } else {
        output[key] = value;
      }
    }
  
    var defaultFont = 'sans-serif',
        defaultSymbolSize = 30,
        defaultStrokeWidth = 2,
        defaultColor = '#4c78a8',
        black = '#000',
        gray = '#888',
        lightGray = '#ddd';
  
    /**
     * Standard configuration defaults for Vega specification parsing.
     * Users can provide their own (sub-)set of these default values
     * by passing in a config object to the top-level parse method.
     */
    function defaults$1() {
      return {
        // default padding around visualization
        padding: 0,
  
        // default for automatic sizing; options: 'none', 'pad', 'fit'
        // or provide an object (e.g., {'type': 'pad', 'resize': true})
        autosize: 'pad',
  
        // default view background color
        // covers the entire view component
        background: null,
  
        // default event handling configuration
        // preventDefault for view-sourced event types except 'wheel'
        events: {
          defaults: {allow: ['wheel']}
        },
  
        // defaults for top-level group marks
        // accepts mark properties (fill, stroke, etc)
        // covers the data rectangle within group width/height
        group: null,
  
        // defaults for basic mark types
        // each subset accepts mark properties (fill, stroke, etc)
        mark: null,
        arc: { fill: defaultColor },
        area: { fill: defaultColor },
        image: null,
        line: {
          stroke: defaultColor,
          strokeWidth: defaultStrokeWidth
        },
        path: { stroke: defaultColor },
        rect: { fill: defaultColor },
        rule: { stroke: black },
        shape: { stroke: defaultColor },
        symbol: {
          fill: defaultColor,
          size: 64
        },
        text: {
          fill: black,
          font: defaultFont,
          fontSize: 11
        },
  
        // style definitions
        style: {
          // axis & legend labels
          'guide-label': {
            fill: black,
            font: defaultFont,
            fontSize: 10
          },
          // axis & legend titles
          'guide-title': {
            fill: black,
            font: defaultFont,
            fontSize: 11,
            fontWeight: 'bold'
          },
          // headers, including chart title
          'group-title': {
            fill: black,
            font: defaultFont,
            fontSize: 13,
            fontWeight: 'bold'
          },
          // defaults for styled point marks in Vega-Lite
          point: {
            size: defaultSymbolSize,
            strokeWidth: defaultStrokeWidth,
            shape: 'circle'
          },
          circle: {
            size: defaultSymbolSize,
            strokeWidth: defaultStrokeWidth
          },
          square: {
            size: defaultSymbolSize,
            strokeWidth: defaultStrokeWidth,
            shape: 'square'
          },
          // defaults for styled group marks in Vega-Lite
          cell: {
            fill: 'transparent',
            stroke: lightGray
          }
        },
  
        // defaults for title
        title: {
          orient: 'top',
          anchor: 'middle',
          offset: 4
        },
  
        // defaults for axes
        axis: {
          minExtent: 0,
          maxExtent: 200,
          bandPosition: 0.5,
          domain: true,
          domainWidth: 1,
          domainColor: gray,
          grid: false,
          gridWidth: 1,
          gridColor: lightGray,
          labels: true,
          labelAngle: 0,
          labelLimit: 180,
          labelPadding: 2,
          ticks: true,
          tickColor: gray,
          tickOffset: 0,
          tickRound: true,
          tickSize: 5,
          tickWidth: 1,
          titlePadding: 4
        },
  
        // correction for centering bias
        axisBand: {
          tickOffset: -1
        },
  
        // defaults for legends
        legend: {
          orient: 'right',
          padding: 0,
          gridAlign: 'each',
          columnPadding: 10,
          rowPadding: 2,
          symbolDirection: 'vertical',
          gradientDirection: 'vertical',
          gradientLength: 200,
          gradientThickness: 16,
          gradientStrokeColor: lightGray,
          gradientStrokeWidth: 0,
          gradientLabelOffset: 2,
          labelAlign: 'left',
          labelBaseline: 'middle',
          labelLimit: 160,
          labelOffset: 4,
          labelOverlap: true,
          symbolType: 'circle',
          symbolSize: 100,
          symbolOffset: 0,
          symbolStrokeWidth: 1.5,
          symbolBaseFillColor: 'transparent',
          symbolBaseStrokeColor: gray,
          titleLimit: 180,
          titleOrient: 'top',
          titlePadding: 5,
          layout: {
            offset: 18,
            direction: 'horizontal',
            left:   { direction: 'vertical' },
            right:  { direction: 'vertical' }
          }
        },
  
        // defaults for scale ranges
        range: {
          category: {
            scheme: 'tableau10'
          },
          ordinal: {
            scheme: 'blues'
          },
          heatmap: {
            scheme: 'yellowgreenblue'
          },
          ramp: {
            scheme: 'blues'
          },
          diverging: {
            scheme: 'blueorange',
            extent: [1, 0]
          },
          symbol: [
            'circle',
            'square',
            'triangle-up',
            'cross',
            'diamond',
            'triangle-right',
            'triangle-down',
            'triangle-left'
          ]
        }
      };
    }
  
    function parse$5(spec, config) {
      if (!isObject(spec)) error('Input Vega specification must be an object.');
      return parseView(spec, new Scope$1(defaults([config, spec.config])))
        .toRuntime();
    }
  
    // -- Transforms -----
    extend(transforms, tx, vtx, encode, geo, force, tree, reg, voronoi, wordcloud, xf);
  
    Object.defineProperty(exports, 'timeFormatLocale', {
      enumerable: true,
      get: function () {
        return d3TimeFormat.timeFormatDefaultLocale;
      }
    });
    Object.defineProperty(exports, 'formatLocale', {
      enumerable: true,
      get: function () {
        return d3Format.formatDefaultLocale;
      }
    });
    exports.Bounds = Bounds;
    exports.CanvasHandler = CanvasHandler;
    exports.CanvasRenderer = CanvasRenderer;
    exports.Dataflow = Dataflow;
    exports.Debug = Debug;
    exports.Error = Error$1;
    exports.EventStream = EventStream;
    exports.Gradient = Gradient;
    exports.GroupItem = GroupItem;
    exports.Handler = Handler;
    exports.Info = Info;
    exports.Item = Item;
    exports.Marks = Marks;
    exports.MultiPulse = MultiPulse;
    exports.None = None;
    exports.Operator = Operator;
    exports.Parameters = Parameters;
    exports.Pulse = Pulse;
    exports.RenderType = RenderType;
    exports.Renderer = Renderer;
    exports.ResourceLoader = ResourceLoader;
    exports.SVGHandler = SVGHandler;
    exports.SVGRenderer = SVGRenderer;
    exports.SVGStringRenderer = SVGStringRenderer;
    exports.Scenegraph = Scenegraph;
    exports.Transform = Transform;
    exports.View = View;
    exports.Warn = Warn;
    exports.accessor = accessor;
    exports.accessorFields = accessorFields;
    exports.accessorName = accessorName;
    exports.array = array;
    exports.bin = bin;
    exports.bootstrapCI = bootstrapCI;
    exports.boundClip = boundClip;
    exports.boundContext = context;
    exports.boundItem = boundItem;
    exports.boundMark = boundMark;
    exports.boundStroke = boundStroke;
    exports.changeset = changeset;
    exports.clampRange = clampRange;
    exports.closeTag = closeTag;
    exports.compare = compare;
    exports.constant = constant;
    exports.debounce = debounce;
    exports.definition = definition;
    exports.domChild = domChild;
    exports.domClear = domClear;
    exports.domCreate = domCreate;
    exports.domFind = domFind;
    exports.error = error;
    exports.expressionFunction = expressionFunction;
    exports.extend = extend;
    exports.extent = extent;
    exports.extentIndex = extentIndex;
    exports.falsy = falsy;
    exports.fastmap = fastmap;
    exports.field = field;
    exports.flush = flush;
    exports.font = font;
    exports.fontFamily = fontFamily;
    exports.fontSize = fontSize;
    exports.format = format;
    exports.formats = formats;
    exports.id = id;
    exports.identity = identity;
    exports.inferType = inferType;
    exports.inferTypes = inferTypes;
    exports.ingest = ingest;
    exports.inherits = inherits;
    exports.inrange = inrange;
    exports.interpolate = interpolate;
    exports.interpolateColors = interpolateColors;
    exports.interpolateRange = interpolateRange;
    exports.intersect = intersect;
    exports.intersectBoxLine = intersectBoxLine;
    exports.intersectPath = intersectPath;
    exports.intersectPoint = intersectPoint;
    exports.intersectRule = intersectRule;
    exports.isArray = isArray;
    exports.isBoolean = isBoolean;
    exports.isDate = isDate;
    exports.isFunction = isFunction;
    exports.isNumber = isNumber;
    exports.isObject = isObject;
    exports.isRegExp = isRegExp;
    exports.isString = isString;
    exports.isTuple = isTuple;
    exports.key = key;
    exports.lerp = lerp;
    exports.loader = loader;
    exports.logger = logger;
    exports.merge = merge;
    exports.one = one;
    exports.openTag = openTag;
    exports.pad = pad;
    exports.panLinear = panLinear;
    exports.panLog = panLog;
    exports.panPow = panPow;
    exports.panSymlog = panSymlog;
    exports.parse = parse$5;
    exports.pathCurves = curves;
    exports.pathEqual = pathEqual;
    exports.pathParse = pathParse;
    exports.pathRectangle = vg_rect;
    exports.pathRender = pathRender;
    exports.pathSymbols = symbols;
    exports.pathTrail = vg_trail;
    exports.peek = peek;
    exports.point = point;
    exports.projection = projection;
    exports.quantizeInterpolator = quantizeInterpolator;
    exports.quarter = quarter;
    exports.quartiles = quartiles;
    exports.randomInteger = integer;
    exports.randomKDE = randomKDE;
    exports.randomLCG = lcg;
    exports.randomMixture = randomMixture;
    exports.randomNormal = randomNormal;
    exports.randomUniform = randomUniform;
    exports.read = read;
    exports.regressionExp = regressionExp;
    exports.regressionLinear = regressionLinear;
    exports.regressionLoess = regressionLoess;
    exports.regressionLog = regressionLog;
    exports.regressionPoly = regressionPoly;
    exports.regressionPow = regressionPow;
    exports.regressionQuad = regressionQuad;
    exports.renderModule = renderModule;
    exports.repeat = repeat;
    exports.resetSVGClipId = resetSVGClipId;
    exports.responseType = responseType;
    exports.runtime = parse$4;
    exports.runtimeContext = context$2;
    exports.sampleCurve = sampleCurve;
    exports.scale = scale$1;
    exports.sceneEqual = sceneEqual;
    exports.sceneFromJSON = sceneFromJSON;
    exports.scenePickVisit = pickVisit;
    exports.sceneToJSON = sceneToJSON;
    exports.sceneVisit = visit;
    exports.sceneZOrder = zorder;
    exports.scheme = scheme;
    exports.setRandom = setRandom;
    exports.span = span;
    exports.splitAccessPath = splitAccessPath;
    exports.stringValue = $;
    exports.textMetrics = textMetrics;
    exports.timeInterval = timeInterval;
    exports.toBoolean = toBoolean;
    exports.toDate = toDate;
    exports.toNumber = toNumber;
    exports.toSet = toSet;
    exports.toString = toString;
    exports.transform = transform;
    exports.transforms = transforms;
    exports.truncate = truncate;
    exports.truthy = truthy;
    exports.tupleid = tupleid;
    exports.typeParsers = typeParsers;
    exports.utcquarter = utcquarter;
    exports.version = version;
    exports.visitArray = visitArray;
    exports.zero = zero;
    exports.zoomLinear = zoomLinear;
    exports.zoomLog = zoomLog;
    exports.zoomPow = zoomPow;
    exports.zoomSymlog = zoomSymlog;
  
    Object.defineProperty(exports, '__esModule', { value: true });
  
  }));
  