title: d3.min.js Uncaught TypeError: a.map is not a function
body: <p>I'm starting to use D3 and I'm trying to work with an <a href="http://zeroviscosity.com/d3-js-step-by-step/step-1-a-basic-pie-chart" rel="nofollow">example</a> using my own JSON. The code is showing Uncaught TypeError: a.map is not a function, but the JSON is already parsed, so I don't know what can be.</p>
  
  <p>This is my code:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
    &lt;head&gt;
      &lt;meta charset="utf-8"&gt;
      &lt;title&gt;Step 1 - A Basic Pie Chart&lt;/title&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;div id="chart"&gt;&lt;/div&gt;
      &lt;script type=text/javascript src="{{url_for('static', filename='d3.min.js') }}"&gt;&lt;/script&gt;
      &lt;script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"&gt;&lt;/script&gt;
      &lt;script&gt;
        (function(d3) {
          'use strict';
  
          var width = 360;
          var height = 360;
          var radius = Math.min(width, height) / 2;
  
          var color = d3.scale.category20b();
  
          var svg = d3.select('#chart')
            .append('svg')
            .attr('width', width)
            .attr('height', height)
            .append('g')
            .attr('transform', 'translate(' + (width / 2) + 
              ',' + (height / 2) + ')');
  
          var arc = d3.svg.arc()
            .outerRadius(radius);
  
          var pie = d3.layout.pie()
            .value(function(d) { return d.Value; })
            .sort(null);
  
          d3.json('https://demo-url.com/api/v1.0/tables/56afce8f243c48393e5b665a'
              , function(error, dataset){
                if (error) throw error;
  
            var path = svg.selectAll('path')
              .data(pie(dataset))
              .enter()
              .append('path')
              .attr('d', arc)
              .attr('fill', function(d, i) { 
                return color(d.data.Name);
              });
  
          }); 
  
        })(window.d3);
      &lt;/script&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>This is what the page JSON returns:</p>
  
  <pre><code>curl -i -X GET https://demo-url.com/api/v1.0/tables/56afce8f243c48393e5b665a
  HTTP/1.1 200 OK
  content-type: application/json
  content-length: 702
  server: Werkzeug/0.11.3 Python/2.7.6
  date: Wed, 03 Feb 2016 02:56:32 GMT
  X-BACKEND: apps-proxy
  
  {"data": [{"_id": {"$oid": "56afcea3243c48393e5b665f"}, "idDatasource": {"$oid": "56afce8f243c48393e5b665a"}, "Id": 5, "Value": 0, "Name": "Brock"}, {"_id": {"$oid": "56afcea3243c48393e5b665d"}, "idDatasource": {"$oid": "56afce8f243c48393e5b665a"}, "Id": 3, "Value": 0, "Name": "Peter"}, {"_id": {"$oid": "56afcea3243c48393e5b665e"}, "idDatasource": {"$oid": "56afce8f243c48393e5b665a"}, "Id": 4, "Value": 0, "Name": "John"}, {"_id": {"$oid": "56afcea3243c48393e5b665b"}, "idDatasource": {"$oid": "56afce8f243c48393e5b665a"}, "Id": 1, "Value": 0, "Name": "Ash"}, {"_id": {"$oid": "56afcea3243c48393e5b665c"}, "idDatasource": {"$oid": "56afce8f243c48393e5b665a"}, "Id": 2, "Value": 0, "Name": "Sarah"}]}
  </code></pre>