title: Add labels to D3 Chord diagram
body: <p>I'm a rookie programmer, so this one will probably be an easy one for most of you. What lines of code do I need for labels and/or mouse-over text for this Chord diagram?</p>
  
  <p><a href="http://mbostock.github.com/d3/ex/chord.html" rel="noreferrer">http://mbostock.github.com/d3/ex/chord.html</a></p>
  
  <p><img src="https://i.stack.imgur.com/NXI3Y.jpg" alt="enter image description here"></p>
  
  <p>I need it to display the name of the category in the outer strip. When you mouse over, I want to display the exact number and both categories. Something like this: 'A: 5 thing from B'.</p>
  
  <p>EDIT:</p>
  
  <p>I still can't figure out how to implement it in my code. Can someone fill in my example code an explain what's going on?</p>
  
  <pre><code>    &lt;!DOCTYPE html&gt;
  &lt;html&gt;
    &lt;head&gt;
      &lt;meta http-equiv="Content-type" content="text/html; charset=utf-8"&gt;
      &lt;title&gt;Selecties EK 2010&lt;/title&gt;
      &lt;script type="text/javascript" src="d3.v2.js"&gt;&lt;/script&gt;
      &lt;link type="text/css" rel="stylesheet" href="ek2010.css"/&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;div id="chart"&gt;&lt;/div&gt;
      &lt;script type="text/javascript" src="ek2010.js"&gt;&lt;/script&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>and</p>
  
  <pre><code>// From http://mkweb.bcgsc.ca/circos/guide/tables/
  var chord = d3.layout.chord()
      .padding(.05)
      .sortSubgroups(d3.descending)
      .matrix([
        [0, 0, 7, 5],
        [0, 0, 8, 3],
        [7, 8, 0, 0],
        [5, 3, 0, 0]
      ]);
  
  var width = 1000,
      height = 1000,
      innerRadius = Math.min(width, height) * .3,
      outerRadius = innerRadius * 1.1;
  
  var fill = d3.scale.ordinal()
      .domain(d3.range(4))
      .range(["#000000", "#FFDD89", "#957244", "#F26223"]);
  
  var svg = d3.select("#chart")
    .append("svg")
      .attr("width", width)
      .attr("height", height)
    .append("g")
      .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");
  
  svg.append("g")
    .selectAll("path")
      .data(chord.groups)
    .enter().append("path")
      .style("fill", function(d) { return fill(d.index); })
      .style("stroke", function(d) { return fill(d.index); })
      .attr("d", d3.svg.arc().innerRadius(innerRadius).outerRadius(outerRadius))
      .on("mouseover", fade(.1))
      .on("mouseout", fade(1));
  
  var ticks = svg.append("g")
    .selectAll("g")
      .data(chord.groups)
    .enter().append("g")
    .selectAll("g")
      .data(groupTicks)
    .enter().append("g")
      .attr("transform", function(d) {
        return "rotate(" + (d.angle * 180 / Math.PI - 90) + ")"
            + "translate(" + outerRadius + ",0)";
      });
  
  ticks.append("line")
      .attr("x1", 1)
      .attr("y1", 0)
      .attr("x2", 5)
      .attr("y2", 0)
      .style("stroke", "#000");
  
  ticks.append("text")
      .attr("x", 8)
      .attr("dy", ".35em")
      .attr("text-anchor", function(d) {
        return d.angle &gt; Math.PI ? "end" : null;
      })
      .attr("transform", function(d) {
        return d.angle &gt; Math.PI ? "rotate(180)translate(-16)" : null;
      })
      .text(function(d) { return d.label; });
  
  svg.append("g")
      .attr("class", "chord")
    .selectAll("path")
      .data(chord.chords)
    .enter().append("path")
      .style("fill", function(d) { return fill(d.target.index); })
      .attr("d", d3.svg.chord().radius(innerRadius))
      .style("opacity", 1);
  
  /** Returns an array of tick angles and labels, given a group. */
  function groupTicks(d) {
    var k = (d.endAngle - d.startAngle) / d.value;
    return d3.range(0, d.value, 1).map(function(v, i) {
      return {
        angle: v * k + d.startAngle,
        label: i % 5 ? null : v / 1 + " internat."
      };
    });
  }
  
  /** Returns an event handler for fading a given chord group. */
  function fade(opacity) {
    return function(g, i) {
      svg.selectAll("g.chord path")
          .filter(function(d) {
            return d.source.index != i &amp;&amp; d.target.index != i;
          })
        .transition()
          .style("opacity", opacity);
    };
  }
  </code></pre>