Easy Custom Pie Labels In D3

Easilly create labels for any pie graph using simple trigonometric functions.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  font: 10px sans-serif;
}

.arc path {
  stroke: #fff;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
    height = 500,
    radius = Math.min(width, height) / 2;

var color = d3.scale.ordinal()
    .range(["#98abc5", "#8a89a6", "#7b6888", "#6b486b", "#a05d56", "#d0743c", "#ff8c00"]);

var arc = d3.svg.arc()
    .outerRadius(radius - 30)
    .innerRadius(radius - 100);

var pie = d3.layout.pie()
    .sort(null)
    .value(function(d) { return d.population; });

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

d3.csv("data.csv", function(error, data) {

data.forEach(function(d) {
    d.population = +d.population;
  });

var g = svg.selectAll(".arc")
      .data(pie(data))
    .enter().append("g")
      .attr("class", "arc");

g.append("path")
      .attr("d", arc)
      .style("fill", function(d) { return color(d.data.age); });

g.append("text")
      .attr("transform", function(d) { 
        return "translate(" + ( (radius - 12) * Math.sin( ((d.endAngle - d.startAngle) / 2) + d.startAngle ) ) + "," + ( -1 * (radius - 12) * Math.cos( ((d.endAngle - d.startAngle) / 2) + d.startAngle ) ) + ")"; })
      .attr("dy", ".35em")
      .style("text-anchor", function(d) {
        var rads = ((d.endAngle - d.startAngle) / 2) + d.startAngle;
        if ( (rads > 7 * Math.PI / 4 && rads < Math.PI / 4) || (rads > 3 * Math.PI / 4 && rads < 5 * Math.PI / 4) ) {
          return "middle";
        } else if (rads >= Math.PI / 4 && rads <= 3 * Math.PI / 4) {
          return "start";
        } else if (rads >= 5 * Math.PI / 4 && rads <= 7 * Math.PI / 4) {
          return "end";
        } else {
          return "middle";
        }
      })
      .text(function(d) { 
        return d.data.age; });

});

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js