D3 Examples - Pie charts labels

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  width: 960px;
  height: 500px;
  position: relative;
}
​
svg {
    width: 100%;
    height: 100%;
}
​
path.slice{
    stroke-width:2px;
}
​
polyline{
    opacity: .3;
    stroke: black;
    stroke-width: 2px;
    fill: none;
}
​
</style>
<body>
<button class="randomize">randomize</button>
​
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
​
var svg = d3.select("body")
    .append("svg")
    .append("g")
​
svg.append("g")
    .attr("class", "slices");
svg.append("g")
    .attr("class", "labels");
svg.append("g")
    .attr("class", "lines");
​
var width = 960,
    height = 450,
    radius = Math.min(width, height) / 2;
​
var pie = d3.layout.pie()
    .sort(null)
    .value(function(d) {
        return d.value;
    });
​
var arc = d3.svg.arc()
    .outerRadius(radius * 0.8)
    .innerRadius(radius * 0.4);
​
var outerArc = d3.svg.arc()
    .innerRadius(radius * 0.9)
    .outerRadius(radius * 0.9);
​
svg.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");
​
var key = function(d){ return d.data.label; };
​
var color = d3.scale.ordinal()
    .domain(["Lorem ipsum", "dolor sit", "amet", "consectetur", "adipisicing", "elit", "sed", "do", "eiusmod", "tempor", "incididunt"])
    .range(["#98abc5", "#8a89a6", "#7b6888", "#6b486b", "#a05d56", "#d0743c", "#ff8c00"]);
​
function randomData (){
    var labels = color.domain();
    return labels.map(function(label){
        return { label: label, value: Math.random() }
    });
}
​
change(randomData());
​
d3.select(".randomize")
    .on("click", function(){
        change(randomData());
    });
​
​
function change(data) {
​
    /* ------- PIE SLICES -------*/
    var slice = svg.select(".slices").selectAll("path.slice")
        .data(pie(data), key);
​
    slice.enter()
        .insert("path")
        .style("fill", function(d) { return color(d.data.label); })
        .attr("class", "slice");
​
    slice       
        .transition().duration(1000)
        .attrTween("d", function(d) {
            this._current = this._current || d;
            var interpolate = d3.interpolate(this._current, d);
            this._current = interpolate(0);
            return function(t) {
                return arc(interpolate(t));
            };
        })
​
    slice.exit()
        .remove();
​
    /* ------- TEXT LABELS -------*/
​
    var text = svg.select(".labels").selectAll("text")
        .data(pie(data), key);
​
    text.enter()
        .append("text")
        .attr("dy", ".35em")
        .text(function(d) {
            return d.data.label;
        });
    
    function midAngle(d){
        return d.startAngle + (d.endAngle - d.startAngle)/2;
    }
​
    text.transition().duration(1000)
        .attrTween("transform", function(d) {
            this._current = this._current || d;
            var interpolate = d3.interpolate(this._current, d);
            this._current = interpolate(0);
            return function(t) {
                var d2 = interpolate(t);
                var pos = outerArc.centroid(d2);
                pos[0] = radius * (midAngle(d2) < Math.PI ? 1 : -1);
                return "translate("+ pos +")";
            };
        })
        .styleTween("text-anchor", function(d){
            this._current = this._current || d;
            var interpolate = d3.interpolate(this._current, d);
            this._current = interpolate(0);
            return function(t) {
                var d2 = interpolate(t);
                return midAngle(d2) < Math.PI ? "start":"end";
            };
        });
​
    text.exit()
        .remove();
​
    /* ------- SLICE TO TEXT POLYLINES -------*/
​
    var polyline = svg.select(".lines").selectAll("polyline")
        .data(pie(data), key);
    
    polyline.enter()
        .append("polyline");
​
    polyline.transition().duration(1000)
        .attrTween("points", function(d){
            this._current = this._current || d;
            var interpolate = d3.interpolate(this._current, d);
            this._current = interpolate(0);
            return function(t) {
                var d2 = interpolate(t);
                var pos = outerArc.centroid(d2);
                pos[0] = radius * 0.95 * (midAngle(d2) < Math.PI ? 1 : -1);
                return [arc.centroid(d2), outerArc.centroid(d2), pos];
            };          
        });
    
    polyline.exit()
        .remove();
};
​
</script>
</body>
    