Pie Chart Update, III

The easiest way to transition between pie charts with differently-sized datasets (while maintaining object constancy) is to set the missing values to zero.

function type(d) {
  d.apples = +d.apples || 0;
  d.oranges = +d.oranges || 0;
  return d;
}

Next: Static Data-Join
Previous: Animation

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

body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  margin: auto;
  position: relative;
  width: 960px;
}

text {
  font: 10px sans-serif;
}

form {
  position: absolute;
  right: 10px;
  top: 10px;
}

</style>
<form>
  <label><input type="radio" name="dataset" value="apples" checked> Apples</label>
  <label><input type="radio" name="dataset" value="oranges"> Oranges</label>
</form>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

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

var color = d3.scale.category20();

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

var arc = d3.svg.arc()
    .innerRadius(radius - 100)
    .outerRadius(radius - 20);

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

d3.tsv("data.tsv", type, function(error, data) {
  var path = svg.datum(data).selectAll("path")
      .data(pie)
    .enter().append("path")
      .attr("fill", function(d, i) { return color(i); })
      .attr("d", arc)
      .each(function(d) { this._current = d; }); // store the initial angles

d3.selectAll("input")
      .on("change", change);

var timeout = setTimeout(function() {
    d3.select("input[value=\"oranges\"]").property("checked", true).each(change);
  }, 2000);

function change() {
    var value = this.value;
    clearTimeout(timeout);
    pie.value(function(d) { return d[value]; }); // change the value function
    path = path.data(pie); // compute the new angles
    path.transition().duration(750).attrTween("d", arcTween); // redraw the arcs
  }
});

function type(d) {
  d.apples = +d.apples || 0;
  d.oranges = +d.oranges || 0;
  return d;
}

// Store the displayed angles in _current.
// Then, interpolate from _current to the new angles.
// During the transition, _current is updated in-place by d3.interpolate.
function arcTween(a) {
  var i = d3.interpolate(this._current, a);
  this._current = i(0);
  return function(t) {
    return arc(i(t));
  };
}

</script>

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