Pie Chart Update, III

I'm continuting mbostocks's series of gists about pie charts.

This variation of a donut chart demonstrates how to add/remove slices or move between datasets of differing lengths with transitions. Clicking the radio buttons changes the displayed metric. Note how the new slice enters anticlockwise from the 'end' of the pie chart.

Previous: Animated transition. Next: Nice initial transition.

<!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="https://d3js.org/d3.v3.min.js"></script>
<script>

var dataset = {
  apples: [53245, 28479, 19697, 24037, 40245],
  oranges: [200, 200, 200, 200] // previously 5 values, now only 4
};

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

var enterAntiClockwise = {
  startAngle: Math.PI * 2,
  endAngle: Math.PI * 2
};

var color = d3.scale.category20();

var pie = d3.layout.pie()
  .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 + ")");

var path = svg.selectAll("path")
  .data(pie(dataset.apples))
  .enter().append("path")
  .attr("fill", function(d, i) { return color(i); })
  .attr("d", arc)
  .each(function(d) { this._current = d; }); // store the initial values

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

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

path.exit()
      .transition()
      .duration(750)
      .attrTween('d', arcTweenOut)
      .remove() // now remove the exiting arcs

path.transition().duration(750).attrTween("d", arcTween); // redraw the arcs
}

// 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));
  };
}
// Interpolate exiting arcs start and end angles to Math.PI * 2
// so that they 'exit' at the end of the data
function arcTweenOut(a) {
  var i = d3.interpolate(this._current, {startAngle: Math.PI * 2, endAngle: Math.PI * 2, value: 0});
  this._current = i(0);
  return function (t) {
    return arc(i(t));
  };
}

</script>

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

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