Pie Chart Update, IV

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

Building on the previous version, this variation of a donut chart demonstrates a nice transition when the pie chart is drawn for the first time.

Previous: Animated transition of entering & exiting slices.

<!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]
};

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

var enterClockwise = {
  startAngle: 0,
  endAngle: 0
};

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 + ")");

// set the start and end angles to 0 so we can transition
// clockwise to the actual values later
var path = svg.selectAll("path")
  .data(pie(dataset.apples))
  .enter().append("path")
    .attr("fill", function(d, i) { return color(i); })
    .attr("d", arc(enterClockwise))
    .each(function(d) {
      this._current = {
        data: d.data,
        value: d.value,
        startAngle: enterClockwise.startAngle,
        endAngle: enterClockwise.endAngle
      }
    }); // store the initial values

path.transition()  // update
    .duration(750)
    .attrTween("d", arcTween);

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));
  };
}
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