Stacked-to-Grouped Bars

Switch between stacked and grouped layouts using sequenced transitions! Animations preserve object constancy and allow the user to follow the data across views. Animation design by Heer and Robertson. Inspired by Byron and Wattenberg.

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

form {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  position: absolute;
  left: 10px;
  top: 10px;
}

label {
  display: block;
}

</style>
<form>
  <label><input type="radio" name="mode" value="grouped"> Grouped</label>
  <label><input type="radio" name="mode" value="stacked" checked> Stacked</label>
</form>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var n = 5, // The number of series.
    m = 6; // The number of values per series.

// The xz array has m elements, representing the x-values shared by all series.
// The yz array has n elements, representing the y-values of each of the n series.
// Each yz[i] is an array of m non-negative numbers representing a y-value for xz[i].
// The y01z array has the same structure as yz, but with stacked [y₀, y₁] instead of y.
var xz = d3.range(m),
    yz = [[4,3,12,6,2,0],
          [63,76,88,67,68,31],
          [155,174,162,167,35,8],
          [123,154,163,159,176,40],
          [25,29,28,26,31,8]],
    y01z = d3.stack().keys(d3.range(n))(d3.transpose(yz)),
    yMax = d3.max(yz, function(y) { return d3.max(y); }),
    y1Max = d3.max(y01z, function(y) { return d3.max(y, function(d) { return d[1]; }); });

var svg = d3.select("svg"),
    margin = {top: 40, right: 10, bottom: 20, left: 10},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom,
    g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var x = d3.scaleBand()
    .domain(xz)
    .rangeRound([0, width])
    .padding(0.08);

var y = d3.scaleLinear()
    .domain([0, y1Max])
    .range([height, 0]);

var color = d3.scaleOrdinal()
    .domain(d3.range(n))
    .range(d3.schemeCategory20c);

var series = g.selectAll(".series")
  .data(y01z)
  .enter().append("g")
    .attr("fill", function(d, i) { return color(i); });

var rect = series.selectAll("rect")
  .data(function(d) { return d; })
  .enter().append("rect")
    .attr("x", function(d, i) { return x(i); })
    .attr("y", height)
    .attr("width", x.bandwidth())
    .attr("height", 0);

rect.transition()
    .delay(function(d, i) { return i * 10; })
    .attr("y", function(d) { return y(d[1]); })
    .attr("height", function(d) { return y(d[0]) - y(d[1]); });

g.append("g")
    .attr("class", "axis axis--x")
    .attr("transform", "translate(0," + height + ")")
    .call(d3.axisBottom(x)
        .tickSize(0)
        .tickPadding(6));

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

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

function changed() {
  timeout.stop();
  if (this.value === "grouped") transitionGrouped();
  else transitionStacked();
}

function transitionGrouped() {
  y.domain([0, yMax]);

rect.transition()
      .duration(500)
      .delay(function(d, i) { return i * 10; })
      .attr("x", function(d, i) { return x(i) + x.bandwidth() / n * this.parentNode.__data__.key; })
      .attr("width", x.bandwidth() / n)
    .transition()
      .attr("y", function(d) { return y(d[1] - d[0]); })
      .attr("height", function(d) { return y(0) - y(d[1] - d[0]); });
}

function transitionStacked() {
  y.domain([0, y1Max]);

rect.transition()
      .duration(500)
      .delay(function(d, i) { return i * 10; })
      .attr("y", function(d) { return y(d[1]); })
      .attr("height", function(d) { return y(d[0]) - y(d[1]); })
    .transition()
      .attr("x", function(d, i) { return x(i); })
      .attr("width", x.bandwidth());
}

// Returns an array of m psuedorandom, smoothly-varying non-negative numbers.
// Inspired by Lee Byron’s test data generator.
// https://leebyron.com/streamgraph/
function bumps(m) {
  var values = [], i, j, w, x, y, z;

// Initialize with uniform random values in [0.1, 0.2).
  for (i = 0; i < m; ++i) {
    values[i] = 0.1 + 0.1 * Math.random();
  }

// Add five random bumps.
  for (j = 0; j < 5; ++j) {
    x = 1 / (0.1 + Math.random());
    y = 2 * Math.random() - 0.5;
    z = 10 / (0.1 + Math.random());
    for (i = 0; i < m; i++) {
      w = (i / m - y) * z;
      values[i] += x * Math.exp(-w * w);
    }
  }

// Ensure all values are positive.
  for (i = 0; i < m; ++i) {
    values[i] = Math.max(0, values[i]);
  }

return values;
}

</script>

https://d3js.org/d3.v4.min.js