Streamgraph

For continuous data such as time series, a streamgraph can be used in place of stacked bars. This example also demonstrates path transitions to interpolate between different layouts. Streamgraph algorithm, colors, and data generation inspired by Byron and Wattenberg.

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

button {
  position: absolute;
  left: 10px;
  top: 10px;
}

</style>
<button onclick="transition()">Update</button>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var n = 20, // number of layers
    m = 200, // number of samples per layer
    k = 10; // number of bumps per layer

var stack = d3.stack().keys(d3.range(n)).offset(d3.stackOffsetWiggle),
    layers0 = stack(d3.transpose(d3.range(n).map(function() { return bumps(m, k); }))),
    layers1 = stack(d3.transpose(d3.range(n).map(function() { return bumps(m, k); }))),
    layers = layers0.concat(layers1);

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height");

var x = d3.scaleLinear()
    .domain([0, m - 1])
    .range([0, width]);

var y = d3.scaleLinear()
    .domain([d3.min(layers, stackMin), d3.max(layers, stackMax)])
    .range([height, 0]);

var z = d3.interpolateCool;

var area = d3.area()
    .x(function(d, i) { return x(i); })
    .y0(function(d) { return y(d[0]); })
    .y1(function(d) { return y(d[1]); });

svg.selectAll("path")
  .data(layers0)
  .enter().append("path")
    .attr("d", area)
    .attr("fill", function() { return z(Math.random()); });

function stackMax(layer) {
  return d3.max(layer, function(d) { return d[1]; });
}

function stackMin(layer) {
  return d3.min(layer, function(d) { return d[0]; });
}

function transition() {
  var t;
  d3.selectAll("path")
    .data((t = layers1, layers1 = layers0, layers0 = t))
    .transition()
      .duration(2500)
      .attr("d", area);
}

// Inspired by Lee Byron’s test data generator.
function bumps(n, m) {
  var a = [], i;
  for (i = 0; i < n; ++i) a[i] = 0;
  for (i = 0; i < m; ++i) bump(a, n);
  return a;
}

function bump(a, n) {
  var x = 1 / (0.1 + Math.random()),
      y = 2 * Math.random() - 0.5,
      z = 10 / (0.1 + Math.random());
  for (var i = 0; i < n; i++) {
    var w = (i / n - y) * z;
    a[i] += x * Math.exp(-w * w);
  }
}

</script>

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