chart.js 2.1

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.1.0/Chart.bundle.min.js"></script>
<canvas id="myChart"></canvas>

JavaScript

Chart.defaults.groupableBar = Chart.helpers.clone(Chart.defaults.horizontalBar);

var helpers = Chart.helpers;
Chart.controllers.groupableBar = Chart.controllers.horizontalBar.extend({
  calculateBarY: function (index, datasetIndex) {
    // position the bars based on the stack index
    var stackIndex = this.getMeta().stackIndex;
    return Chart.controllers.horizontalBar.prototype.calculateBarY.apply(this, [index, stackIndex]);
  },

  hideOtherStacks: function (datasetIndex) {
    var meta = this.getMeta();
    var stackIndex = meta.stackIndex;

    this.hiddens = [];
    for (var i = 0; i < datasetIndex; i++) {
      var dsMeta = this.chart.getDatasetMeta(i);
      if (dsMeta.stackIndex !== stackIndex) {
        this.hiddens.push(dsMeta.hidden);
        dsMeta.hidden = true;
      }
    }
  },

  unhideOtherStacks: function (datasetIndex) {
    var meta = this.getMeta();
    var stackIndex = meta.stackIndex;

    for (var i = 0; i < datasetIndex; i++) {
      var dsMeta = this.chart.getDatasetMeta(i);
      if (dsMeta.stackIndex !== stackIndex) {
        dsMeta.hidden = this.hiddens.unshift();
      }
    }
  },

  calculateBarX: function (index, datasetIndex) {
    this.hideOtherStacks(datasetIndex);
    var barY = Chart.controllers.horizontalBar.prototype.calculateBarX.apply(this, [index, datasetIndex]);
    this.unhideOtherStacks(datasetIndex);
    return barY;
  },

  calculateBarBase: function (datasetIndex, index) {
    this.hideOtherStacks(datasetIndex);
    var barBase = Chart.controllers.horizontalBar.prototype.calculateBarBase.apply(this, [datasetIndex, index]);
    this.unhideOtherStacks(datasetIndex);
    return barBase;
  },

  getBarCount: function () {
    var stacks = [];

    // put the stack index in the dataset meta
    Chart.helpers.each(this.chart.data.datasets, function (dataset, datasetIndex) {
      var meta = this.chart.getDatasetMeta(datasetIndex);
      if (meta.horizontalBar && this.chart.isDatasetVisible(datasetIndex)) {
       ...