TEST

<!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;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

form {
  position: absolute;
  right: 10px;
  top: 10px;
}

</style>
<form>
  <label><input type="radio" name="mode" value="grouped"> Grouped</label>
  <label><input type="radio" name="mode" value="stacked" checked> Stacked</label>
</form>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
<script>

d3.csv("police_killings.csv", function(err, data) {
  var allRaces = ["Black","Hispanic/Latino",  "White", "Unknown", "Asian/Pacific Islander", "Native American"];
  var months = ["January", "February", "March", "April", "May", "June"]
  console.log("original data", data)
  // we want to "pivot" our data into deaths by month by race
  // this is a rather ugly way to do it in javascript. would probably be easier
  // to group the data in another tool (excel, google sheets, etc) and load that
  var groups = {}
  var races = {};
  var gkey = "raceethnicity" // what we group by
  var xkey = "month" // the x axis
  // first we group all the events by race
  data.forEach(function(d) {
    if(!groups[d[gkey]]) {
      groups[d[gkey]] = [d];
    } else {
      groups[d[gkey]].push(d)
    }
  })
  var processed = [];
  // we are making a "layer" for each race
  allRaces.forEach(function(race,i) {
    var xdata = {};
    groups[race].forEach(function(event) {
      if(!xdata[event[xkey]]) {
        xdata[event[xkey]] = 1
      } else {
        xdata[event[xkey]]++;
      }
    })
    // our "result" is an orered array with a count for each month
    // (for the race we are currently working on)
    var result = [];
    months.forEach(function(g, j) {
      result.push({ x: g, y: xdata[g] || 0 })
    })
    processed.push(result)
  })
  console.log("layer data", processed)

var n = allRaces.length, // number of layers
      m = processed.length, // number of samples per layer
      stack = d3.layout.stack();

var layers = stack(processed); // calculate the stack layout

var margin = {top: 40, right: 10, bottom: 20, left: 10},
      width = 960 - margin.left - margin.right,
      height = 500 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
      .domain(months)
      .rangeRoundBands([0, width], .08);

var y = d3.scale.linear()
      .domain([0, yStackMax])
      .range([height, 0]);

var color = d3.scale.category20c()
      .domain([0, n-1])

var xAxis = d3.svg.axis()
      .scale(x)
      .tickSize(0)
      .tickPadding(6)
      .orient("bottom");

var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var layer = svg.selectAll(".layer")
      .data(layers)
    .enter().append("g")
      .attr("class", "layer")
      .style("fill", function(d, i) { return color(i); });

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

rect.transition()
      .delay(function(d, i) { return i * 10; })
      .attr("y", function(d) { return y(d.y0 + d.y); })
      .attr("height", function(d) { return y(d.y0) - y(d.y0 + d.y); });

svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

var legend = svg.selectAll(".legend")
      .data(allRaces)
    .enter().append("g")
      .attr("class", "legend")
      .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });

legend.append("rect")
      .attr("x", width - 18)
      .attr("width", 18)
      .attr("height", 18)
      .style("fill", function(d,i) { return color(i) });

legend.append("text")
      .attr("x", width - 24)
      .attr("y", 9)
      .attr("dy", ".35em")
      .style("text-anchor", "end")
      .text(function(d) { return d; });

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

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

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

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

rect.transition()
        .duration(500)
        .delay(function(d, i) { return i * 10; })
        .attr("x", function(d, i, j) { return x(d.x) + x.rangeBand() / n * j; })
        .attr("width", x.rangeBand() / n)
      .transition()
        .attr("y", function(d) { return y(d.y); })
        .attr("height", function(d) { return height - y(d.y); });
  }

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

rect.transition()
        .duration(500)
        .delay(function(d, i) { return i * 10; })
        .attr("y", function(d) { return y(d.y0 + d.y); })
        .attr("height", function(d) { return y(d.y0) - y(d.y0 + d.y); })
      .transition()
        .attr("x", function(d) { return x(d.x); })
        .attr("width", x.rangeBand());
  }
});
</script>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js