Grouped Bar Chart

See this more recent, improved version.

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

.axis text {
  font: 10px sans-serif;
}

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

.x.axis path {
  display: none;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var n = 20, // number of samples
    m = 4; // number of series

var data = d3.range(m).map(function() { return d3.range(n).map(Math.random); });

var margin = {top: 20, right: 30, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var y = d3.scale.linear()
    .domain([0, 1])
    .range([height, 0]);

var x0 = d3.scale.ordinal()
    .domain(d3.range(n))
    .rangeBands([0, width], .2);

var x1 = d3.scale.ordinal()
    .domain(d3.range(m))
    .rangeBands([0, x0.rangeBand()]);

var z = d3.scale.category10();

var xAxis = d3.svg.axis()
    .scale(x0)
    .orient("bottom");

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left");

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

svg.append("g")
    .attr("class", "y axis")
    .call(yAxis);

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

svg.append("g").selectAll("g")
    .data(data)
  .enter().append("g")
    .style("fill", function(d, i) { return z(i); })
    .attr("transform", function(d, i) { return "translate(" + x1(i) + ",0)"; })
  .selectAll("rect")
    .data(function(d) { return d; })
  .enter().append("rect")
    .attr("width", x1.rangeBand())
    .attr("height", y)
    .attr("x", function(d, i) { return x0(i); })
    .attr("y", function(d) { return height - y(d); });

</script>

https://d3js.org/d3.v3.min.js