score:11

Accepted answer

For creating a grouped bar chart, you have to set 2 scales for the x position:

var x = d3.scaleBand().rangeRound([0, width])
  .padding(0.1);

var x1 = d3.scaleBand()
  .rangeRound([0, x.bandwidth()])
  .padding(0.05);

Then, you append groups using the first scale...

var groups = g.selectAll(null)
  .data(data)
  .enter()
  .append("g")
  .attr("transform", function(d) {
    return "translate(" + x(d.months) + ",0)";
  })

... and, inside each group, you append the rects using the second scale.

Here is the demo:

var svg = d3.select("svg"),
  margin = {
    top: 20,
    right: 20,
    bottom: 30,
    left: 40
  },
  width = +svg.attr("width") - margin.left - margin.right,
  height = +svg.attr("height") - margin.top - margin.bottom;

var color = d3.scaleOrdinal(d3.schemeCategory10);

var x = d3.scaleBand().rangeRound([0, width])
  .padding(0.1),
  y = d3.scaleLinear().rangeRound([height, 0]);

var g = svg.append("g")
  .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var data = [{
  "Group": "Mars",
  "count": 10,
  "months": "June"
}, {
  "Group": "Jupiter",
  "count": 50,
  "months": "June"
}, {
  "Group": "Mars",
  "count": 70,
  "months": "July"
}, {
  "Group": "Jupiter",
  "count": 60,
  "months": "July"
}];

var ymaxdomain = d3.max(data, function(d) {
  return d.count;
});
x.domain(data.map(function(d) {
  return d.months
}));
y.domain([0, ymaxdomain]);

var x1 = d3.scaleBand()
  .rangeRound([0, x.bandwidth()])
  .padding(0.05)
  .domain(data.map(function(d) {
    return d.Group;
  }));

color.domain(data.map(function(d) {
  return d.Group;
}));

var groups = g.selectAll(null)
  .data(data)
  .enter()
  .append("g")
  .attr("transform", function(d) {
    return "translate(" + x(d.months) + ",0)";
  })

var bars = groups.selectAll(null)
  .data(function(d) {
    return [d]
  })
  .enter()
  .append("rect")
  .attr("x", function(d, i) {
    return x1(d.Group)
  })
  .attr("y", function(d) {
    return y(d.count);
  })
  .attr("width", x1.bandwidth())
  .attr("height", function(d) {
    return height - y(d.count);
  })
  .attr("fill", function(d) {
    return color(d.Group)
  })

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

g.append("g")
  .attr("class", "axis")
  .call(d3.axisLeft(y).ticks(null, "s"))
  .append("text")
  .attr("x", 2)
  .attr("y", y(y.ticks().pop()) + 0.5)
  .attr("dy", "0.32em")
  .attr("fill", "#000")
  .attr("font-weight", "bold")
  .attr("text-anchor", "start")
  .text("count");
.bar {
  fill: steelblue;
  stroke: black
}
<svg width="600" height="600"></svg>
<script src="//d3js.org/d3.v4.min.js"></script>


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