tomgp · April 30, 2021 07:49
diff --git a/index.html b/index.html
 <script src="https://d3js.org/d3.v6.min.js"></script>
 <style>
  svg{border:1px solid black;}
  *{font-family: sans-serif;}
 </style>
 <body>
 <svg width="500" height="500">
 </svg>
 <p>Example of grouped bars where each group has a different number of members</p>
 <p>A response to this question on Stack Overflow: <a href="">d3js grouped bar chart, is this possible?</a></p>
 </body>
 <script>
  // define the groups:
  // each has a name and some arbitrary number of values
  let groups = [
    { name:'one', values:[1,3,6,2] },
    { name:'two', values:[3,5,7,3,2,5] },
    { name:'three', values:[9,2,5] },
    { name:'four', values:[6] }
  ];
  
  // set up some basic infomation about the chart, height, width and margins
  const width= 500;
  const height=500;
  const margin= {top:10,left:10,bottom:20,right:10};
  const plotHeight = height-(margin.top + margin.bottom);
  const plotWidth = width-(margin.left + margin.right);
  const groupPadding = 1.3; // the gap between each group as a proportion of a single bar 
  
  // we need to know how much horizontal space each group needs
  // this depends on the number of values for that group
  // we also need to know where each group starts int he final chart layout so
  // cumulatively add to their starting point via the currentWidth variable
  // in terms of our 'bar' unit
  let currentWidth = 0;
  groups = groups.map(group=>{
    group.width = group.values.length;
    group.startPosition = currentWidth;
    currentWidth += group.width+groupPadding;
    return group;
  });

  // work out the width needed in terms of bars
  // the padding times the number of gaps + the total number of bars 
  const dataXDomain = [0, (groups.length-1)*groupPadding + d3.sum(groups, d=>d.width)];

  // make a scale for the values, 
  // hard coding it here, but in reality you probably want the domain to relect 
  // the values in the data so that if the data changes so does the scale
  const yScale = d3.scaleLinear()
    .domain([0,10])
    .range([plotHeight, margin.top]);

  // ... and for the bars
  const xScale = d3.scaleLinear()
    .domain(dataXDomain)
    .range([0,plotWidth]);

  // Now we're ready to draw the chart!

  //get the SVG and add a group, offset by our defined margins
  const chart = d3.select('svg')
    .append('g')
      .attr(`transform`,`translate(${margin.left},${margin.top})`)
  
  // for each group in the data add a group on the chart
  const barGroups = chart.selectAll('g.bar-group')
    .data(groups)
    .enter()
    .append('g')
    .classed('bar-group', true)
    .attr('transform', group=>`translate(${xScale(group.startPosition)}, 0)`); // postion each bargroup according to its calculated start position and our x-scale
  
  // for each group...
  barGroups.each(function(group){
    const barGroup = d3.select(this)
    
    // add and position a rectangle for each value
    barGroup.selectAll('rect')
      .data(group.values)
      .enter()
      .append('rect')
        .attr('width',xScale(1))
        .attr('height',value=>yScale(value))
        .attr('x',(value, i)=>xScale(i))
        .attr('y',value=>plotHeight - yScale(value))
        .attr('fill','#FFAAAA')
        .attr('stroke','#FF3333')

    //add some labels for the group
    barGroup.append('line')
      .attr('x1',0)
      .attr('x2',xScale(group.width))
      .attr('y1',plotHeight)
      .attr('y2',plotHeight)
      .attr('stroke-width',2)
      .attr('stroke','black')

    barGroup.append('text')
      .text(group=>group.name)
      .attr('transform',`translate(0,${height-margin.bottom+4})`)
  });

 </script>
	<script src="https://d3js.org/d3.v6.min.js"></script>
	<style>
	svg{border:1px solid black;}
	*{font-family: sans-serif;}
	</style>
	<body>
	<svg width="500" height="500">
	</svg>
	<p>Example of grouped bars where each group has a different number of members</p>
	<p>A response to this question on Stack Overflow: <a href="">d3js grouped bar chart, is this possible?</a></p>
	</body>
	<script>
	// define the groups:
	// each has a name and some arbitrary number of values
	let groups = [
	{ name:'one', values:[1,3,6,2] },
	{ name:'two', values:[3,5,7,3,2,5] },
	{ name:'three', values:[9,2,5] },
	{ name:'four', values:[6] }
	];

	// set up some basic infomation about the chart, height, width and margins
	const width= 500;
	const height=500;
	const margin= {top:10,left:10,bottom:20,right:10};
	const plotHeight = height-(margin.top + margin.bottom);
	const plotWidth = width-(margin.left + margin.right);
	const groupPadding = 1.3; // the gap between each group as a proportion of a single bar

	// we need to know how much horizontal space each group needs
	// this depends on the number of values for that group
	// we also need to know where each group starts int he final chart layout so
	// cumulatively add to their starting point via the currentWidth variable
	// in terms of our 'bar' unit
	let currentWidth = 0;
	groups = groups.map(group=>{
	group.width = group.values.length;
	group.startPosition = currentWidth;
	currentWidth += group.width+groupPadding;
	return group;
	});

	// work out the width needed in terms of bars
	// the padding times the number of gaps + the total number of bars
	const dataXDomain = [0, (groups.length-1)*groupPadding + d3.sum(groups, d=>d.width)];

	// make a scale for the values,
	// hard coding it here, but in reality you probably want the domain to relect
	// the values in the data so that if the data changes so does the scale
	const yScale = d3.scaleLinear()
	.domain([0,10])
	.range([plotHeight, margin.top]);

	// ... and for the bars
	const xScale = d3.scaleLinear()
	.domain(dataXDomain)
	.range([0,plotWidth]);

	// Now we're ready to draw the chart!

	//get the SVG and add a group, offset by our defined margins
	const chart = d3.select('svg')
	.append('g')
	.attr(`transform`,`translate(${margin.left},${margin.top})`)

	// for each group in the data add a group on the chart
	const barGroups = chart.selectAll('g.bar-group')
	.data(groups)
	.enter()
	.append('g')
	.classed('bar-group', true)
	.attr('transform', group=>`translate(${xScale(group.startPosition)}, 0)`); // postion each bargroup according to its calculated start position and our x-scale

	// for each group...
	barGroups.each(function(group){
	const barGroup = d3.select(this)

	// add and position a rectangle for each value
	barGroup.selectAll('rect')
	.data(group.values)
	.enter()
	.append('rect')
	.attr('width',xScale(1))
	.attr('height',value=>yScale(value))
	.attr('x',(value, i)=>xScale(i))
	.attr('y',value=>plotHeight - yScale(value))
	.attr('fill','#FFAAAA')
	.attr('stroke','#FF3333')

	//add some labels for the group
	barGroup.append('line')
	.attr('x1',0)
	.attr('x2',xScale(group.width))
	.attr('y1',plotHeight)
	.attr('y2',plotHeight)
	.attr('stroke-width',2)
	.attr('stroke','black')

	barGroup.append('text')
	.text(group=>group.name)
	.attr('transform',`translate(0,${height-margin.bottom+4})`)
	});

	</script>