Circular barplot in d3.js





This post describes how to build a very basic circular barplot with d3.js. You can see many other examples in the circular barplot section of the gallery. Learn more about this type of chart in data-to-viz.com.


Circular barplot section

Steps:

  • The X scale is defined using a scaleBand as for a normal barplot. However then range usually goes between 0 and 2Pi for a complete circle.

  • The Y scale takes advantage of the scaleRadial() function. A scaleLinear() would work as well, but would visually inflate the imprtance of high values as explained here and here.

  • Bars are then added using a path and not a rect. The d3.arc() is a life saver here, learn more about how it works here.

  • This chart is still useless: let's add labels.
<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v4.js"></script>

<!-- Function for radial charts -->
<script src="https://cdn.jsdelivr.net/gh/holtzy/D3-graph-gallery@master/LIB/d3-scale-radial.js"></script>

<!-- Create a div where the graph will take place -->
<div id="my_dataviz"></div>

<script>

// set the dimensions and margins of the graph
var margin = {top: 10, right: 10, bottom: 10, left: 10},
    width = 460 - margin.left - margin.right,
    height = 460 - margin.top - margin.bottom,
    innerRadius = 80,
    outerRadius = Math.min(width, height) / 2;   // the outerRadius goes from the middle of the SVG area to the border

// append the svg object to the body of the page
var svg = d3.select("#my_dataviz")
  .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + width / 2 + "," + ( height/2+100 )+ ")"); // Add 100 on Y translation, cause upper bars are longer

d3.csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/7_OneCatOneNum.csv", function(data) {

  // X scale
  var x = d3.scaleBand()
      .range([0, 2 * Math.PI])    // X axis goes from 0 to 2pi = all around the circle. If I stop at 1Pi, it will be around a half circle
      .align(0)                  // This does nothing ?
      .domain( data.map(function(d) { return d.Country; }) ); // The domain of the X axis is the list of states.

  // Y scale
  var y = d3.scaleRadial()
      .range([innerRadius, outerRadius])   // Domain will be define later.
      .domain([0, 10000]); // Domain of Y is from 0 to the max seen in the data

  // Add bars
  svg.append("g")
    .selectAll("path")
    .data(data)
    .enter()
    .append("path")
      .attr("fill", "#69b3a2")
      .attr("d", d3.arc()     // imagine your doing a part of a donut plot
          .innerRadius(innerRadius)
          .outerRadius(function(d) { return y(d['Value']); })
          .startAngle(function(d) { return x(d.Country); })
          .endAngle(function(d) { return x(d.Country) + x.bandwidth(); })
          .padAngle(0.01)
          .padRadius(innerRadius))

});

</script>

Related blocks →