Most basic correlogram in d3.js





This post describes how to build the most basic correlogram with d3.js. You can see many other examples in the correlogram section of the gallery. Learn more about the theory of correlogram in data-to-viz.com.


Correlogram section

Steps:

  • Disclaimer: This chart is highly inspired from this example.

  • The idea is to create a g element for each cell of the correlogram and store it in an object called cor

  • It is then possible to use .filter to add text to the lower left part of the matrix.

  • And then the upperpart using .circle
<!DOCTYPE html>
<meta charset="utf-8">

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

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

<script>

// Graph dimension
var margin = {top: 20, right: 20, bottom: 20, left: 20},
    width = 430 - margin.left - margin.right,
    height = 430 - margin.top - margin.bottom

// Create the svg area
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(" + margin.left + "," + margin.top + ")");


d3.csv("https://raw.githubusercontent.com/holtzy/D3-graph-gallery/master/DATA/data_correlogram.csv", function(error, rows) {

  // Going from wide to long format
  var data = [];
  rows.forEach(function(d) {
    var x = d[""];
    delete d[""];
    for (prop in d) {
      var y = prop,
        value = d[prop];
      data.push({
        x: x,
        y: y,
        value: +value
      });
    }
  });

  // List of all variables and number of them
  var domain = d3.set(data.map(function(d) { return d.x })).values()
  var num = Math.sqrt(data.length)

  // Create a color scale
  var color = d3.scaleLinear()
    .domain([-1, 0, 1])
    .range(["#B22222", "#fff", "#000080"]);

  // Create a size scale for bubbles on top right. Watch out: must be a rootscale!
  var size = d3.scaleSqrt()
    .domain([0, 1])
    .range([0, 9]);

  // X scale
  var x = d3.scalePoint()
    .range([0, width])
    .domain(domain)

  // Y scale
  var y = d3.scalePoint()
    .range([0, height])
    .domain(domain)

  // Create one 'g' element for each cell of the correlogram
  var cor = svg.selectAll(".cor")
    .data(data)
    .enter()
    .append("g")
      .attr("class", "cor")
      .attr("transform", function(d) {
        return "translate(" + x(d.x) + "," + y(d.y) + ")";
      });

  // Low left part + Diagonal: Add the text with specific color
  cor
    .filter(function(d){
      var ypos = domain.indexOf(d.y);
      var xpos = domain.indexOf(d.x);
      return xpos <= ypos;
    })
    .append("text")
      .attr("y", 5)
      .text(function(d) {
        if (d.x === d.y) {
          return d.x;
        } else {
          return d.value.toFixed(2);
        }
      })
      .style("font-size", 11)
      .style("text-align", "center")
      .style("fill", function(d){
        if (d.x === d.y) {
          return "#000";
        } else {
          return color(d.value);
        }
      });


  // Up right part: add circles
  cor
    .filter(function(d){
      var ypos = domain.indexOf(d.y);
      var xpos = domain.indexOf(d.x);
      return xpos > ypos;
    })
    .append("circle")
      .attr("r", function(d){ return size(Math.abs(d.value)) })
      .style("fill", function(d){
        if (d.x === d.y) {
          return "#000";
        } else {
          return color(d.value);
        }
      })
      .style("opacity", 0.8)

})

</script>

Related blocks →

  • Correlogram - link