Correlogram with scatterplot in d3.js

Steps:

First of all, you need to understand how to build a scatterplot with d3.js.

The idea here is to create one scatterplot for each pair of variable. Then this scatterplot is translated to a specific position on the grid.

In the diagonal, the name of the variable is written

Note that the X and Y limits of each axis are adapted to each variable. It would be easy to fix it to a specific value for all.

<!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>

// Dimension of the whole chart. Only one size since it has to be square
var marginWhole = {top: 10, right: 10, bottom: 10, left: 10},
    sizeWhole = 640 - marginWhole.left - marginWhole.right

// Create the svg area
var svg = d3.select("#my_dataviz")
  .append("svg")
    .attr("width", sizeWhole  + marginWhole.left + marginWhole.right)
    .attr("height", sizeWhole  + marginWhole.top + marginWhole.bottom)
  .append("g")
    .attr("transform", "translate(" + marginWhole.left + "," + marginWhole.top + ")");


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

  // What are the numeric variables in this dataset? How many do I have
  var allVar = ["Sepal_Length", "Sepal_Width", "Petal_Length", "Petal_Width"]
  var numVar = allVar.length

  // Now I can compute the size of a single chart
  mar = 20
  size = sizeWhole / numVar


  // ----------------- //
  // Scales
  // ----------------- //

  // Create a scale: gives the position of each pair each variable
  var position = d3.scalePoint()
    .domain(allVar)
    .range([0, sizeWhole-size])

  // Color scale: give me a specie name, I return a color
  var color = d3.scaleOrdinal()
    .domain(["setosa", "versicolor", "virginica" ])
    .range([ "#402D54", "#D18975", "#8FD175"])


  // ------------------------------- //
  // Add charts
  // ------------------------------- //
  for (i in allVar){
    for (j in allVar){

      // Get current variable name
      var var1 = allVar[i]
      var var2 = allVar[j]

      // If var1 == var2 i'm on the diagonal, I skip that
      if (var1 === var2) { continue; }

      // Add X Scale of each graph
      xextent = d3.extent(data, function(d) { return +d[var1] })
      var x = d3.scaleLinear()
        .domain(xextent).nice()
        .range([ 0, size-2*mar ]);

      // Add Y Scale of each graph
      yextent = d3.extent(data, function(d) { return +d[var2] })
      var y = d3.scaleLinear()
        .domain(yextent).nice()
        .range([ size-2*mar, 0 ]);

      // Add a 'g' at the right position
      var tmp = svg
        .append('g')
        .attr("transform", "translate(" + (position(var1)+mar) + "," + (position(var2)+mar) + ")");

      // Add X and Y axis in tmp
      tmp.append("g")
        .attr("transform", "translate(" + 0 + "," + (size-mar*2) + ")")
        .call(d3.axisBottom(x).ticks(3));
      tmp.append("g")
        .call(d3.axisLeft(y).ticks(3));

      // Add circle
      tmp
        .selectAll("myCircles")
        .data(data)
        .enter()
        .append("circle")
          .attr("cx", function(d){ return x(+d[var1]) })
          .attr("cy", function(d){ return y(+d[var2]) })
          .attr("r", 3)
          .attr("fill", function(d){ return color(d.Species)})
    }
  }


  // ------------------------------- //
  // Add variable names = diagonal
  // ------------------------------- //
  for (i in allVar){
    for (j in allVar){
      // If var1 == var2 i'm on the diagonal, otherwisee I skip
      if (i != j) { continue; }
      // Add text
      var var1 = allVar[i]
      var var2 = allVar[j]
      svg
        .append('g')
        .attr("transform", "translate(" + position(var1) + "," + position(var2) + ")")
        .append('text')
          .attr("x", size/2)
          .attr("y", size/2)
          .text(var1)
          .attr("text-anchor", "middle")

    }
  }


})

</script>

Steps:

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