Grouped scatterplot in d3.js




This post describes how to build a grouped scatter plot with d3.js. It follows the previous basic scatterplot. It extends it by adding a color scale linked with a categoric variable: each group will thus appear with a different color on the chart.


Scatterplot section

Steps:

  • Extension of the previous most basic scatterplot

  • A color scale is created with scaleOrdinal, attributing a different color for each group. See more about color scale here.

  • This color scale is then called when the fill style of circles is set.

  • Next step: add interactivity to it to highlight a specific group on hover.
<!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>

// set the dimensions and margins of the graph
var margin = {top: 10, right: 30, bottom: 30, left: 60},
    width = 460 - margin.left - margin.right,
    height = 400 - margin.top - margin.bottom;

// 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(" + margin.left + "," + margin.top + ")");

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

  // Add X axis
  var x = d3.scaleLinear()
    .domain([4, 8])
    .range([ 0, width ]);
  svg.append("g")
    .attr("transform", "translate(0," + height + ")")
    .call(d3.axisBottom(x));

  // Add Y axis
  var y = d3.scaleLinear()
    .domain([0, 9])
    .range([ height, 0]);
  svg.append("g")
    .call(d3.axisLeft(y));

  // Color scale: give me a specie name, I return a color
  var color = d3.scaleOrdinal()
    .domain(["setosa", "versicolor", "virginica" ])
    .range([ "#440154ff", "#21908dff", "#fde725ff"])

  // Add dots
  svg.append('g')
    .selectAll("dot")
    .data(data)
    .enter()
    .append("circle")
      .attr("cx", function (d) { return x(d.Sepal_Length); } )
      .attr("cy", function (d) { return y(d.Petal_Length); } )
      .attr("r", 5)
      .style("fill", function (d) { return color(d.Species) } )

})

</script>

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