Parallel coordinates chart with color effect




This post is an extension of the previous basic parallel coordinate chart. The idea is to add a color scale to highlight the different groups and hover effects to highlight a specific group or a particular axis


Parallel coordinates section

Steps:

  • You probably want to understand the previous basic parallel coordinate chart first.

  • Here hover effects are triggered following 2 different strategies:
    • axis: pure css - axis have a specific class called axis. It is possible to specify a style when hovering with axis:hover
    • groups: use javascript - a function is triggered when a group is hovered, another when group is not hovered anymore.
<!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>

<!-- A bit of style -->
<style>
.axis {
  opacity: 0.4;
}
.axis:hover {
  opacity: 1;
}
</style>


<script>

// set the dimensions and margins of the graph
var margin = {top: 30, right: 50, bottom: 10, left: 50},
  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 + ")");

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

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

  // Here I set the list of dimension manually to control the order of axis:
  dimensions = ["Petal_Length", "Petal_Width", "Sepal_Length", "Sepal_Width"]

  // For each dimension, I build a linear scale. I store all in a y object
  var y = {}
  for (i in dimensions) {
    name = dimensions[i]
    y[name] = d3.scaleLinear()
      .domain( [0,8] ) // --> Same axis range for each group
      // --> different axis range for each group --> .domain( [d3.extent(data, function(d) { return +d[name]; })] )
      .range([height, 0])
  }

  // Build the X scale -> it find the best position for each Y axis
  x = d3.scalePoint()
    .range([0, width])
    .domain(dimensions);

  // Highlight the specie that is hovered
  var highlight = function(d){

    selected_specie = d.Species

    // first every group turns grey
    d3.selectAll(".line")
      .transition().duration(200)
      .style("stroke", "lightgrey")
      .style("opacity", "0.2")
    // Second the hovered specie takes its color
    d3.selectAll("." + selected_specie)
      .transition().duration(200)
      .style("stroke", color(selected_specie))
      .style("opacity", "1")
  }

  // Unhighlight
  var doNotHighlight = function(d){
    d3.selectAll(".line")
      .transition().duration(200).delay(1000)
      .style("stroke", function(d){ return( color(d.Species))} )
      .style("opacity", "1")
  }

  // The path function take a row of the csv as input, and return x and y coordinates of the line to draw for this raw.
  function path(d) {
      return d3.line()(dimensions.map(function(p) { return [x(p), y[p](d[p])]; }));
  }

  // Draw the lines
  svg
    .selectAll("myPath")
    .data(data)
    .enter()
    .append("path")
      .attr("class", function (d) { return "line " + d.Species } ) // 2 class for each line: 'line' and the group name
      .attr("d",  path)
      .style("fill", "none" )
      .style("stroke", function(d){ return( color(d.Species))} )
      .style("opacity", 0.5)
      .on("mouseover", highlight)
      .on("mouseleave", doNotHighlight )

  // Draw the axis:
  svg.selectAll("myAxis")
    // For each dimension of the dataset I add a 'g' element:
    .data(dimensions).enter()
    .append("g")
    .attr("class", "axis")
    // I translate this element to its right position on the x axis
    .attr("transform", function(d) { return "translate(" + x(d) + ")"; })
    // And I build the axis with the call function
    .each(function(d) { d3.select(this).call(d3.axisLeft().ticks(5).scale(y[d])); })
    // Add axis title
    .append("text")
      .style("text-anchor", "middle")
      .attr("y", -9)
      .text(function(d) { return d; })
      .style("fill", "black")

})


</script>

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