Line plot with dropdown to filter group in d3.js




This post describes how to smoothly transition between groups in a line chart with d3.js. It is very close from this other example. Here groups values are stored in the same column instead of having one distinct column each. It is the tidy or long format versus the previous wide or untidy format.


Line chart section

Steps:

  • First, you need to understand how to build a basic line chart.

  • Here the input dataset is composed by several columns: one per group.

  • Chart is initialized using the first group.

  • Then a update() function is created. It smoothly transforms the chart with the value of another column

  • This function is triggered whenever the select button is changed.
<!DOCTYPE html>
<meta charset="utf-8">

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

<!-- Initialize a select button -->
<select id="selectButton"></select>

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

<!-- Color Scale -->
<script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script>


<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/data_to_viz/master/Example_dataset/5_OneCatSevNumOrdered.csv", function(data) {

    // List of groups (here I have one group per column)
    var allGroup = d3.map(data, function(d){return(d.name)}).keys()

    // add the options to the button
    d3.select("#selectButton")
      .selectAll('myOptions')
     	.data(allGroup)
      .enter()
    	.append('option')
      .text(function (d) { return d; }) // text showed in the menu
      .attr("value", function (d) { return d; }) // corresponding value returned by the button

    // A color scale: one color for each group
    var myColor = d3.scaleOrdinal()
      .domain(allGroup)
      .range(d3.schemeSet2);

    // Add X axis --> it is a date format
    var x = d3.scaleLinear()
      .domain(d3.extent(data, function(d) { return d.year; }))
      .range([ 0, width ]);
    svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x).ticks(7));

    // Add Y axis
    var y = d3.scaleLinear()
      .domain([0, d3.max(data, function(d) { return +d.n; })])
      .range([ height, 0 ]);
    svg.append("g")
      .call(d3.axisLeft(y));

    // Initialize line with first group of the list
    var line = svg
      .append('g')
      .append("path")
        .datum(data.filter(function(d){return d.name==allGroup[0]}))
        .attr("d", d3.line()
          .x(function(d) { return x(d.year) })
          .y(function(d) { return y(+d.n) })
        )
        .attr("stroke", function(d){ return myColor("valueA") })
        .style("stroke-width", 4)
        .style("fill", "none")

    // A function that update the chart
    function update(selectedGroup) {

      // Create new data with the selection?
      var dataFilter = data.filter(function(d){return d.name==selectedGroup})

      // Give these new data to update line
      line
          .datum(dataFilter)
          .transition()
          .duration(1000)
          .attr("d", d3.line()
            .x(function(d) { return x(d.year) })
            .y(function(d) { return y(+d.n) })
          )
          .attr("stroke", function(d){ return myColor(selectedGroup) })
    }

    // When the button is changed, run the updateChart function
    d3.select("#selectButton").on("change", function(d) {
        // recover the option that has been chosen
        var selectedOption = d3.select(this).property("value")
        // run the updateChart function with this selected option
        update(selectedOption)
    })

})


</script>

Related blocks →