Interactive pie chart with input data selector in d3.js

Steps:

Warning: are you sure you want to use a pie chart? Learn why it is not recommended.

Visit the button section to learn how to build the input selector that triggers a function.

Visit the interactivity section to learn about smooth transition in general.

Note: transition could be improved to avoid the current weird shape distortion. The code would be way more complicated though, see here for an example.

<!DOCTYPE html>
<meta charset="utf-8">

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

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

<!-- Add 2 buttons -->
<button onclick="update(data1)">Data 1</button>
<button onclick="update(data2)">Data 2</button>

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

<script>

// set the dimensions and margins of the graph
var width = 450
    height = 450
    margin = 40

// The radius of the pieplot is half the width or half the height (smallest one). I subtract a bit of margin.
var radius = Math.min(width, height) / 2 - margin

// append the svg object to the div called 'my_dataviz'
var svg = d3.select("#my_dataviz")
  .append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

// create 2 data_set
var data1 = {a: 9, b: 20, c:30, d:8, e:12}
var data2 = {a: 6, b: 16, c:20, d:14, e:19, f:12}

// set the color scale
var color = d3.scaleOrdinal()
  .domain(["a", "b", "c", "d", "e", "f"])
  .range(d3.schemeDark2);

// A function that create / update the plot for a given variable:
function update(data) {

  // Compute the position of each group on the pie:
  var pie = d3.pie()
    .value(function(d) {return d.value; })
    .sort(function(a, b) { console.log(a) ; return d3.ascending(a.key, b.key);} ) // This make sure that group order remains the same in the pie chart
  var data_ready = pie(d3.entries(data))

  // map to data
  var u = svg.selectAll("path")
    .data(data_ready)

  // Build the pie chart: Basically, each part of the pie is a path that we build using the arc function.
  u
    .enter()
    .append('path')
    .merge(u)
    .transition()
    .duration(1000)
    .attr('d', d3.arc()
      .innerRadius(0)
      .outerRadius(radius)
    )
    .attr('fill', function(d){ return(color(d.data.key)) })
    .attr("stroke", "white")
    .style("stroke-width", "2px")
    .style("opacity", 1)

  // remove the group that is not present anymore
  u
    .exit()
    .remove()

}

// Initialize the plot with the first dataset
update(data1)

</script>

Steps:

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