D3 Examples - Building a radial hierarchy from a flat table

Building a radial hierarchy from a flat table
A test block to experiment with building hierarchies from flat files. Pretty messy at the moment.
The flatToHierarchy() function transforms a flat and wide table into a hierarchy based on a sequence of field names. Adapted from this Stack Overflow answer.
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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>
<meta charset="utf-8">
<style>
    body {text-align:center}
    svg { font-family: Courier;}
  .node circle {
  fill: #999;
}
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.node text {
  font: 10px sans-serif;
}
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.node--internal circle {
  fill: #555;
  stroke: #222;
}
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.node--internal text {
  text-shadow: 0 1px 0 #fff, 0 -1px 0 #fff, 1px 0 0 #fff, -1px 0 0 #fff;
}
​
.link {
  fill: none;
  stroke: #555;
  stroke-opacity: 0.4;
  stroke-width: 1.5px;
}
</style>
<body>
<svg width="1060" height="1060"></svg>
  
    
<script src="https://d3js.org/d3.v4.min.js"></script>
  
<script>
const svg   = d3.select("svg"),
        width = +svg.attr("width"),
        height= +svg.attr("height"),
      margin= 20,
      max_radius = 20,
      max_value = 4000,
      g = svg.append("g").attr("transform", "translate(" + (width / 2 + 40) + "," + (height / 2 + 90) + ")"),
      // Plantae, Fungi, Protozoa,Chromista
            kingdom = 'Plantae'
​
// Declare a D3 layout
const tree = d3.tree()
    .size([2 * Math.PI, 400])
    .separation(function(a, b) { return (a.parent == b.parent ? 1 : 2) / a.depth; })
​
// Load our external data
d3.csv("data.csv", function(data) {
  //var data = data.filter( (d) => d.kingdom == kingdom)
  
  data.sort(function(x, y){return d3.descending(+x.described, +y.described)})
  
  var fineData = []
  data.forEach(function(d){
    if (+d.adventive > 0) {
      var item = Object.assign({}, d)
      item['type'] = 'adventive'
      item['itemCount'] = +d.adventive
      fineData.push(item)
    }
    if ((+d.described - +d.adventive - +d.endemic_species) > 0) {
      var item = Object.assign({}, d)
      item['type'] = 'native'
      item['itemCount'] = +d.described - +d.adventive - +d.endemic_species
      fineData.push(item)
    }
    if (+d.endemic_species > 0) {
      var item = Object.assign({}, d)
      item['type'] = 'endemic'
      item['itemCount'] = +d.endemic_species
      fineData.push(item)
    }
  })
   
  
  // Build our hierarchy from a series of levels
  // change/reorder the level elements for a different tree
  const levels = ["kingdom", "phylum_common", "taxon"],
        root = flatToHierarchy(fineData, levels, 'type', 'itemCount')
  
 
  // Draw on screen
  var link = g.selectAll(".link")
    .data(tree(root).links())
    .enter().append("path")
      .attr("class", "link")
      .attr("d", d3.linkRadial()
          .angle(function(d) { return d.x; })
          .radius(function(d) { return d.y; }))
  
  var node = g.selectAll(".node")
    .data(tree(root).descendants())
    .enter().append("g")
      //.attr("class", function(d) { return "node" + (d.children ? " node--internal" : " node--leaf"); })
        .style("fill", function(d) {
        if (d.children) {return '#888'}
        //console.log(d.data.type)
        if (d.data.type == 'adventive') {return 'red'}
        if (d.data.type == 'native') {return 'blue'}
        if (d.data.type == 'endemic') {return 'green'}
      })
      .attr("transform", function(d) { return "translate(" + radialPoint(d.x, d.y) + ")"; })
  
  node.append("circle")
      .attr('r', (d) => radius(d.value))
  /*
  node.append("text")
      .attr("dy", "0.31em")
      .attr("x", function(d) { return d.x < Math.PI === !d.children ? 6 : -6; })
      .attr("text-anchor", function(d) { return d.x < Math.PI === !d.children ? "start" : "end"; })
      .attr("transform", function(d) { return "rotate(" + (d.x < Math.PI ? d.x - Math.PI / 2 : d.x + Math.PI / 2) * 180 / Math.PI + ")"; })
      .text(function(d) { return d.children ? d.data.name : ''})*/
  
})
​
​
​
//
//
// Helper function for converting flat data to a hierarchy
// with a name and count field on each node.
// TODO - probably shouldn't name the value field "count"
​
function radius(val) {
  return Math.sqrt(val / max_value) * max_radius
}
​
function radialPoint(x, y) {
  return [(y = +y) * Math.cos(x -= Math.PI / 2), y * Math.sin(x)];
}
​
function flatToHierarchy(flatData, levels, nameField, countField) {
  // Adapted from https://stackoverflow.com/a/19317823
  var nestedData = { name :"root", children : [] }
  
  // For each data row, loop through the expected levels traversing the output tree
  flatData.forEach(function(d){
      // Keep this as a reference to the current level
      var depthCursor = nestedData.children;
      // Go down one level at a time
      levels.forEach(function( property, depth ){
​
          // See if a branch has already been created
          var index;
          depthCursor.forEach(function(child,i){
              if ( d[property] == child.name ) index = i;
          });
          // Add a branch if it isn't there
          if ( isNaN(index) ) {
              depthCursor.push({ name : d[property], children : []});
              index = depthCursor.length - 1;
          }
          // Reference the new child array as we go deeper into the tree
          depthCursor = depthCursor[index].children;
          // This is a leaf, so add last element to specified branch
          if ( depth === levels.length - 1 ) {
            depthCursor.push({
              'name':d[nameField],
              'count':+d[countField],
              'type':d.type /// TODO - generic way to add fields
            });
          } 
      })
  })
  
  // sum up the leaves / branches and return the hierarchy
  return d3.hierarchy(nestedData).sum(function(d){ return d.count; })
  
}
  
</script>
</body>
</html>
    