StackOverflow: radial tidy tree with networkx data

Converting data from the python networkx graph manipulation library into a d3 hierarchy.

For Stack Overflow question how to use d3.js to visualise a json tree graph

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

.node circle {
  fill: #999;
}

.node text {
  font: 10px sans-serif;
}

.node--internal circle {
  fill: #555;
}

.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>
</head>
<body>
<svg width="960" height="1060"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height"),
    g = svg.append("g").attr("transform", "translate(" + (width / 2 + 40) + ",400)");

var tree = d3.tree()
    .size([2 * Math.PI, 300])
    .separation(function(a, b) { return (a.parent == b.parent ? 1 : 2) / a.depth; });

d3.json("data.json", function(error, data) {
  if (error) throw error;

var root = tree(d3.hierarchy(data));

var link = g.selectAll(".link")
    .data(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(root.descendants())
    .enter().append("g")
      .attr("class", function(d) { return "node" + (d.children ? " node--internal" : " node--leaf"); })
      .attr("transform", function(d) { return "translate(" + radialPoint(d.x, d.y) + ")"; });

node.append("circle")
      .attr("r", 2.5);

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.data.id
  		});
});

function radialPoint(x, y) {
  return [(y = +y) * Math.cos(x -= Math.PI / 2), y * Math.sin(x)];
}

</script>
</body>
</html>

https://d3js.org/d3.v4.min.js