Force Directed Graph Toggle to Circle

Based on Mike Bostock's force-directed graph example showing character co-occurence in Les Misérables, this gist shows how to toggle between the animated force-directed graph and a circle formation akin to a chord diagram.

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

#controls {
  position: absolute;
  width: 940px;
  padding: 10px;
  z-index: 1;
}

.node {
  stroke: #fff;
  stroke-width: 1.5px;
}

.link {
  stroke: #999;
}

</style>
<body>
<div id="controls">
  <input name="mode" type="radio" value="force" id="mode-force" checked>
  <label for="mode-force"> Force-Directed</label>
  <input name="mode" type="radio" value="circle" id="mode-circle">
  <label for="mode-circle"> Circle</label>
</div>
<div id="graph"></div>

var width = 960,
    height = 500,
    margin = 100;
    
var x_center = width / 2,
    y_center = height / 2,
    radius = (height - 2 * margin) / 2;

var n_elements;
function index_to_rad(index) {
  return 2 * Math.PI * index / n_elements;
}

var color = d3.scale.category20();

var force = d3.layout.force()
    .charge(-120)
    .linkDistance(30)
    .size([width, height]);

var x_scale = d3.scale.linear()
    .domain([0,1])
    .range([x_center, x_center + radius]);

var y_scale = d3.scale.linear()
    .domain([0,1])
    .range([y_center, y_center + radius]);

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

d3.json("miserables.json", function(error, graph) {
  if (error) throw error;
  
  graph.nodes = graph.nodes.sort(function(a, b) { return d3.ascending(a.group, b.group); });
  n_elements = graph.nodes.length;

force
      .nodes(graph.nodes)
      .links(graph.links)
      .start();

var max_value = d3.max(graph.links, function(d){ return d.value; });

var link = svg.selectAll(".link")
      .data(graph.links)
    .enter().append("line")
      .attr("class", "link")
      .style("opacity", function(d) { return 0.2 + 0.8 * d.value / max_value; });

var node = svg.selectAll(".node")
      .data(graph.nodes)
    .enter().append("circle")
      .attr("class", "node")
      .attr("r", 5)
      .style("fill", function(d) { return color(d.group); })
      .call(force.drag);

node.append("title")
      .text(function(d) { return d.name; });

force.on("tick", function() {
    link.attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });

node.attr("cx", function(d) { return d.x; })
        .attr("cy", function(d) { return d.y; });
  });

d3.selectAll("#controls input[name=mode]").on("change", function(){
    if (this.value == 'circle') {

force.stop();

} else {

svg.selectAll('line')
        .transition().duration(1000)
          .attr('x1', function(d){ return d.source.x_resume; })
          .attr('y1', function(d){ return d.source.y_resume; })
          .attr('x2', function(d){ return d.target.x_resume; })
          .attr('y2', function(d){ return d.target.y_resume; });

svg.selectAll('circle')
        .transition().duration(1000)
          .attr('cx', function(d){ return d.x_resume; })
          .attr('cy', function(d){ return d.y_resume; });

setTimeout(function(){
        force.resume();
      },1000);

}

});

</script>

https://d3js.org/d3.v3.min.js