Clustered Interactive Force Layout v4

This clustered bubble force graph shows college majors by size, grouped by major category. This is an extension of Shan Carter's Clustered Force Layout 4.0. The data is was found in FiveThirtyEight's College Majors data set in their Data Repo.

<!doctype html>
<meta charset="utf-8">
<style type="text/css">
  div.tooltip { 
    position: absolute;     
    text-align: center;     
    width: 150px;          
    /*height: 28px;         */
    padding: 2px;       
    font: 12px sans-serif;    
    background: lightgrey; 
    border: 0px;    
    border-radius: 8px;     
    pointer-events: none;     
  }
</style>
<body>
<script src="//d3js.org/d3.v4.min.js"></script>
<script>

let margin = {top: 100, right: 100, bottom: 100, left: 100};

let width = 960,
    height = 500,
    padding = 1.5, // separation between same-color circles
    clusterPadding = 6, // separation between different-color circles
    maxRadius = height*0.1;

let n = 200, // total number of nodes
    m = 10, // number of distinct clusters
    z = d3.scaleOrdinal(d3.schemeCategory20),
    clusters = new Array(m);

let svg = d3.select('body')
    .append('svg')
    .attr('height', height)
    .attr('width', width)
    .append('g').attr('transform', 'translate(' + width / 2 + ',' + height / 2 + ')');

// Define the div for the tooltip
let div = d3.select("body").append("div") 
    .attr("class", "tooltip")       
    .style("opacity", 0);

//load college major data
d3.csv("college-majors.csv", function(d){
  let radiusScale = d3.scaleLinear()
    .domain(d3.extent(d, function(d) { return +d.Total;} ))
    .range([4, maxRadius]);

console.log(radiusScale(300000));

let nodes = d.map((d) => {
    // scale radius to fit on the screen
    let scaledRadius  = radiusScale(+d.Total),
        forcedCluster = +d.Major_category_code;

// add cluster id and radius to array
    d = {
      cluster     : forcedCluster,
      r           : scaledRadius,
      major       : d.Major,
      major_cat   : d.Major_category
    };
    // add to clusters array if it doesn't exist or the radius is larger than another radius in the cluster
    if (!clusters[forcedCluster] || (scaledRadius > clusters[forcedCluster].r)) clusters[forcedCluster] = d;

return d;
  });

// append the circles to svg then style
  // add functions for interaction
  let circles = svg.append('g')
        .datum(nodes)
      .selectAll('.circle')
        .data(d => d)
      .enter().append('circle')
        .attr('r', (d) => d.r)
        .attr('fill', (d) => z(d.cluster))
        .attr('stroke', 'black')
        .attr('stroke-width', 1)
        .call(d3.drag()
            .on("start", dragstarted)
            .on("drag", dragged)
            .on("end", dragended))
        // add tooltips to each circle
        .on("mouseover", function(d) {
            div.transition()    
                .duration(200)    
                .style("opacity", .9);    
            div .html( "The major " + d.major+ "<br/>In the category " + d.major_cat )  
                .style("left", (d3.event.pageX) + "px")   
                .style("top", (d3.event.pageY - 28) + "px");  
            })          
        .on("mouseout", function(d) {   
            div.transition()    
                .duration(500)    
                .style("opacity", 0); 
        });

// create the clustering/collision force simulation
  let simulation = d3.forceSimulation(nodes)
      .velocityDecay(0.2)
      .force("x", d3.forceX().strength(.0005))
      .force("y", d3.forceY().strength(.0005))
      .force("collide", collide)
      .force("cluster", clustering)
      .on("tick", ticked);

function ticked() {
      circles
          .attr('cx', (d) => d.x)
          .attr('cy', (d) => d.y);
  }

// Drag functions used for interactivity
  function dragstarted(d) {
    if (!d3.event.active) simulation.alphaTarget(0.3).restart();
    d.fx = d.x;
    d.fy = d.y;
  }

function dragged(d) {
    d.fx = d3.event.x;
    d.fy = d3.event.y;
  }

function dragended(d) {
    if (!d3.event.active) simulation.alphaTarget(0);
    d.fx = null;
    d.fy = null;
  }

// These are implementations of the custom forces.
  function clustering(alpha) {
      nodes.forEach(function(d) {
        var cluster = clusters[d.cluster];
        if (cluster === d) return;
        var x = d.x - cluster.x,
            y = d.y - cluster.y,
            l = Math.sqrt(x * x + y * y),
            r = d.r + cluster.r;
        if (l !== r) {
          l = (l - r) / l * alpha;
          d.x -= x *= l;
          d.y -= y *= l;
          cluster.x += x;
          cluster.y += y;
        }
      });
  }

function collide(alpha) {
    var quadtree = d3.quadtree()
        .x((d) => d.x)
        .y((d) => d.y)
        .addAll(nodes);

nodes.forEach(function(d) {
      var r = d.r + maxRadius + Math.max(padding, clusterPadding),
          nx1 = d.x - r,
          nx2 = d.x + r,
          ny1 = d.y - r,
          ny2 = d.y + r;
      quadtree.visit(function(quad, x1, y1, x2, y2) {

if (quad.data && (quad.data !== d)) {
          var x = d.x - quad.data.x,
              y = d.y - quad.data.y,
              l = Math.sqrt(x * x + y * y),
              r = d.r + quad.data.r + (d.cluster === quad.data.cluster ? padding : clusterPadding);
          if (l < r) {
            l = (l - r) / l * alpha;
            d.x -= x *= l;
            d.y -= y *= l;
            quad.data.x += x;
            quad.data.y += y;
          }
        }
        return x1 > nx2 || x2 < nx1 || y1 > ny2 || y2 < ny1;
      });
    });
  }

});
</script>

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