force directed graph in D3.js (v4)

Force-directed layout of UKfaculty graph (from R package "igraphdata") in D3.js v4

based on Mike Bostock's code here: https://bl.ocks.org/mbostock/4062045

<!DOCTYPE html>
<meta charset="utf-8">
<style>
  /* colors based on R: brewer.pal(4, "Set1")
  "#E41A1C"
  "#377EB8"
  "#4DAF4A"
  "#984EA3" */

.links line {
    stroke: #999;
    stroke-opacity: 0.6;
  }

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

body {
    font-family: sans-serif;
  }
</style>

var filename = 'UKfaculty.json';
  var vSize = 7; // vertex size

// decide on a color scheme
  var color = d3.scaleOrdinal(d3.schemeCategory10);
  // list of colors based on colorbrewer instead

var weight = d3.scaleLinear()
    .domain([0, 30])
    .range([0, 3]);

// set up the simulation
  // a force simulation with links, charge, and a force that keeps the graph centered
  var simulation = d3.forceSimulation()
    .force("link", d3.forceLink().id(function(d) {
      return d.id;
    }))
    .force("charge", d3.forceManyBody().strength(-120))
    .force("center", d3.forceCenter(width / 2, height / 2));

d3.json(filename, function(error, graph) {
    if (error) throw error;

// fix json naming
    graph.nodes = graph.vertices;
    delete graph.vertices;

graph.links = graph.edges;
    delete graph.edges;

console.log(graph);
    console.log(graph.links);
    console.log(graph.nodes);

graph.nodes.forEach(function(d, i) {
      d.id = (i + 1).toString();
      // 1 indexed source R
    })

// fix source and to fields
    graph.links.forEach(function(d, i) {
      d.source = d.from.toString();
      d.target = d.to.toString();
    })

var link = svg.append("g")
      .attr("class", "links")
      .selectAll("line")
      .data(graph.links)
      .enter()
      .append("line")
      .attr("stroke-width", function(d) {
        return weight(d.weight);
      });

var node = svg.append("g")
      .attr("class", "nodes")
      .selectAll("circle")
      .data(graph.nodes)
      .enter().append("circle")
      .attr("r", vSize)
      .attr("fill", function(d) {
        return color(d.Group);
      })
      .on('mouseover', function(d) {
        vertex = d.id; // counter, index
        group = d.Group;
        theColor = color(d.Group);

//console.log( d.Group);

d3.select("#node")
          .text("v: " + vertex + ", group: " + group)
          .style("color", theColor)
      })
      .on('mouseout', function(d) {
        d3.select("#vertex")
          .text("")
      })
      .call(d3.drag()
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));

// set up simulation
    simulation
      .nodes(graph.nodes)
      .on("tick", ticked);

simulation
      .force("link")
      .links(graph.links);

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

// make it dynamic

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;
  }
</script>

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