eturn d.id; }))
    .force("charge", d3.forceManyBody().strength(function() { return -100; }))
    .force("center", d3.forceCenter(width / 2, height / 2));


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

d3.json("./groups/dist2/group-58.json", function(error, graph) {
  if (error) throw error;

  var link = svg.append("g")
      .attr("class", "links")
    .selectAll("line")
    .data(graph.links)
    .enter().append("lin