D3.js force directed graph, each group different color?

Question

I've made a force directed graph with d3.js plugin, and I wanna color the nodes and the labels with the different color according to group which they belong.

I've added scale for color:

var color = d3.scale.category20();

and to node variable I've added:

.style("fill", function(d) { return color(d.group); })

but all nodes are in the same color..

Here is my current situation: http://jsfiddle.net/WBkw9/

full script:

var links = [
  {source: "John", target: "Mike", group: "5"},
  {source: "John", target: "Janice", group: "5"},
  {source: "John", target: "Caleb", group: "5"},
  {source: "John", target: "Anna", group: "4"},
  {source: "John", target: "Tommy", group: "3"},
  {source: "John", target: "Jack", group: "2"},
  {source: "John", target: "Vilma", group: "1"},
];

var nodes = {};

// Compute the distinct nodes from the links.
links.forEach(function(link) {
  link.source = nodes[link.source] || (nodes[link.source] = {name: link.source});
  link.target = nodes[link.target] || (nodes[link.target] = {name: link.target});
});

var color = d3.scale.category20();

var width = 960,
    height = 500;

var force = d3.layout.force()
    .nodes(d3.values(nodes))
    .links(links)
    .size([width, height])
    .linkDistance(60)
    .charge(-300)
    .on("tick", tick)
    .start();

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

var link = svg.selectAll(".link")
    .data(force.links())
  .enter().append("line")
    .attr("class", "link");

var node = svg.selectAll(".node")
    .data(force.nodes())
  .enter().append("g")
    .attr("class", "node")
    .style("fill", function(d) { return color(d.group); })
    .on("mouseover", mouseover)
    .on("mouseout", mouseout)
    .call(force.drag);

node.append("circle")
    .attr("r", 8);

node.append("text")
    .attr("x", 12)
    .attr("dy", ".35em")
    .text(function(d) { return d.name; });

function tick() {
  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("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; });
}

function mouseover() {
  d3.select(this).select("circle").transition()
      .duration(750)
      .attr("r", 16);
}

function mouseout() {
  d3.select(this).select("circle").transition()
      .duration(750)
      .attr("r", 8);
}

what am I missing for different color on each group?

Answer 1

Your problem is that group is not defined for your data. As a result, all of your nodes are colored for group 'undefined'. Your circles are defined for the data in force.nodes(), which have the attributes index name px py weight x and y. group is only defined for the links, which never have color applied to them.

As it currently stands, there also isn't a clear way to determine what color a node should be. What happens if more than one link connects to a node, and these links are in different groups?