Force layout graph with colour-coded node neighbours.

First attempt at making a colour-coded graph, with code snippets inspired from the D3 community.

Green => Friend and follower.

Red => Follower

Blue => Friend.

Improvements needed:

Smooth transition on the arrow head.
Better positioning of the arrow heads.

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

.node circle {
  stroke: white;
  stroke-width: 1.5px;
  opacity: 1.0;
}

line {
  stroke: black;
  stroke-width: 1.5px;
  stroke-opacity: 1.0;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.js"></script>
<script>

data = {
          nodes: [
                  {size: 10},
                  {size: 5},
                  {size: 2},
                  {size: 3},
                  {size: 30},
                  {size: 40}
                  ],
        links: [
                  {source: 0,target: 1},
                  {source: 0,target: 2},
                  {source: 1,target: 0},
                  {source: 3,target: 0},
                  {source: 4,target: 1}
                ]
        }

var mouseOverFunction = function(d) {
  var circle = d3.select(this);

node
    .transition(500)
      .style("opacity", function(o) {
        return isConnected(o, d) ? 1.0 : 0.2 ;
      })
      .style("fill", function(o) {
        if (isConnectedAsTarget(o, d) && isConnectedAsSource(o, d) ) {
          fillcolor = 'green';
        } else if (isConnectedAsSource(o, d)) {
          fillcolor = 'red';
        } else if (isConnectedAsTarget(o, d)) {
          fillcolor = 'blue';
        } else if (isEqual(o, d)) {
          fillcolor = "hotpink";
        } else {
          fillcolor = '#000';
        }
        return fillcolor;
      });

link
    .transition(500)
      .style("stroke-opacity", function(o) {
        return o.source === d || o.target === d ? 1 : 0.2;
      })
      .transition(500)
      .attr("marker-end", function(o) {
        return o.source === d || o.target === d ? "url(#arrowhead)" : "url()";
      });

circle
    .transition(500)
      .attr("r", function(){ return 1.4 * node_radius(d)});
}

var mouseOutFunction = function() {
  var circle = d3.select(this);

node
    .transition(500);

link
    .transition(500);

circle
    .transition(500)
      .attr("r", node_radius);
}

function isConnected(a, b) {
    return isConnectedAsTarget(a, b) || isConnectedAsSource(a, b) || a.index == b.index;
}

function isConnectedAsSource(a, b) {
    return linkedByIndex[a.index + "," + b.index];
}

function isConnectedAsTarget(a, b) {
    return linkedByIndex[b.index + "," + a.index];
}

function isEqual(a, b) {
    return a.index == b.index;
}

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

function node_radius(d) { return Math.pow(40.0 * d.size, 1/3); }

var width = 1000;
var height = 500;

var nodes = data.nodes
var links = data.links

var force = d3.layout.force()
              .nodes(nodes)
              .links(links)
              .charge(-3000)
              .friction(0.6)
              .gravity(0.6)
              .size([width,height])
              .start();

var linkedByIndex = {};
links.forEach(function(d) {
  linkedByIndex[d.source.index + "," + d.target.index] = true;
});

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

var link = svg.selectAll("line")
              .data(links)
            .enter().append("line")

var node = svg.selectAll(".node")
              .data(nodes)
            .enter().append("g")
              .attr("class", "node")
              .call(force.drag);

node
  .append("circle")
  .attr("r", node_radius)
  .on("mouseover", mouseOverFunction)
  .on("mouseout", mouseOutFunction);

svg
  .append("marker")
  .attr("id", "arrowhead")
  .attr("refX", 6 + 7) // Controls the shift of the arrow head along the path
  .attr("refY", 2)
  .attr("markerWidth", 6)
  .attr("markerHeight", 4)
  .attr("orient", "auto")
  .append("path")
    .attr("d", "M 0,0 V 4 L6,2 Z");

link
  .attr("marker-end", "url()");

force
  .on("tick",tick);

</script>
</body>

Modified http://d3js.org/d3.v3.js to a secure url

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