D3 Examples - Networks

Networks - Edges 6

Rather than representing directionality of each edge, it might make more sense to represent whether a tie is reciprocated, which is a product of directionality. Reciprocity indicates stronger ties and might be more important to an audience than explicit direction of connections.

The method for calculating reciprocity is simply to create a hash of edge IDs and check when each is evaluated to see if the reverse of that edge has already been added to the array.

Obviously, this should also have a legend, because every data visualization should have a legend.

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<html>
<head>
  <title>Drawing reciprocal edges</title>
  <meta charset="utf-8" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
</head>
<style>
  svg {
    height: 500px;
    width: 500px;
    border: 1px solid gray;
  }
</style>
<body>
​
<div id="viz">
  <svg>
  </svg>
</div>
</body>
  <footer>
<script>
​
d3.csv("firm.csv",function(error,data) {createNetwork(data)});
​
function createNetwork(edgelist) {
  var nodeHash = {};
  var edgeHash = {};
  var nodes = [];
  var edges = [];
​
  edgelist.forEach(function (edge) {
    if (!nodeHash[edge.source]) {
      nodeHash[edge.source] = {id: edge.source, label: edge.source};
      nodes.push(nodeHash[edge.source]);
    }
    if (!nodeHash[edge.target]) {
      nodeHash[edge.target] = {id: edge.target, label: edge.target};
      nodes.push(nodeHash[edge.target]);
    }
​
    //is it reciprocal?
​
    if (edge.weight >= 5) {
      if (edgeHash[edge.target + "-" + edge.source]) {
        edgeHash[edge.target + "-" + edge.source].reciprocal = true;
      }
      else {
        var newEdge = {source: nodeHash[edge.source], target: nodeHash[edge.target], weight: edge.weight};
        edgeHash[edge.source + "-" + edge.target] = newEdge;
        edges.push(newEdge);
      }
    }
  });
  createForceNetwork(nodes, edges);
}
​
function createForceNetwork(nodes, edges) {
​
//create a network from an edgelist
​
  var force = d3.layout.force().nodes(nodes).links(edges)
  .size([500,500])
  .charge(-200)
  .on("tick", updateNetwork);
​
  d3.select("svg").selectAll("line")
  .data(edges)
  .enter()
  .append("line")
  .style("stroke-width", "2px")
  .style("stroke", function (d) {return d.reciprocal ? "#66CCCC" : "#996666"});
​
  d3.select("svg").selectAll("circle")
  .data(nodes)
  .enter()
  .append("circle")
  .style("fill", "#FFFF99")
  .style("stroke", "#666633")
  .style("stroke-width", "1px")
  .attr("r", 5)
  .call(force.drag());
​
  force.start();
​
  function updateNetwork() {
    d3.select("svg").selectAll("line")
      .attr("x1", function (d) {return d.source.x})
      .attr("x2", function (d) {return d.target.x})
      .attr("y1", function (d) {return d.source.y})
      .attr("y2", function (d) {return d.target.y});
​
    d3.select("svg").selectAll("circle")
      .attr("cx", function (d) {return d.x})
      .attr("cy", function (d) {return d.y});
  }
​
​
​
}
</script>
  </footer>
​
</html>
​
    