How to put labels on the edges in the Dendrogram example?

Question

Given a tree diagram like the Dendrogram example (source), how would one put labels on the edges? The JavaScript code to draw the edges looks like the next lines:

var link = vis.selectAll("path.link")
    .data(cluster.links(nodes))
  .enter().append("path")
    .attr("class", "link")
    .attr("d", diagonal);

Homosexuality

Answer 1

Mike Bostock, the author of D3, very graciously helped with the following solution. Define a style for g.link; I just copied the style for g.node. Then I replaced the "var link =...." code with the following. The x and y functions place the label in the center of the path.

var linkg = vis.selectAll("g.link")
    .data(cluster.links(nodes))
    .enter().append("g")
    .attr("class", "link");

linkg.append("path")
    .attr("class", "link")
    .attr("d", diagonal);

linkg.append("text")
    .attr("x", function(d) { return (d.source.y + d.target.y) / 2; })
    .attr("y", function(d) { return (d.source.x + d.target.x) / 2; })
    .attr("text-anchor", "middle")
    .text(function(d) {
        return "edgeLabel";
    });

The text function should ideally provide a label specifically for each edge. I populated an object with the names of my edges while preparing my data, so my text function looks like this:

    .text(function(d) {
        var key = d.source.name + ":" + d.target.name;
        return edgeNames[key];
    });

Homosexuality

A few people have been tempted to swap the x's and y's in the second and third lines of the linkg.append("text") piece. Please don't, they are correct as they are. There is an update because the Dendrogram example on the D3 website has changed. The first line should now read: var linkg = svg.selectAll(".link") – Homosexuality