Graph with Threshold Slider

Based on Mike Bostock's force-directed graph example showing character co-occurence in Les Misérables, this gist shows how to implement a dynamic link-display threshold. (The slider is based on Bostock's "brush as slider" block.) See this blog post on bilateral migration for an example use case.

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

.node {
  stroke: #fff;
  stroke-width: 1.5px;
}

.link {
  stroke: #999;
  stroke-opacity: .6;
}

.axis {
  opacity: 0.5;
  font: 10px sans-serif;
  -webkit-user-select: none;
  -moz-user-select: none;
  user-select: none;
}

.axis .domain {
  fill: none;
  stroke: #000;
  stroke-opacity: .3;
  stroke-width: 4px;
  stroke-linecap: round;
}

.axis .halo {
  fill: none;
  stroke: #ddd;
  stroke-width: 3px;
  stroke-linecap: round;
}

.slider .handle {
  fill: #fff;
  stroke: #000;
  stroke-opacity: .5;
  stroke-width: 1.25px;
  cursor: grab;
}

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

var width = 960,
    height = 500;

var color = d3.scale.category20();

var force = d3.layout.force()
    .charge(-120)
    .linkDistance(30)
    .size([width, height]);

var x = d3.scale.linear()
    .domain([0, 20])
    .range([250, 80])
    .clamp(true);

var brush = d3.svg.brush()
    .y(x)
    .extent([0, 0]);

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

var links_g = svg.append("g");

var nodes_g = svg.append("g");

svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(" + (width - 20)  + ",0)")
    .call(d3.svg.axis()
      .scale(x)
      .orient("left")
      .tickFormat(function(d) { return d; })
      .tickSize(0)
      .tickPadding(12))
  .select(".domain")
  .select(function() { return this.parentNode.appendChild(this.cloneNode(true)); })
    .attr("class", "halo");

var slider = svg.append("g")
    .attr("class", "slider")
    .call(brush);

slider.selectAll(".extent,.resize")
    .remove();

var handle = slider.append("circle")
    .attr("class", "handle")
    .attr("transform", "translate(" + (width - 20) + ",0)")
    .attr("r", 5);

svg.append("text")
    .attr("x", width - 15)
    .attr("y", 60)
    .attr("text-anchor", "end")
    .attr("font-size", "12px")
    .style("opacity", 0.5)
    .text("co-occurence threshold")

d3.json("miserables.json", function(error, graph) {
  if (error) throw error;
  
  graph.links.forEach(function(d,i){ d.i = i; });

link.enter().append("line")
        .attr("class", "link")
        .style("stroke-width", function(d) { return Math.sqrt(d.value); });

link.exit().remove();

force.on("tick", function() {
      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("cx", function(d) { return d.x; })
          .attr("cy", function(d) { return d.y; });
    });

force.start();

}
    
  force
      .nodes(graph.nodes);

var node = nodes_g.selectAll(".node")
      .data(graph.nodes)
    .enter().append("circle")
      .attr("class", "node")
      .attr("r", 5)
      .style("fill", function(d) { return color(d.group); })
      .call(force.drag);

node.append("title")
      .text(function(d) { return d.name; });

brush.on("brush", brushed);

slider
    .call(brush.extent([5, 5]))
    .call(brush.event);

});

</script>

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