Visualizing time dependent networks with d3.js

For a change, here is a post about data visualization. The other day I was thinking about a way of visualizing a time-dependent network in d3.js and in this post I will show a prototype solution.

And there it is, the solution:

As you can see, there is a time slider that allows you to visualize the graph as a function of time. The width of each edge gives information about the strength of the connection between two nodes, the size of each node represents how important a particular node is in a given year.

You can drag the nodes around for a little bit of fun and hovering over each node will tell you the id of the node.

Here is the code that is used to generate the graph (vizgraph.html)

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<!DOCTYPE html>
<meta charset="utf-8">
<link rel="stylesheet" href="vizstyle.css"/>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>
<script>
var svg = d3.select("svg"),
width = +svg.attr("width"),
height = +svg.attr("height"),
color = d3.scaleOrdinal(d3.schemeCategory10);
/////// SLIDER ///////
var L = 10;
var slider_size = 0.75*width;
var left_margin = 0.5*(width - slider_size);
var x = d3.scaleLinear()
.domain([0,10])
.range([left_margin, slider_size + left_margin])
.clamp(true);
var slider = svg.append("g")
.attr("transform", "translate(15,"+(height-50)+")");
slider.append("line")
.attr("class", "track")
.attr("x1", x.range()[0])
.attr("x2", x.range()[1])
.select(function() { return this.parentNode.appendChild(this.cloneNode(true)); })
.attr("class", "track-inset")
.select(function() { return this.parentNode.appendChild(this.cloneNode(true)); })
.attr("class", "track-overlay")
.call(d3.drag()
.on("start.interrupt", function() { slider.interrupt(); })
.on("start drag", function() { return hue(x.invert(d3.event.x)); }));
var years = d3.range(2010,2016,1)
var dx = L/(years.length-1)
var xticks = d3.range(0,L+dx,dx)
slider.insert("g", ".track-overlay")
.attr("class", "ticks")
.attr("transform", "translate(0," + 25 + ")")
.selectAll("text")
.data(xticks)
.enter().append("text")
.attr("x", x)
.attr("text-anchor", "middle")
.text(function(d,i) { return years[i]; });
var handle = slider.insert("circle", ".track-overlay")
.attr("class", "handle")
.attr("r", 9)
.attr("cx", x.range()[0]); //initial position to zero
function hue(h) {
handle.attr("cx", x(h));
}
function dragstarted(d) {
if (!d3.event.active) simulation.alphaTarget(0).restart();
d.fx = d.x;
d.fy = d.y;
}
function dragged(d) {
d.fx = d3.event.x;
d.fy = d3.event.y;
}
function dragended(d) {
if (!d3.event.active) simulation.alphaTarget(0);
d.fx = null;
d.fy = null;
}
/////// GRAPH ////////
d3.json("graph.json", function(error, graph) {
if (error) throw error;
//user-defined parameters
var maxDistance = 300, //max distance between two nodes
minDistance = 10, //min distance betwween two nodes
maxRadius = 30, //max radius of circle
minRadius = 8, //min radius of circle
minLinkwidth = 0, //min width of link
maxLinkwidth = 6 //max width of link
var [maxConnect, maxFraction] = getnetworkProp(graph);
var nodes = graph.nodes,
nodeById = d3.map(nodes, function(d) { return d.id; }),
links = graph.links,
value = links.map(function(d){return d.value}),
l = []
links.forEach(function(link) {
var s = nodeById.get(link.source),
t = nodeById.get(link.target),
v = link.value,
y = link.year;
l.push({source: s, target: t, year: y, value:v});
});
links = l
simulation = d3.forceSimulation(nodes)
simulation.force("charge", d3.forceManyBody())
.force("link", d3.forceLink(links))
.on("tick", ticked);
var g = svg.append("g").attr("transform", "translate(" + width / 2 + "," + 0.45 * height + ")"),
link = g.append("g").attr("stroke", "#000").attr("stroke-width", 1.5).selectAll(".link"),
node = g.append("g").attr("stroke", "#fff").attr("stroke-width", 1.5).selectAll(".node");
restart();
d3.interval(function() {
restart();
},150)
function restart() {
var current_year = years[Math.round(x.invert(jQuery(".handle").attr("cx"))/dx)];
//get "radius" of each node for current_year
var fraction = graph.nodes.map(function(d) {return d.fraction}).map(function(d) {return d[current_year.toString()];})
// Apply the general update pattern to the nodes.
node = node.data(nodes, function(d) { return d.id;});
node.exit().remove();
node = node.enter().append("circle")
.attr("class","node")
.attr("fill", function(d) { return color(d.id); })
.merge(node)
.call(d3.drag()
.on("start", dragstarted)
.on("drag", dragged)
.on("end", dragended));
node.append("title")
.text(function(d) { return d.id; });
//apply transition to radii of nodes
node.transition()
.duration(50)
.attr("r",function(d) {return Math.max(minRadius,d.fraction[current_year.toString()]/maxFraction * maxRadius);})
// Apply the general update pattern to the links
links_filtered = links.filter(function(d) {return d.year==current_year;});
link = link.data(links_filtered, function(d) { return d.source.id + "-" + d.target.id; });
link.exit().remove();
link = link.enter()
.append("line")
.attr("class", "link")
.merge(link);
//define transition to width of edges
link.transition()
.duration(50)
.attr("stroke-width", function(d,i) { return Math.max(minLinkwidth,d.value/maxConnect * maxLinkwidth);})
// Update and restart the simulation.
simulation.nodes(nodes);
simulation.force("link").links(links)
simulation.force("link", d3.forceLink(links)
.distance(function(d) {
if(d.year==current_year){
return Math.min(maxConnect/d.value * minDistance,maxDistance);
}
else{
return maxDistance;
}})
)
simulation.alpha(0.4).restart();
}
//this function defines position of nodes and links
//at each "simulation time step"
function ticked() {
node.attr("cx", function(d) { return d.x; })
.attr("cy", function(d) { return d.y; })
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; });
}
})
//this function calculates properties of network
//(i.e., max connection between nodes, max fraction value of node)
function getnetworkProp(graph){
//1) max connection between nodes
var maxConnect = Math.max.apply(Math,graph.links.map(function(d) {return d.value;})); //max connection between nodes
//2) max fraction value (used to draw nodes radii)
var maxFraction = 0;
var arr, obj, maxf;
for (i=0;i<graph.nodes.length;i++){
obj = graph.nodes[i].fraction
arr = Object.keys( obj ).map(function (key) { return obj[key]; });
maxf = Math.max.apply( null, arr );
maxFraction = Math.max(maxFraction,maxf);
}
return [maxConnect, maxFraction];
}
</script>

Two more things are missing: the css file and the data file.

Let’s first start with the css file (vizstyle.css)

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.node {
cursor: pointer;
}
.link {
fill: none;
stroke: #8b8b8b;
}
.ticks {
font: 12px sans-serif;
fill: black;
}
.track,
.track-inset,
.track-overlay {
stroke-linecap: round;
}
.track {
stroke: #000;
stroke-opacity: 0.3;
stroke-width: 10px;
}
.track-inset {
stroke: #ddd;
stroke-width: 8px;
}
.track-overlay {
pointer-events: stroke;
stroke-width: 50px;
cursor: pointer;
}
.handle {
fill: #fff;
stroke: #000;
stroke-opacity: 0.5;
stroke-width: 1.25px;
}

And finally the json file used to generate the graph (graph.json)

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{
"nodes": [
{"id": "A","fraction":{"2010":0.2,"2011":0.05,"2012":0.1,"2013":0.03,"2014":0.1,"2015":0.02}},
{"id": "B","fraction":{"2010":0.08,"2011":0.07,"2012":0.02,"2013":0.03,"2014":0.1,"2015":0.2}},
{"id": "C","fraction":{"2010":0.12,"2011":0.04,"2012":0.2,"2013":0.02,"2014":0.4,"2015":0.02}},
{"id": "D","fraction":{"2010":0.1,"2011":0.05,"2012":0.02,"2013":0.01,"2014":0.1,"2015":0.03}},
{"id": "E","fraction":{"2010":0.1,"2011":0.4,"2012":0.02,"2013":0.01,"2014":0.1,"2015":0.03}}
],
"links": [
{"source": "A", "target": "B", "value": 30, "year":2010},
{"source": "A", "target": "C", "value": 20, "year":2010},
{"source": "A", "target": "D", "value": 7,"year":2010},
{"source": "A", "target": "E", "value": 3,"year":2010},
{"source": "B", "target": "C", "value": 0,"year":2010},
{"source": "B", "target": "D", "value": 7,"year":2010},
{"source": "B", "target": "E", "value": 3,"year":2010},
{"source": "C", "target": "D", "value": 10,"year":2010},
{"source": "C", "target": "E", "value": 3,"year":2010},
{"source": "D", "target": "E", "value": 7,"year":2010},
{"source": "A", "target": "B", "value": 15, "year":2011},
{"source": "A", "target": "C", "value": 17, "year":2011},
{"source": "A", "target": "D", "value": 1,"year":2011},
{"source": "A", "target": "E", "value": 3,"year":2011},
{"source": "B", "target": "C", "value": 3,"year":2011},
{"source": "B", "target": "D", "value": 9,"year":2011},
{"source": "B", "target": "E", "value": 3,"year":2011},
{"source": "C", "target": "D", "value": 22,"year":2011},
{"source": "C", "target": "E", "value": 10,"year":2011},
{"source": "D", "target": "E", "value": 0,"year":2011},
{"source": "A", "target": "B", "value": 4, "year":2012},
{"source": "A", "target": "C", "value": 3, "year":2012},
{"source": "A", "target": "D", "value": 3,"year":2012},
{"source": "A", "target": "E", "value": 8,"year":2012},
{"source": "B", "target": "C", "value": 10,"year":2012},
{"source": "B", "target": "D", "value": 40,"year":2012},
{"source": "B", "target": "E", "value": 23,"year":2012},
{"source": "C", "target": "D", "value": 3,"year":2012},
{"source": "C", "target": "E", "value": 30,"year":2012},
{"source": "D", "target": "E", "value": 16,"year":2012},
{"source": "A", "target": "E", "value": 8,"year":2012},
{"source": "A", "target": "B", "value": 4, "year":2013},
{"source": "A", "target": "C", "value": 6, "year":2013},
{"source": "A", "target": "D", "value": 7,"year":2013},
{"source": "A", "target": "E", "value": 12,"year":2013},
{"source": "B", "target": "C", "value": 0,"year":2013},
{"source": "B", "target": "D", "value": 11,"year":2013},
{"source": "B", "target": "E", "value": 12,"year":2013},
{"source": "C", "target": "D", "value": 0,"year":2013},
{"source": "C", "target": "E", "value": 20,"year":2013},
{"source": "D", "target": "E", "value": 18,"year":2013},
{"source": "A", "target": "B", "value": 10, "year":2014},
{"source": "A", "target": "C", "value": 10, "year":2014},
{"source": "A", "target": "D", "value": 22,"year":2014},
{"source": "A", "target": "E", "value": 22,"year":2014},
{"source": "B", "target": "C", "value": 2,"year":2014},
{"source": "B", "target": "D", "value": 2,"year":2014},
{"source": "B", "target": "E", "value": 26,"year":2014},
{"source": "C", "target": "D", "value": 4,"year":2014},
{"source": "C", "target": "E", "value": 22,"year":2014},
{"source": "D", "target": "E", "value": 28,"year":2014},
{"source": "A", "target": "B", "value": 18, "year":2015},
{"source": "A", "target": "C", "value": 0, "year":2015},
{"source": "A", "target": "D", "value": 40,"year":2015},
{"source": "A", "target": "E", "value": 40,"year":2015},
{"source": "B", "target": "C", "value": 9,"year":2015},
{"source": "B", "target": "D", "value": 3,"year":2015},
{"source": "B", "target": "E", "value": 40,"year":2015},
{"source": "C", "target": "D", "value": 15,"year":2015},
{"source": "C", "target": "E", "value": 7,"year":2015},
{"source": "D", "target": "E", "value": 11,"year":2015}
]
}