'Coloring Connected Components D3 V3

I am working in D3 version 3, and I have a simple working program that can read a JSON file and convert it into an animated, linked graph.

I was wondering if there was a way for me to color separate connected components differently, for example, have the first component colored blue and another colored red, in a way that could be applied to a larger JSON file. I am pretty new to javascript, but wondering if I could use the group id to determine a node's color. I organized my example JSON file as follows-

{
    "nodes":[
        {"name":"node1","group":1},
        {"name":"node2","group":1},
        {"name":"node3","group":1},
        {"name":"node4","group":3}
    ],
    "links":[
        {"source":2,"target":1,"weight":3},
        {"source":0,"target":2,"weight":3}
    ]
}

Note that each node is part of a group (connected component).

My index.html is as follows.

<!DOCTYPE html>
<meta charset="utf-8">
<script src="https://d3js.org/d3.v3.min.js"></script>
<style>

    svg {
        background-color:red;
        width: 100%;
    }

    .link {
        stroke: #fff;
    }

    .node text {
        stroke:#fff;
        fill: aliceblue;
        cursor: pointer;
        font-family: fantasy;
        padding: 10%;
    }

    .node circle{
        stroke:#fff;
        stroke-width:3px;
        fill:#fff;
        padding: 20px;
    }

</style>
<body>

  <div class="nodeContainer">

    <script>

    var width = 960,
        height = 500

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

    var force = d3.layout.force()
        .gravity(.05)
        .distance(100)
        .charge(-100)
        .size([width, height]);

    d3.json("graphFile.json", function(json) {
    force
        .nodes(json.nodes)
        .links(json.links)
        .start();

    var link = svg.selectAll(".link")
        .data(json.links)
        .enter().append("line")
        .attr("class", "link")
        .style("stroke-width", function(d) { return Math.sqrt(d.weight); });

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

    node.append("circle")
        .attr("r","20");

    node.append("text")
        .attr("dx", 23)
        .attr("dy", ".35em")
        .text(function(d) { return d.name });

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

    </script>

  </div>
javascriptcssd3.js


Solution 1:[1]

Here are a few approaches to color the nodes based on the group:

  1. Using a pre-defined d3 colorScale (d3 oridnal color schemas)

    var colorScale = d3.scale.category10().domain(json.nodes.map(function(d) { return d.group; }));

  2. User defined ordinal color scale:

    var colorScale = d3.scale.ordinal().domain([1, 2, 3]).range(["blue", "green", "red"]);

  3. If the extent of the groups is huge, I'd recommend a linear scale using a gradient of colors. Similar to this: http://bl.ocks.org/jfreyre/b1882159636cc9e1283a

Using one of the above and applying to the nodes:

node.append("circle")
 .attr("r","20")
 .style('fill', function(d) {
    return colorScale(d.group);
 });

Here's a snippet:

var json = {
"nodes":[
    {"name":"node1","group":1},
    {"name":"node2","group":1},
    {"name":"node3","group":1},
    {"name":"node4","group":3}
],
"links":[
    {"source":2,"target":1,"weight":3},
    {"source":0,"target":2,"weight":3}
]
};

var width = 960,
    height = 500

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

var force = d3.layout.force()
    .gravity(.05)
    .distance(100)
    .charge(-100)
    .size([width, height]);

var colorScale = d3.scale.category10().domain(json.nodes.map(function(d) { return d.group; }));
//var colorScale = d3.scale.ordinal().domain([1, 2, 3]).range(["blue", "green", "red"]);

force
    .nodes(json.nodes)
    .links(json.links)
    .start();

var link = svg.selectAll(".link")
    .data(json.links)
    .enter().append("line")
    .attr("class", "link")
    .style("stroke-width", function(d) { return Math.sqrt(d.weight); });

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

node.append("circle")
    .attr("r","20")
    .style('fill', function(d) {
    	return colorScale(d.group);
    });

node.append("text")
    .attr("dx", 23)
    .attr("dy", ".35em")
    .text(function(d) { return d.name });

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("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; });
});
svg {
    background-color:red;
    width: 100%;
    }

.link {
stroke: #fff;
}

.node text {
stroke:#fff;
fill: aliceblue;
cursor: pointer;
font-family: fantasy;
padding: 10%;
}

.node circle{
stroke:#fff;
stroke-width:3px;
fill:#fff;
padding: 20px;
}
<script src="https://d3js.org/d3.v3.min.js"></script>

<div class="nodeContainer">
</div>

Hope this helps.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Shashank

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