force_brush.js

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

var color = d3.scaleOrdinal(d3.schemeCategory20);

var simulation = d3.forceSimulation()
    .force("link", d3.forceLink().id(function(d) { return d.id; }))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));

d3.json("miserables.json", function(error, graph) {
    if (error) throw error;

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

    var node = svg.append("g")
        .attr("class", "nodes")
        .selectAll("circle")
        .data(graph.nodes)
        .enter().append("circle")
        .attr("r", 5)
        .attr("fill", function(d) { return color(d.group); })
        .attr("fill-copied", function(d) { return color(d.group); })
        .call(d3.drag()
            .on("start", dragstarted)
            .on("drag", dragged)
            .on("end", dragended));

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

    simulation
        .nodes(graph.nodes)
        .on("tick", ticked);

    simulation.force("link")
        .links(graph.links);


    var brush = svg.append("g")
        .datum(function() { return {selected: false, previouslySelected: false}; })
        .attr("class", "brush")
        .call(d3.brush()
            .extent([[0, 0], [width, height]])
            .on("brush", function() {
                var extent = d3.event.selection;
                node.style("fill", function(d) {
                    var evaluation = extent[0][0] <= d.x && d.x < extent[1][0]
                        && extent[0][1] <= d.y && d.y < extent[1][1];
                    if (evaluation == true) {
                        return "red"
                    } else {
                        return d3.select(this).attr("fill-copied");
                    }

                });
            })
    );

    function ticked() {
        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; });
    }
});

function dragstarted(d) {
    if (!d3.event.active) simulation.alphaTarget(0.3).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;
}