empty_load.html

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

    .axis--y path {
        display: none;
    }

    .cities {
        fill: none;
        stroke: #aaa;
        stroke-linejoin: round;
        stroke-linecap: round;
        stroke-width: 1.5px;
    }

    .city--hover {
        stroke: #000;
    }

    .focus text {
        text-anchor: middle;
        text-shadow: 0 1px 0 #fff, 1px 0 0 #fff, 0 -1px 0 #fff, -1px 0 0 #fff;
    }

    .voronoi path {
        fill: none;
        pointer-events: all;
    }

    .voronoi--show path {
        stroke: red;
        stroke-opacity: 0.2;
    }

    #form {
        position: absolute;
        top: 20px;
        right: 30px;
    }
</style>
<svg width="960" height="500"></svg>
<label id="form" for="show-voronoi">
    Show Voronoi
    <input type="checkbox" id="show-voronoi" disabled>
</label>
<script src="//d3js.org/d3.v4.min.js"></script>
<script>

    var xs = [];

    var svg = d3.select("svg"),
        margin = { top: 20, right: 30, bottom: 30, left: 40 },
        width = svg.attr("width") - margin.left - margin.right,
        height = svg.attr("height") - margin.top - margin.bottom,
        g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
    var x = d3.scaleLinear()
        .domain([0, 200])
        .range([0, width]);

    var y = d3.scaleLinear()
        .range([height, 0]);

    var voronoi = d3.voronoi()
        .x(function (d) { return x(d.date); })
        .y(function (d) { return y(d.value); })
        .extent([[-margin.left, -margin.top], [width + margin.right, height + margin.bottom]]);

    var line = d3.line()
        .x(function (d) { return x(d.date); })
        .y(function (d) { return y(d.value); });

    d3.csv("unemployment.csv").get(function (error, input_data) {
        var data = [];
        input_data.columns.slice(1)
            .forEach(e => xs.push(+e));
        
        input_data.forEach(function (d) {
            var c = { name: d.name, values: null };
            c.values = [];

            xs.forEach(function (k, i) {
                c.values.push(
                    { city: c, date: xs[i], value: +d[k] }
                );
            });
            data.push(c);
        });

        x.domain(d3.extent(xs));
        y.domain([0, d3.max(data, function (c) { return d3.max(c.values, function (d) { return d.value; }); })]).nice();

        g.append("g")
            .attr("class", "axis axis--x")
            .attr("transform", "translate(0," + height + ")")
            .call(d3.axisBottom(x));

        g.append("g")
            .attr("class", "axis axis--y")
            .call(d3.axisLeft(y).ticks(10))
            .append("text")
            .attr("x", 4)
            .attr("y", 0.5)
            .attr("dy", "0.32em")
            .style("text-anchor", "start")
            .style("fill", "#000")
            .style("font-weight", "bold")
            .text("Unemployment Rate");

        g.append("g")
            .attr("class", "cities")
            .selectAll("path")
            .data(data)
            .enter().append("path")
            .attr("d", function (d) { d.line = this; return line(d.values); });

        var focus = g.append("g")
            .attr("transform", "translate(-100,-100)")
            .attr("class", "focus");

        focus.append("circle")
            .attr("r", 3.5);

        focus.append("text")
            .attr("y", -10);

        var voronoiGroup = g.append("g")
            .attr("class", "voronoi");

        voronoiGroup.selectAll("path")
            .data(voronoi.polygons(d3.merge(data.map(function (d) { return d.values; }))))
            .enter().append("path")
            .attr("d", function (d) { return d ? "M" + d.join("L") + "Z" : null; })
            .on("mouseover", mouseover)
            .on("mouseout", mouseout);

        d3.select("#show-voronoi")
            .property("disabled", false)
            .on("change", function () { voronoiGroup.classed("voronoi--show", this.checked); });

        function mouseover(d) {
            console.log("d", d);
            console.log("d.data", d.data);
            d3.select(d.data.city.line).classed("city--hover", true);
            d.data.city.line.parentNode.appendChild(d.data.city.line);
            focus.attr("transform", "translate(" + x(d.data.date) + "," + y(d.data.value) + ")");
            focus.select("text").text(d.data.city.name);
        }

        function mouseout(d) {
            d3.select(d.data.city.line).classed("city--hover", false);
            focus.attr("transform", "translate(-100,-100)");
        }

    });
</script>