[D3] Build a Scatter Plot with D3 v4

Scatter plots, sometimes also known as bubble charts, are another common type of visualization. They’re extremely versatile thanks to their ability to display multiple dimensions of data simultaneously using x and y position, opacity, color, and even shape. This lesson introduces the SVG circle element as part of building a robust scatter plot.

var margin = {
    top: 10,
    right: 20,
    bottom: 65,
    left: 40
};
var width = 400 - margin.left - margin.right;
var height = 600 - margin.top - margin.bottom;

var svg = d3.select('.chart')
    .append('svg')
    .attr('width', width + margin.left + margin.right)
    .attr('height', height + margin.top + margin.bottom)
    .call(responsivefy)
    .append('g')
    .attr('transform', 'translate(' + margin.left + ', ' + margin.top + ')');

/**
 * Load data
 */
d3.json('../data/data2.json', function (err, data) {
    /**
     * Add Y axis
     */
    var yScale = d3.scaleLinear()
        .domain(d3.extent(data, (d) => d.expectancy))
        .range([height, 0])
        .nice();
    var yAxis = d3.axisLeft(yScale);
    svg.call(yAxis);

    /**
     * Add X axis
     */
    var xScale = d3.scaleLinear()
        .domain(d3.extent(data, d => d.cost))
        .range([0, width])
        .nice();

    var xAxis = d3.axisBottom(xScale);
    svg
        .append('g')
        .attr('transform', `translate(0, ${height})`)
        .call(xAxis);

    // For circle, we need scaleSqrt
    var rScale = d3.scaleSqrt()
        .domain([0, d3.max(data, d => d.population)])
        .range([0, 40]);

    // Create some container to contain the circles
    var circles = svg.selectAll('.ball')
        .data(data)
        .enter()
        .append('g')
        .attr('class', 'ball')
        .attr('transform', d => {
            return `translate(${xScale(d.cost)}, ${yScale(d.expectancy)})`
        });

    // Add circle to each containers
    circles
        .append('circle')
        .attr('cx', 0)
        .attr('cy', 0)
        .attr('r', d => rScale(d.population))
        .style('opacity', 0.5)
        .style('fill', 'steelblue');

    // Add text
    circles
        .append('text')
        .style('text-anchor', 'middle')
        .style('fill', 'black')
        .attr('y', 4)
        .text(d => d.code)
});

function responsivefy(svg) {
    // get container + svg aspect ratio
    var container = d3.select(svg.node().parentNode),
        width = parseInt(svg.style("width")),
        height = parseInt(svg.style("height")),
        aspect = width / height;

    // add viewBox and preserveAspectRatio properties,
    // and call resize so that svg resizes on inital page load
    svg.attr("viewBox", "0 0 " + width + " " + height)
        .attr("preserveAspectRatio", "xMinYMid")
        .call(resize);

    // to register multiple listeners for same event type,
    // you need to add namespace, i.e., 'click.foo'
    // necessary if you call invoke this function for multiple svgs
    // api docs: https://github.com/mbostock/d3/wiki/Selections#on
    d3.select(window).on("resize." + container.attr("id"), resize);

    // get width of container and resize svg to fit it
    function resize() {
        var targetWidth = parseInt(container.style("width"));
        svg.attr("width", targetWidth);
        svg.attr("height", Math.round(targetWidth / aspect));
    }
}