Multi-line graph 3: Legend by d3noob

This is a derivative of the simple d3.js graph used as an example in the book D3 Tips and Tricks. The stock data was sourced from Mike Bostock’s small multiples example.

It is the third graph in a series that is building a multi-line graph that incorperates an automatically developed legend and a system that can toggle the lines off and on as desired.

This version is demonstrating the addition of a legend to the graph.

The graph should be taken in context with the text of the book which can be downloaded for free from Leanpub.

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style> /* set the CSS */

body { font: 12px Arial;}

path { 
    stroke: steelblue;
    stroke-width: 2;
    fill: none;
}

.axis path,
.axis line {
    fill: none;
    stroke: grey;
    stroke-width: 1;
    shape-rendering: crispEdges;
}

.legend {
    font-size: 16px;
    font-weight: bold;
    text-anchor: middle;
}

</style>
<body>

<!-- load the d3.js library -->    
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js"></script>

<script>

// Set the dimensions of the canvas / graph
var margin = {top: 30, right: 20, bottom: 70, left: 50},
    width = 600 - margin.left - margin.right,
    height = 300 - margin.top - margin.bottom;

// Parse the date / time
var parseDate = d3.time.format("%b %Y").parse;

// Set the ranges
var x = d3.time.scale().range([0, width]);
var y = d3.scale.linear().range([height, 0]);

// Define the axes
var xAxis = d3.svg.axis().scale(x)
    .orient("bottom").ticks(5);

var yAxis = d3.svg.axis().scale(y)
    .orient("left").ticks(5);

// Define the line
var priceline = d3.svg.line()	
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.price); });
    
// Adds the svg canvas
var svg = d3.select("body")
    .append("svg")
        .attr("width", width + margin.left + margin.right)
        .attr("height", height + margin.top + margin.bottom)
    .append("g")
        .attr("transform", 
              "translate(" + margin.left + "," + margin.top + ")");

// Get the data
d3.csv("stocks.csv", function(error, data) {
    data.forEach(function(d) {
		d.date = parseDate(d.date);
		d.price = +d.price;
    });

    // Scale the range of the data
    x.domain(d3.extent(data, function(d) { return d.date; }));
    y.domain([0, d3.max(data, function(d) { return d.price; })]);

    // Nest the entries by symbol
    var dataNest = d3.nest()
        .key(function(d) {return d.symbol;})
        .entries(data);

    var color = d3.scale.category10();   // set the colour scale

    legendSpace = width/dataNest.length; // spacing for legend

    // Loop through each symbol / key
    dataNest.forEach(function(d,i) { 

        svg.append("path")
            .attr("class", "line")
            .style("stroke", function() { // Add the colours dynamically
                return d.color = color(d.key); })
            .attr("d", priceline(d.values));

        // Add the Legend
        svg.append("text")
            .attr("x", (legendSpace/2)+i*legendSpace) // spacing
            .attr("y", height + (margin.bottom/2)+ 5)
            .attr("class", "legend")    // style the legend
            .style("fill", function() { // dynamic colours
                return d.color = color(d.key); })
            .text(d.key);

    });

    // Add the X Axis
    svg.append("g")
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height + ")")
        .call(xAxis);

    // Add the Y Axis
    svg.append("g")
        .attr("class", "y axis")
        .call(yAxis);

});

</script>
</body>