d3.js line graph with dual Y axes by d3noob

index.html

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

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;
}

</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js"></script>

<script>

var margin = {top: 30, right: 40, bottom: 30, left: 50},
    width = 600 - margin.left - margin.right,
    height = 270 - margin.top - margin.bottom;

var parseDate = d3.time.format("%d-%b-%y").parse;

var x = d3.time.scale().range([0, width]);
var y0 = d3.scale.linear().range([height, 0]);
var y1 = d3.scale.linear().range([height, 0]);

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

var yAxisLeft = d3.svg.axis().scale(y0)
    .orient("left").ticks(5);

var yAxisRight = d3.svg.axis().scale(y1)
    .orient("right").ticks(5); 

var valueline = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y0(d.close); });
    
var valueline2 = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y1(d.open); });
  
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("data2a.csv", function(error, data) {
    data.forEach(function(d) {
        d.date = parseDate(d.date);
        d.close = +d.close;
        d.open = +d.open;
    });

    // Scale the range of the data
    x.domain(d3.extent(data, function(d) { return d.date; }));
    y0.domain([0, d3.max(data, function(d) {
		return Math.max(d.close); })]); 
    y1.domain([0, d3.max(data, function(d) { 
		return Math.max(d.open); })]);

    svg.append("path")        // Add the valueline path.
        .attr("d", valueline(data));

    svg.append("path")        // Add the valueline2 path.
        .style("stroke", "red")
        .attr("d", valueline2(data));

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

    svg.append("g")
        .attr("class", "y axis")
        .style("fill", "steelblue")
        .call(yAxisLeft);	

    svg.append("g")				
        .attr("class", "y axis")	
        .attr("transform", "translate(" + width + " ,0)")	
        .style("fill", "red")		
        .call(yAxisRight);

});

</script>
</body>

data2a.csv

date,close,open
1-May-12,58.13,3.41
30-Apr-12,53.98,4.55
27-Apr-12,67.00,6.78
26-Apr-12,89.70,7.85
25-Apr-12,99.00,8.92
24-Apr-12,130.28,9.92
23-Apr-12,166.70,10.13
20-Apr-12,234.98,12.23
19-Apr-12,345.44,13.45
18-Apr-12,443.34,16.04
17-Apr-12,543.70,18.03
16-Apr-12,580.13,21.02
13-Apr-12,605.23,22.34
12-Apr-12,622.77,20.15
11-Apr-12,626.20,21.26
10-Apr-12,628.44,31.04
9-Apr-12,636.23,35.04
5-Apr-12,633.68,41.02
4-Apr-12,624.31,43.05
3-Apr-12,629.32,46.03
2-Apr-12,618.63,51.03
30-Mar-12,599.55,53.42
29-Mar-12,609.86,57.82
28-Mar-12,617.62,59.01
27-Mar-12,614.48,56.03
26-Mar-12,606.98,58.01

redame.md

This is a follow on from the [dual line d3.js graph](http://bl.ocks.org/d3noob/8603837) used as an example in the book [D3 Tips and Tricks](https://leanpub.com/D3-Tips-and-Tricks).

It demonstrates the use of dual y axes to represent two different graph lines and should be taken in context with the text of the [book](https://leanpub.com/D3-Tips-and-Tricks) which can be downloaded for free from Leanpub.