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Line Graph with Dual-scaled Axes using SVG and d3.js
<html>
<head>
<title>Line Graph with Dual-scaled Axes using SVG and d3.js</title>
<script src="http://mbostock.github.com/d3/d3.v2.js"></script>
<style>
/* tell the SVG path to be a thin blue line without any area fill */
path {
stroke-width: 1;
fill: none;
}
.data1 {
stroke: steelblue;
}
.data2 {
stroke: orange;
}
.axis {
shape-rendering: crispEdges;
}
.x.axis line {
stroke: lightgrey;
}
.x.axis .minor {
stroke-opacity: .5;
}
.x.axis path {
display: none;
}
.x.axis text {
font-size: 14;
}
.y.axis line, .y.axis path {
fill: none;
stroke: #000;
}
.y.axis text {
font-size: 14;
}
.y.axisRight text {
fill: orange;
}
.y.axisLeft text {
fill: steelblue;
}
</style>
</head>
<body>
<div id="graph" class="aGraph" style="position:absolute;top:0px;left:0; float:left;"></div>
<script>
/* implementation heavily influenced by http://bl.ocks.org/1166403 */
/* some arguments AGAINST the use of dual-scaled axes line graphs can be found at http://www.perceptualedge.com/articles/visual_business_intelligence/dual-scaled_axes.pdf */
// define dimensions of graph
var m = [80, 80, 80, 80]; // margins
var w = 900 - m[1] - m[3]; // width
var h = 400 - m[0] - m[2]; // height
// create a simple data array that we'll plot with a line (this array represents only the Y values, X will just be the index location)
var data1 = [3, 6, 2, 7, 5, 2, 0, 3, 8, 9, 2, 5, 9, 3, 6, 3, 6, 2, 7, 5, 2, 1, 3, 8, 9, 2, 5, 9, 2, 7];
var data2 = [543, 367, 215, 56, 65, 62, 87, 156, 287, 398, 523, 685, 652, 674, 639, 619, 589, 558, 605, 574, 564, 496, 525, 476, 432, 458, 421, 387, 375, 368];
// X scale will fit all values from data[] within pixels 0-w
var x = d3.scale.linear().domain([0, data1.length]).range([0, w]);
// Y scale will fit values from 0-10 within pixels h-0 (Note the inverted domain for the y-scale: bigger is up!)
var y1 = d3.scale.linear().domain([0, 10]).range([h, 0]); // in real world the domain would be dynamically calculated from the data
var y2 = d3.scale.linear().domain([0, 700]).range([h, 0]); // in real world the domain would be dynamically calculated from the data
// automatically determining max range can work something like this
// var y = d3.scale.linear().domain([0, d3.max(data)]).range([h, 0]);
// create a line function that can convert data[] into x and y points
var line1 = d3.svg.line()
// assign the X function to plot our line as we wish
.x(function(d,i) {
// verbose logging to show what's actually being done
console.log('Plotting X1 value for data point: ' + d + ' using index: ' + i + ' to be at: ' + x(i) + ' using our xScale.');
// return the X coordinate where we want to plot this datapoint
return x(i);
})
.y(function(d) {
// verbose logging to show what's actually being done
console.log('Plotting Y1 value for data point: ' + d + ' to be at: ' + y1(d) + " using our y1Scale.");
// return the Y coordinate where we want to plot this datapoint
return y1(d);
})
// create a line function that can convert data[] into x and y points
var line2 = d3.svg.line()
// assign the X function to plot our line as we wish
.x(function(d,i) {
// verbose logging to show what's actually being done
console.log('Plotting X2 value for data point: ' + d + ' using index: ' + i + ' to be at: ' + x(i) + ' using our xScale.');
// return the X coordinate where we want to plot this datapoint
return x(i);
})
.y(function(d) {
// verbose logging to show what's actually being done
console.log('Plotting Y2 value for data point: ' + d + ' to be at: ' + y2(d) + " using our y2Scale.");
// return the Y coordinate where we want to plot this datapoint
return y2(d);
})
// Add an SVG element with the desired dimensions and margin.
var graph = d3.select("#graph").append("svg:svg")
.attr("width", w + m[1] + m[3])
.attr("height", h + m[0] + m[2])
.append("svg:g")
.attr("transform", "translate(" + m[3] + "," + m[0] + ")");
// create yAxis
var xAxis = d3.svg.axis().scale(x).tickSize(-h).tickSubdivide(true);
// Add the x-axis.
graph.append("svg:g")
.attr("class", "x axis")
.attr("transform", "translate(0," + h + ")")
.call(xAxis);
// create left yAxis
var yAxisLeft = d3.svg.axis().scale(y1).ticks(4).orient("left");
// Add the y-axis to the left
graph.append("svg:g")
.attr("class", "y axis axisLeft")
.attr("transform", "translate(-15,0)")
.call(yAxisLeft);
// create right yAxis
var yAxisRight = d3.svg.axis().scale(y2).ticks(6).orient("right");
// Add the y-axis to the right
graph.append("svg:g")
.attr("class", "y axis axisRight")
.attr("transform", "translate(" + (w+15) + ",0)")
.call(yAxisRight);
// add lines
// do this AFTER the axes above so that the line is above the tick-lines
graph.append("svg:path").attr("d", line1(data1)).attr("class", "data1");
graph.append("svg:path").attr("d", line2(data2)).attr("class", "data2");
</script>
</body>
</html>
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