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@d3noob
Last active November 30, 2019 18:33
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Colour gradient on a graph line
license: mit

This is a follow on from the simple d3.js graph used as an example in the book D3 Tips and Tricks.

It is aimed at demonstrating the application of a colour gradient to the line of a line graph using d3.js. It should be taken in context with the text of the book which can be downloaded for free from Leanpub.

date close
1-May-12 58.13
30-Apr-12 53.98
27-Apr-12 67.00
26-Apr-12 89.70
25-Apr-12 99.00
24-Apr-12 130.28
23-Apr-12 166.70
20-Apr-12 234.98
19-Apr-12 345.44
18-Apr-12 443.34
17-Apr-12 543.70
16-Apr-12 580.13
13-Apr-12 605.23
12-Apr-12 622.77
11-Apr-12 626.20
10-Apr-12 628.44
9-Apr-12 636.23
5-Apr-12 633.68
4-Apr-12 624.31
3-Apr-12 629.32
2-Apr-12 618.63
30-Mar-12 599.55
29-Mar-12 609.86
28-Mar-12 617.62
27-Mar-12 614.48
26-Mar-12 606.98
<!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;
}
.line {
fill: none;
stroke: url(#line-gradient);
stroke-width: 2px;
}
</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: 30, left: 50},
width = 600 - margin.left - margin.right,
height = 270 - margin.top - margin.bottom;
// Parse the date / time
var parseDate = d3.time.format("%d-%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 valueline = d3.svg.line()
.x(function(d) { return x(d.date); })
.y(function(d) { return y(d.close); });
// 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("data.csv", function(error, data) {
data.forEach(function(d) {
d.date = parseDate(d.date);
d.close = +d.close;
});
// 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.close; })]);
svg.append("linearGradient")
.attr("id", "line-gradient")
.attr("gradientUnits", "userSpaceOnUse")
.attr("x1", 0).attr("y1", y(0))
.attr("x2", 0).attr("y2", y(1000))
.selectAll("stop")
.data([
{offset: "0%", color: "red"},
{offset: "40%", color: "red"},
{offset: "40%", color: "black"},
{offset: "62%", color: "black"},
{offset: "62%", color: "lawngreen"},
{offset: "100%", color: "lawngreen"}
])
.enter().append("stop")
.attr("offset", function(d) { return d.offset; })
.attr("stop-color", function(d) { return d.color; });
// Add the valueline path.
svg.append("path")
.attr("class", "line")
.attr("d", valueline(data));
// 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>
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