D3 Multiline Chart

In the previous article we have talked about line charts. The example we worked on was a single line chart. We have worked with only single line . But there will be circumstances where we will be in need of draw chart with more than one set of data. So, what it will look like? Ofcourse, it will be a multiline chart. We are going to discuss about all the things that there are in multiline charts in this article.

This line chart is constructed from a TSV file storing the daily average temperatures of Kolkata, Delhi and Mumbai over the last month. The chart employs conventional margins and a number of D3 features.

Let us look through the visuals first, then we will see how to get the structure.

temp_line_chart

As you can see in the picture that we have temparature reading of three major cities of india in May 2014. the temparature readings are in celcius. With this chart we can easily determine the average temparature of the three cities during last month.

So, the question is how do we achive this? At first we will be in need of data. Which we have saved in a file named data.csv. Now let us look at the html coding.

HTML file:

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

body {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis path {
  display: none;
}

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

</style>
<body>
<script src="http://d3js.org/d3.v3.js"></script>
<script>

var margin = {top: 20, right: 80, bottom: 30, left: 50},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var parseDate = d3.time.format("%Y%m%d").parse;

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

var y = d3.scale.linear()
    .range([height, 0]);

var color = d3.scale.category10();

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

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

var line = d3.svg.line()
    .interpolate("basis")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.temperature); });

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 + ")");

d3.tsv("data.tsv", function(error, data) {
  color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));

  data.forEach(function(d) {
    d.date = parseDate(d.date);
  });

  var cities = color.domain().map(function(name) {
    return {
      name: name,
      values: data.map(function(d) {
        return {date: d.date, temperature: +d[name]};
      })
    };
  });

  x.domain(d3.extent(data, function(d) { return d.date; }));

  y.domain([
    d3.min(cities, function(c) { return d3.min(c.values, function(v) { return v.temperature; }); }),
    d3.max(cities, function(c) { return d3.max(c.values, function(v) { return v.temperature; }); })
  ]);

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

  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Temperature (ºc)");

  var city = svg.selectAll(".city")
      .data(cities)
    .enter().append("g")
      .attr("class", "city");

  city.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) { return color(d.name); });

  city.append("text")
      .datum(function(d) { return {name: d.name, value: d.values[d.values.length - 1]}; })
      .attr("transform", function(d) { return "translate(" + x(d.value.date) + "," + y(d.value.temperature) + ")"; })
      .attr("x", 3)
      .attr("dy", ".35em")
      .text(function(d) { return d.name; });
});
</script>
  </body>
</html>

Explanation of the code:

At first we need to set up the measuring points to draw the graph. To do it we have to do

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

  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Temperature (ºc)");

Next we have to get the data added to the system. For that we have to do

d3.tsv("data.tsv", function(error, data) {
  color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));

Regarding of the above example i can tell you that it is a basic example. You definetly can add more than the data we have give. And make a more complex multi line chart.

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