D3js - Creating and easily updating a multi-line chart

Question

I've created a little test line chart using D3, but since I am quite new to the library I am not sure what the best way would be to add multiple lines to a chart, at the moment I only have one line displayed in this fiddle.

I would like to display 2 lines on the chart, but I am unsure of how to achieve that without copy pasting code, which I am sure would be very inefficient as I would like to update/animate the graph at regular intervals based on user selection.

Instead of this,

var data = [12345,22345,32345,42345,52345,62345,72345,82345,92345,102345,112345,122345,132345,142345];

I would like to display something like this,

var data = [
            [12345,42345,3234,22345,72345,62345,32345,92345,52345,22345], // line one
            [1234,4234,3234,2234,7234,6234,3234,9234,5234,2234] // line two
          ];

Would this be a possibility? If so, what would be the best way to approach this, so that I can easily update/animate the graph when needed?

Note: I am merely trying to learn and to familiarize myself with D3 best practices and the library as a whole. Thanks.

Answer 1

This is possible and reasonable. There is a tutorial that approaches this at the D3 Nested Selection Tutorial which describes nesting of data.

Below is code that I hacked from your fiddle to demonstrate this.

var data = [        
[12345,42345,3234,22345,72345,62345,32345,92345,52345,22345], 
[1234,4234,3234,2234,7234,6234,3234,9234,5234,2234] 
          ];

var width = 625,
    height = 350;

var x = d3.scale.linear()
    .domain([0,data[0].length])   // Hack. Computing x-domain from 1st array
    .range([0, width]);

var y = d3.scale.linear()
    .domain([0,d3.max(data[0])])  // Hack. Computing y-domain from 1st array
    .range([height, 0]);

var line = d3.svg.line()
    .x(function(d,i) { return x(i); })
    .y(function(d) { return y(d); });

var area = d3.svg.area()
    .x(line.x())
    .y1(line.y())
    .y0(y(0));

var svg = d3.select("body").append("svg")
    //.datum(data)
    .attr("width", width)
    .attr("height", height)
  //.append("g");

var lines = svg.selectAll( "g" )
  .data( data );  // The data here is two arrays

// for each array, create a 'g' line container
var aLineContainer = lines
  .enter().append("g");  

/*svg.append("path")
    .attr("class", "area")
    .attr("d", area);*/

aLineContainer.append("path")
    .attr("class", "area")
    .attr("d", area);

/*svg.append("path")
    .attr("class", "line")
    .attr("d", line);*/

aLineContainer.append("path")
    .attr("class", "line")
    .attr("d", line);

/*svg.selectAll(".dot")
    .data(data)
  .enter().append("circle")
    .attr("class", "dot")
    .attr("cx", line.x())
    .attr("cy", line.y())
    .attr("r", 3.5);*/
// Access the nested data, which are values within the array here
aLineContainer.selectAll(".dot")
  .data( function( d, i ) { return d; } )  // This is the nested data call
  .enter()
    .append("circle")
    .attr("class", "dot")
    .attr("cx", line.x())
    .attr("cy", line.y())
    .attr("r", 3.5);
​

One deficiency is that I computed the domain for the x and y axes off the first array, which is a hack, but not pertinent to your question exactly.