Question

Basically, I want my graph to start at the x-axis and grow over two seconds to the actual data values. This is probably a simple thing, but I can’t seem to get it to work.

I’m appending an area element, in which the d=”” attribute is built by a function (area) and I’m not sure where to add a transition.

First I thought to do this in the area function, but this fails. I’ve also tried to do this when the area element is added without success.

Here is my code:

// Create the area element for each object - a function that will be passed to "path"
var area = d3.svg.area()
    .x(function(d) { return x(d.year); })
    .y0(height)
    //.y1(height)
    //.transition()
    //.duration(2000)
    .y1(function(d) { return y(d.average); });

// build the container SVG element
var svg = d3.select("#co2").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 + ")")

svg.append("path") 
    // pull in data to the path 
    .datum(data)
    .attr("class", "area")
    // passing in the area function, for each object
    .attr("d", area)
    // starts the graph opacity at 0 and fades to 1 over 2.5 seconds
    .style("fill-opacity", "0")
    .transition()
    .duration(2500)
    .style("fill-opacity", "1");

Answer 1

Rather than try to use transition on the shape of the area graph, you could apply a scale(x,y) transform against the whole svg element that you want to animate. The advantage of this approach is that it is not limited to a particular rendering implementation (eg: not path/d3.area specific).

There are a couple of gotchas to note though:

• To avoid the transition() behaviour, working on the margin adjustments, make sure you have a separate ‘g’ element for the transition() transforms to act on

• SVG has its origin (0,0) in the top-left, so in addition to scaling the SVG area, you need to set the base of the graph

This is put together below:

‘g’ element:

var svg = d3.select("#co2").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 + ")")
    // define a new 'g' to scope the transition, and keep separate from the margin adjusting transform above
    .append("g"); 

transition() including base adjustment:

svg
  .attr("transform", "translate(0," + height + ") scale(1, 0)")
.transition().duration(2000)
  .attr("transform", "translate(0,0) scale(1, 1)");

As ever, this is best illustrated with the complete example: http://bl.ocks.org/4239516