javascript - d3 JSON multiple line chart

Question

I'm trying to make a plot with multiple lines on it from a JSON blob that looks like:

{"2007": [{"val":10, "mon":10}, {"val":20, "mon":11}, {"val":40, "mon":12}, ...],
 "2008": [{"val":20, "mon":8}, {"val":20, "mon":9}, {"val":40, "mon":10}, ...],
  ...
 "2012": [{"val":40, "mon":8}, {"val":50, "mon":9}, {"val":60, "mon":10}, ...]
}

The data is basically monthly totals for each year, with some years not having data for some months. I can't figure out exactly how to parse the data in d3 though. I tried various ways such as

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

svg.selectAll(".line")
 .data(series)
 .enter().append("path")
 .attr("class", "line")
 .attr("d", line);

But I can't seem to get the data into the SVG line. Any suggestions? Is there a better way to structure the JSON?

Answer 1

Here's what worked out in case anyone else runs across this problem. The trick is to pass a function that returns the values in the associative array in the "d" attribute of the path element.

  entries = d3.entries(data);

  var colors = d3.scale.category20()
    .domain(d3.keys(data));

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

  svg1.selectAll(".line")
    .data(entries)
  .enter().append("path")
    .attr("class", "line")
    // function(d), not just line function 
    .attr("d", function(d){ return  line(d.value); })
    .attr("stroke", function(d) { return colors(d.key) });

Some help from this answer too: Using nested data with javascript D3 problem