title: Using fields in inherited bound data
body: <p>I am attempting to get my head around using bound data with d3.js. I'm following the <a href="https://github.com/mbostock/d3/wiki/Selections#wiki-data" rel="nofollow">documentation</a> and am now a little confused. </p>
  
  <p>I want to produce donut charts with radii that vary depending on the data. I am comfortable producing the arcs to make up a donut using an array, but am having a hard time working out how to pass along a size parameter with the data binding of the arc. For example, if the data bound to the parent of the arc is something like <code>{size: 20, cont: [1, 7]}</code>, how can I bind the first element of the array <em>as well</em> as the size element? I have a <a href="http://jsfiddle.net/W9dMx/1/" rel="nofollow">fiddle</a> attempting to show what I am talking about. In that example, the two donuts should be different sizes. I have commented out the kind of thing I suspect should be going on on line 14.</p>
  
  <p>I have tried variations on:</p>
  
  <pre><code>var arcs = donuts.selectAll(".arc")
             .data(function(d) { var temp = [];
                      temp.push(d.cont);
                      temp.push(d.size);
                      return temp; })
             .enter()
             .append("g")
             .attr("class", "arc");
  </code></pre>
  
  <p>But it is clearly not producing what I expect. </p>