title: d3 - sunburst - transition given updated data -- trying to animate, not snap
body: <p>I am working on a sunburst viz based off of Mike Bostock's <a href="http://bl.ocks.org/mbostock/4348373" rel="noreferrer">Zoomable Sunburst</a> example.</p>
  
  <p>I want to be able to change the underlying data using a whole new JSON (which has the same structure but different 'size' values), and have the sunburst animate a transition to reflect the updated data. </p>
  
  <p>If I change the data of the path elements using .data(), and then attempt to update in the following fashion:</p>
  
  <pre><code>path.data(partition.nodes(transformed_json))
      .transition()
      .duration(750)
      .attrTween("d", arcTween(transformed_json));
  </code></pre>
  
  <p>(..which is pretty much the exact same code as the click fn)</p>
  
  <pre><code>function click(d) {
     path.transition()
         .duration(750)
         .attrTween("d", arcTween(d));
  }
  </code></pre>
  
  <p>..I find that the sunburst does correctly change to reflect the new data, but it snaps into place rather than smoothly transitioning, like it does when you zoom in.</p>
  
  <p><a href="http://jsfiddle.net/jTV2y/" rel="noreferrer">http://jsfiddle.net/jTV2y/</a> &lt;-- Here is a jsfiddle with the issue isolated (the transition happens one second after you click 'Run')</p>
  
  <p>I'm guessing that I need to create a different arcTween() fn, but my d3 understanding is not there yet. Many thanks!</p>