title: Get one element from d3js selection, by index
body: <p>I've created a set of d3js elements based on an array of 3 elements:</p>
  
  <pre><code>var data = [[0,0,2],[0,23,5],[2,12,5]];
  circleSet = svg.selectAll()
               .data(data)
               .enter().append('circle');
  </code></pre>
  
  <p>edit:</p>
  
  <p>How can I select the second element by index?</p>