title: d3.js Update circle on line chart
body: <p>I'm posting there because I couldn't find something on other post or on google.</p>
  
  <p><a href="http://jsfiddle.net/CUQaN/9/" rel="nofollow">http://jsfiddle.net/CUQaN/9/</a></p>
  
  <p>As you can see on the JS fiddle, I have a line chart with circle on each point.
  I want to update this chart with new data. The problem is that I can receive less or more point than I already have on the graph. For example, I can have 8 point on my line chart and then when I'm updating the chart, I can have just 4, or even 15 point. And my circle are not updating properly because I'm just changing the value of the circle which already exist.
  But I really don't know how to update them properly.</p>
  
  <p>I can have that data sometimes :</p>
  
  <pre><code>            var data = [
                  {"date":"4-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"3-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"2-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"1-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"30-Apr-12","close":Math.random()*354.98,"open":Math.random()*424.56},
                  {"date":"27-Apr-12","close":Math.random()*24.00,"open":Math.random()*253.89},
                  {"date":"26-Apr-12","close":Math.random()*490.70,"open":Math.random()*215.54},
                  {"date":"25-Apr-12","close":Math.random()*42.00,"open":Math.random()*351.23},
                  {"date":"24-Apr-12","close":Math.random()*210.28,"open":Math.random()*20.23},
                  {"date":"23-Apr-12","close":Math.random()*20.70,"open":Math.random()*368.34},
                  {"date":"20-Apr-12","close":Math.random()*412.98,"open":Math.random()*42},
                  {"date":"19-Apr-12","close":Math.random()*26.44,"open":Math.random()*20.56},
                  {"date":"18-Apr-12","close":Math.random()*48.34,"open":Math.random()*356.45},
                  {"date":"17-Apr-12","close":Math.random()*26.44,"open":Math.random()*20.56},
                  {"date":"15-Apr-12","close":Math.random()*48.34,"open":Math.random()*356.45},
              ];
  </code></pre>
  
  <p>And just that data other times : (more or less)</p>
  
  <pre><code>            var data = [
                  {"date":"4-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"3-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"2-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"1-May-12","close":Math.random()*568.13,"open":Math.random()*35.12},
                  {"date":"30-Apr-12","close":Math.random()*354.98,"open":Math.random()*424.56},
              ];
  </code></pre>
  
  <p>Is someone can help me please ?</p>
  
  <p>Thanks a lot !</p>