title: Count the number of rows of a CSV file, with d3.js
body: <p>Suppose I have this CSV file</p>
  
  <pre><code>Day,What
  2013-10-27,Apple
  2013-10-27,Cake
  2013-10-27,Apple
  2013-10-28,Apple
  2013-10-28,Apple
  2013-10-28,Blueberry
  2013-10-28,Orange
  </code></pre>
  
  <p>I would like to drawn with D3.js a time-series graph. All I need to do is to display the sum of the number of rows for each day. As an example, the 27 of November should have 3 as value, the 28th should have 4.</p>
  
  <p>Is there a way I can archive it? I've been trying to create a new dataset out of the CSV one with no positive results.</p>
  
  <pre><code>var dataset;
  
  d3.csv("data.csv", function(d) {
    return {
      Day: new Date(d.Day),
      What: d.What
    };
  }, 
  
  function(error, rows) {
      dataset = rows;
      // I SUPPOSE THE FUNCTION THAT GENERATE THE NEW DATASET SHOULD GO THERE     
  });
  </code></pre>