title: Kettle: How to get max date for each group of rows
body: <p>I'm reading an excel sheet using Kettle and this sheet has three fields: code, description and date.</p>
  
  <p><strong>Example</strong>: </p>
  
  <pre><code>1 - description A - 01/JAN/2013
  2 - description A - 15/JAN/2013
  3 - description A - 04/JAN/2013
  4 - description B - 02/JAN/2013
  5 - description B - 16/JAN/2013
  6 - description B - 11/JAN/2013
  </code></pre>
  
  <p>What I want is to put an additional field <em>Max date</em> for each row, where max date is the latest date on a group based on description, like this:</p>
  
  <p><strong>Example 2</strong></p>
  
  <pre><code>1 - description A - 01/JAN/2013 - 15/JAN/2013
  2 - description A - 15/JAN/2013 - 15/JAN/2013
  3 - description A - 04/JAN/2013 - 15/JAN/2013
  4 - description B - 02/JAN/2013 - 16/JAN/2013
  5 - description B - 16/JAN/2013 - 16/JAN/2013
  6 - description B - 11/JAN/2013 - 16/JAN/2013
  </code></pre>
  
  <p>The group of rows with <em>description A</em> has the latest date 15/JAN/2013 (because of row 2).
  The group of rows with <em>description B</em> has the latest date 16/JAN/2013 (because of row 5).</p>