title: Access to previous row in Kettle
body: <p>In Pentaho ETL Kettle i would like to acces previous row in one step. 
  Let's declare data flow as myMat:</p>
  
  <p>myMat:</p>
  
  <pre><code>      col0  col1
  row0: 15    a
  row1: 10    b
  row2: 24    hi
  row3: 11    bye
  </code></pre>
  
  <p>I would like to use this calculation:</p>
  
  <pre><code>newNumber= myMat[i][0] + myMat[i-1][0]
  </code></pre>
  
  <p>Do you know any way to do it in Kettle? </p>