title: DataTable need to sum a column with filter on it
body: <p>I have a data table in C# with columns:</p>
  
  <blockquote>
    <p>Product|Status|ShipedVolume|TotalVolume</p>
  </blockquote>
  
  <pre><code>A     New        0           10     
  A     New        5           20
  B     Closed     7           20
  </code></pre>
  
  <p>I want to sum (TotalVolume-ShipedVolume) filtered by product and Status.</p>
  
  <p>For example I want to query how many not shipped item I have for product A, in this example the answer is 25.
  The same question for product B will be 0.</p>
  
  <p>How can I code it?</p>