title: Remove rows with same column value from DataTable and add corresponding values
body: <p>I have a DataTable with multiple columns. If the value of certain column repeats, I need to remove that row and add the quantities against it. For example, following datatable</p>
  
  <pre><code>ITEM    QTY
  ------------
  1       20
  2       10
  2       10
  3       20
  </code></pre>
  
  <p>would become:</p>
  
  <pre><code>ITEM    QTY
  -----------
  1       20
  2       20
  3       20
  </code></pre>
  
  <p>This is what I did </p>
  
  <pre><code>var table = dt.AsEnumerable() 
  .GroupBy(row =&gt; row.Field("ITEM")) 
  .Select(group =&gt; group.First()) 
  .CopyToDataTable();
  </code></pre>
  
  <p>It removes the extra row but doesn't add up the quantities. So please help me in this regard.</p>