title: Linq query to sum by group
body: <p>I have a data table like this: </p>
  
  <pre><code>Category         Description       CurrentHours      CTDHours  
  LC1              Cat One                 5               0  
  LC2              Cat Two                 6               0  
  LC3              Cat Three              18               0  
  LC1              Cat One                 0               9  
  LC2              Cat Two                 0              15  
  LC4              Cat Four                0              21  
  </code></pre>
  
  <p>That I need to Group and Sum to this:  </p>
  
  <pre><code>Category         Description       CurrentHours      CTDHours  
  LC1              Cat One                 5              14  
  LC2              Cat Two                 6              21  
  LC3              Cat Three              18               0  
  LC4              Cat Four                0              21  
  </code></pre>
  
  <p>In other words I need to sum the two Hours columns grouping by the Category and Description columns.</p>
  
  <p>I know that I could build a new table and loop through the existing data and sum the data into the new table but I thought there would be an easier way to do it using Linq. I've googled it for a few hours but all the examples I found didn't seem to fit what I was trying to do.</p>
  
  <p>BTW, the odbc driver that creates the data table does not have the capability for sub queries, etc. or I would have just done it using SQL.</p>