title: How to group datatable by unknown column names and calculate sum of one field?
body: <p>I have a table like this:</p>
  
  <pre><code> Name    Age  Gender  
   Sasha   12      W  
   Sasha   20      W  
   Sasha   21      M  
   Bob     21      M
  </code></pre>
  
  <p>And I want to group by multiple fields, for example <code>[Name]</code> and <code>[Gender]</code> and sum this by field <code>[Age]</code>. The columns are unknown at compile time because the user can select them.</p>
  
  <p>So, in in this example i want this:</p>
  
  <pre><code> Name    Age  Gender  
   Sasha   32      W  
   Sasha   21      M  
   Bob     21      M
  </code></pre>
  
  <p>But I can't do it by LINQ, because I don't know the  columns at compile time.</p>
  
  <p>Thanks for answers!</p>