title: No overload for method 'select' takes 2 arguments
body: <p>i'm trying to get two values from my query but i get this error:</p>
  
  <p>"No overload for method 'select' takes 2 arguments"</p>
  
  <p>Here is my code:</p>
  
  <pre><code>    public class myType
      {
          public long anId{ get; set; }
          public float aCost{ get; set; }
      }
  
      IEnumerable&lt;myType&gt; result = myDataTable.AsEnumerable().GroupBy(p =&gt; p["Id"]).Select(a =&gt; a["Id"], t =&gt; t.Sum(p =&gt; p["Cost"].ToFloat()));
  </code></pre>
  
  <p>How can i do that?</p>