title: Group by and sum query on datatable
body: <p>I have a strongly typed <code>DataTable</code> that looks as follows:</p>
  
  <pre><code>|Team|FirstName|LastName|Hours
  |A|Henry|Manny|3
  |A|Henry|Manny|5
  |A|Johny|Tenny|2
  |A|Johny|Tenny|3
  |B|Frank|Tank|4
  |B|Frank|Tank|5
  </code></pre>
  
  <p>What I am trying to achieve is to sum the Hours by First and Lastname so my result table should look like:</p>
  
  <pre><code>|Team|FirstName|LastName|Hours
  |A|Henry|Manny|8
  |A|Johny|Tenny|5
  |B|Frank|Tank|9
  </code></pre>
  
  <p>I tried so many thinks. One of it was:</p>
  
  <pre><code>dim query = From row In _dataset.Table1.AsEnumerable
  Group by row.FirstName, row.LastName Into MAGroup = Group
  Select New with { . First = row.FirstName, .Last = row.LastName, .Sum = sum(MAGroup.Hours)}
  </code></pre>
  
  <p>But always as soon as I start with the first anonymous member in the Select statement I don't get intellisense help and everything is underlined. I really would be so thankful if anyone could help me with the query.</p>