Dim records = New List(Of Tuple(Of String, Integer))() From {   Tuple.Create("r1", 10),Tuple.Create("r1", 5),Tuple.Create("r2", 7),Tuple.Create("r2", 3),Tuple.Create("r2", 5), Tuple.Create("r3", 6), Tuple.Create("r3", 6),Tuple.Create("r3", 6)}

Dim results = records.GroupBy(Function(t) t.Item1).[Select](Function(t) New With {Key .Item1 = t.Key,Key .SumItem2 = t.Sum(Function(x) x.Item2) })

For Each result As var In results
  Console.WriteLine("{0} = {1}", result.Item1, result.SumItem2)
Next