Imports System.Linq

Module Module1

    Sub Main()

        Dim testData As New List(Of Tuple(Of String, Integer))

        testData.Add(Tuple.Create("r1", 5))
        testData.Add(Tuple.Create("r1", 15))
        testData.Add(Tuple.Create("r2", 15))
        testData.Add(Tuple.Create("r2", 20))
        testData.Add(Tuple.Create("r2", 5))
        testData.Add(Tuple.Create("r2", 35))

        Dim result = testData.GroupBy(Function(t) t.Item1).Select(Function(t) New With {Key .Item1 = t.Key, Key .Sum = t.Sum(Function(x) x.Item2)})

        For Each t In result
            Console.WriteLine("{0} = {1}", t.Item1, t.Sum)
        Next

        Console.ReadLine()

    End Sub

End Module