Dim dt As New DataTable
 
dt.Columns.Add("Datum", GetType(Date))
dt.Columns.Add("Signal", GetType(Integer))
dt.Columns.Add("Dauer", GetType(Integer))
 
'Beispieldaten
For i As Integer = 1 To 10
   dt.Rows.Add(CDate("1.1.2015"), 1, 40)
   dt.Rows.Add(CDate("1.1.2015"), 2, 100)
   dt.Rows.Add(CDate("2.1.2015"), 1, 500)
   dt.Rows.Add(CDate("2.1.2015"), 2, 1000)
Next i
 
Dim q = From x As DataRow In dt.AsEnumerable _
            Let Datum = x("Datum")
            Let Signal = x("Signal")
            Let Dauer As Decimal = CDec(x("Dauer"))
        Group Dauer By Datum, Signal Into Sum(Dauer)