Dim records = From row As DataGridViewRow In DataGridViewReport.Rows
        Dim results = records.GroupBy(Function(t) t.Cells("R_BarCode").Value.ToString).[Select](Function(t) New With {Key .BarCode = t.Key, Key .SumPrezzo = t.Sum(Function(x) Convert.ToDecimal(x.Cells("R_Prezzo").Value))})

        For Each result In results
            Console.WriteLine("{0} = {1}", result.BarCode, result.SumPrezzo)
        Next