Dim results = DataGridViewReport.Rows.GroupBy(Function(t) t.Cells("R_BarCode").Value.ToString).[Select](Function(t) New With { _
    Key.BarCode = t.Key, _
    Key.SumQualcosa = t.Sum(Function(x) x.Cells("AltraColonnaDaSommare").Value) _
  })
  
  For Each result In results
    Console.WriteLine("{0} = {1}", result.BarCode, result.SumQualcosa)
  Next