Function vRank2(ByVal dt As DataTable, _
                    ByVal rohwert_spalte As String, _
                    ByVal rangwert_spalte As String) As Boolean
 
        If dt Is Nothing Then Return False
        If dt.Rows.Count < 1 Then Return False
        If Not dt.Columns.Contains(rohwert_spalte) Then Return False
        If Not dt.Columns.Contains(rangwert_spalte) Then Return False
 
        Try
            Dim sortList As List(Of Decimal) = _
            (From row As DataRow In dt.AsEnumerable() _
             Order By row.Field(Of Decimal)(rohwert_spalte) _
             Select row.Field(Of Decimal)(rohwert_spalte)).ToList()
 
            Dim val As Decimal, index_ug, index_og As Integer
            For Each row As DataRow In dt.Rows
                val = row(rohwert_spalte)
                index_ug = sortList.IndexOf(val) + 1
                index_og = sortList.LastIndexOf(val) + 1
                row(rangwert_spalte) = meanrank(index_ug, index_og)
            Next row
            Return True
        Catch
            Return False
        End Try
    End Function
 
 
    Private Function meanrank(ByVal index_ug As Integer, _
                              ByVal index_og As Integer) As Decimal
        'Berechnung des mittleren Rangs in einem Bereich
        Dim mr As Decimal = 0
        For i As Integer = index_ug To index_og
            mr += i
        Next i
        Return mr / (index_og - index_ug + 1)
    End Function