Distinct in datatable

This is how to do a distinct in a datatable in Visual Basic. It is derived from http://support.microsoft.com/default.aspx?scid=kb;en-us;326176#1 and also look at this definition http://weblogs.asp.net/eporter/archive/2005/02/10/370548.aspx for multiple columns / fields.

Private

Function ColumnEqual(ByRef A As Object, ByRef B As Object) As Boolean

' Compares two values to see if they are equal. Also compares DBNULL.Value.
' Note: If your DataTable contains object fields, then you must extend this
' function to handle them in a meaningful way if you intend to group on them.

If IsDBNull(A) And IsDBNull(B) Then

Return True

End If

If IsDBNull(A) Or IsDBNull(B) Then

Return False

End If

If A = B Then

Return True

End If

End Function

Public Function SelectDistinct(ByVal TableName As String, ByRef SourceTable As DataTable, ByVal FieldName As String) As DataTable

Dim dt As New DataTable(TableName)

Dim dr As DataRow

dt.Columns.Add(FieldName, SourceTable.Columns(FieldName).DataType)

Dim LastValue As Object = DBNull.Value

For Each dr In SourceTable.Select("", FieldName)

If IsDBNull(LastValue) Or Not ColumnEqual(LastValue, dr(FieldName)) Then

LastValue = dr(FieldName)

dt.Rows.Add(LastValue)

End If

Next

Return dt

End Function