Because I had to write a DistinctRows function last night, today I looked at the May bits of VS2005 to see if they had addressed this really obvious need, and indeed they did! Hooray hoorah!

OverLoads Public Function ToTable( _ ByVal distinct As Boolean, _ ByVal columnNames() As String _) As DataTable

Here’s the quick hack I wrote last night if you want to use it. It sorts the table on the keyfield then walks through it grabbing every row where the value of the key field changes and stuffing it into a new datatable that is returned. No rocket science. Just another one of those things I wonder why I had to write the code.

(note – the int32_key is in there as a reminder in case I need to create another one for non-int keys)

Public Function DistinctRows_Int32_Key(ByVal dt As DataTable, ByVal keyfield As String) As DataTable
  Dim newTable As DataTable = dt.Clone
  Dim keyval As Int32 = 0
  Dim dv As DataView = dt.DefaultView
  dv.Sort = keyfield
  If dt.Rows.Count > 0 Then
    For Each dr As DataRow In dt.Rows
      If Not dr.Item(keyfield) = keyval Then
        newTable.ImportRow(dr)
        keyval = dr.Item(keyfield)
      End If
    Next
  Else
    newTable = dt.Clone
  End If
  Return newTable
End Function