Binaryworld - FilterDuplicates - Delete duplicate items in an array ... [ VB.net -> Arrays ]

' Filter out duplicate values in an array and compact
' the array by moving items to "fill the gaps".
' Returns the number of duplicate values
'
' The array is not REDIMed, but you can do it easily using
' the following code:
'   a() is a string array
'   dups = FilterDuplicates(a())
'   If dups Then
'     ReDim Preserve a(LBound(a) To UBound(a) - dups) As String
'   End If

Function FilterDuplicates(ByVal arr As Array) As Integer
  Dim index As Integer
  Dim dups As Integer
  ' we use a hashtable to track duplicates
  Dim ht As New Collections.Hashtable(arr.Length * 2)

  For index = 0 To arr.Length - 1
    Dim value As Object = arr.GetValue(index)

    If ht.Contains(value) Then
      ' we've found a duplicate
      arr.SetValue(Nothing, index)
      dups += 1
    Else
      ' add to the hashtable (use a dummy Nothing value)
      ht.Add(value, Nothing)
      ' if we've found one or more duplicates so far
      ' we need to move elements towards lower indices
      If dups > 0 Then
        arr.SetValue(value, index - dups)
        arr.SetValue(Nothing, index)
      End If
    End If
  Next

  ' return the number of duplicates
  Return dups

End Function