How to add unique items in a collection

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Posted on September 6, 2010

There are instances where you will be having sevaral items and you only need to add unique items into a collection. Here is one of the way I can think of in VB6:

Instructions:

Create a new Project
Add a new module to it and name it as module1

Let's say you have sevaral items as shown below to a collection col:

John
Joseph
Jawahar
Rahim
Rahul
Raghu
Rao
Joseph
Rahim
John
Andrew
Steve
Jawahar

As you can see some of the items are duplicates. We only want to add unique items to the collection.

Copy the following code to module1:

Option Explicit
 
Private Sub Main()
  Dim col As New Collection
  Dim sItem As String
  Dim oVar As Variant
 
  Call AddUniqueItemsToCollection(col, "John")
  Call AddUniqueItemsToCollection(col, "Joseph")
  Call AddUniqueItemsToCollection(col, "Jawahar")
  Call AddUniqueItemsToCollection(col, "Rahim")
  Call AddUniqueItemsToCollection(col, "Rahul")
  Call AddUniqueItemsToCollection(col, "Raghu")
  Call AddUniqueItemsToCollection(col, "Rao")
  Call AddUniqueItemsToCollection(col, "Joseph")
  Call AddUniqueItemsToCollection(col, "Rahim")
  Call AddUniqueItemsToCollection(col, "John")
  Call AddUniqueItemsToCollection(col, "Andrew")
  Call AddUniqueItemsToCollection(col, "Steve")
  Call AddUniqueItemsToCollection(col, "Jawahar")
 
  For Each oVar In col
    Debug.Print oVar
  Next oVar
 
  'As you can see all duplicate items are removed from the colection
End Sub
 
Private Sub AddUniqueItemsToCollection(ByRef col As Collection, ByVal sItem As String)
    On Error GoTo AddUniqueItemsToCollection_Error
 
    col.Add sItem, sItem
 
    On Error GoTo 0
    Exit Sub
 
AddUniqueItemsToCollection_Error:
    If Err.Number = 457 Then
        'the item already exist
        Exit Sub
    Else
        MsgBox "Error " & Err.Number & " (" & Err.Description & ") in procedure AddUniqueItemsToCollection of Module Module1"
    End If
End Sub