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Finding the last item in a collection

Posted on 2003-11-07
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Last Modified: 2010-05-03
I have a collection call colCustomers with a key element CustomerID.  CustomerID is in the sequence 0001, 0002, 0003 etc... However sometimes a key may be skipped eg: 0001, 0002, 0004, 0005, 0006.  I need to be able to find out what the last CustomerID is so that I can create a new one that is one number higher.  I don't want to create in a missing spot and I don't want to resort the collection and change every CustomerID so non are skipped.

Thanks, Jebus
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Question by:dj__jebus
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4 Comments
 
LVL 18

Expert Comment

by:Sethi
ID: 9705768
Count the no. of items in the collection. The total count -1 would be the last item. example:

Collection.Item(Collection.Count-1)
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Author Comment

by:dj__jebus
ID: 9705795
Well I have

NewCustomerID = colCustomers.Item(colCustomers.Count - 1).CustomerID + 1

and I get "This key is already asociated with an element of this collection" error.  I have tried this already and I think it does it because when a CustomerID is skipped the count is actually less than the highest CustomerID

Thanks, Jebus
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LVL 86

Expert Comment

by:Mike Tomlinson
ID: 9706012
Why not just store the last used CustomerID externally in a variable and increment it?
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LVL 86

Accepted Solution

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Mike Tomlinson earned 375 total points
ID: 9706035
This is the major drawback of a collection...it takes a long time to find the last item since it has to walk the linked list item by item.  Also there is no way to do a reverse key lookup given an index.

An alternative scheme would be to store the last used customerID in the first spot in the collection!  The objects in a collection do not have to be of the same data type and it would not be hard to modify existing code to not use the first index.
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