Loop and Index Problem

[Hap]

I have a loop that is trying to remove duplicate values in a collection.

As in:

For Each iitem In newArea.theCollection
For q = 2 To newArea.theCollection.Count
If iitem.X = newArea.theCollection(q).X Then
If iitem.Y = newArea.theCollection(q).Y Then
newArea.theCollection.Remove(q)
End If
End If
Next q
Next iitem

The problem is that the For loop containing q as the increment apparently does not recheck the value of newArea.theCollection.Count at each increment. So I get an out of range error after an item has been removed.

Hopefully the dilemma is clear.

Any help would be appreciated.

 

[Greg Truby]

Loop backwards
for q = .Count to 2 step -1
(note implied use of WITH which would make object reference resolution quicker.)

 

[Hap]

Actually it appears that I am going to run into another problem with this loop. When the iitem index is the same as q then the values will always be the same and try to remove itself.

I am trying to compare the two individual property values of each iitem to every other iitem in the collection and remove only the duplicates.

There is an easy solution here somewhere.

 

[Hap]

I tried this:

For Each iitem In newArea.theCollection
For q = newArea.theCollection.Count To 1 Step -1
d = 0
If iitem.X = newArea.theCollection(q).X And iitem.Y = newArea.theCollection(q).Y Then
d = d + 1
End If
If d > 1 Then
newArea.theCollection.Remove (q)
End If
Next q
Next iitem


But this is not removing the duplication when checking the first two index values.

 

[Greg Truby]

for i = .count-1 to 1 step -1
    for j = .count to i+1 step -1
         compare / remove
    next j
next i

Would do it, I'd think (not tested). But I get a bad vibe from this code. Normally one of the key benefits of a collection is that it does not allow duplicates from the get-go. The very fact that you wound up with duplicates seems to indicate a greater problem to me...

 

[Hap]

Here is the solution:

For d = theCollection.Count To 2 Step -1
For q = d - 1 To 1 Step -1
If theCollection(d).X = theCollection(q).X And theCollection(d).Y = theCollection(q).Y Then
theCollection.Remove (d)
End If
Next q
Next d

Points are added to the collection from other collections and arrays. I could test for duplicates at that time but it seemed simpler to check only once after all the points were in.