Comments on: Least Common Pathinator

By: Jan Chan

Jan Chan — Tue, 05 Sep 2006 10:54:00 +0000

Zach if you are having trouble getting to grips with recursion try to read this simple example.
Its a bit heavy on the annotation but I guess that helps.
I am not entirely happy with it, as it could do with a proper termination flag but I didn't want to make it too complicated to understand. I have tried to keep it as close to the examples above so the format is easier to pickup.

Just think about it as retracing your steps, and leaving behind some of the baggage you came with.

Function PathFinder(Path1, Path2, Optional PathDelimit As String = "") As String Dim strResult As String If Left(Path1, 1) = Left(Path2, 1) And (Path1 "" Or Path2 "") Then ' The string looks the same so far... ' go to the next character strResult = PathFinder(Mid(Path1, 2), Mid(Path2, 2), PathDelimit) If strResult = "" Then ' The end of the road no futher matches found..... If Left(Path1, 1) = PathDelimit Then ' We have found the end of the matches and we retraced our way back to the delimiter ' stick the delimiter on to the results ' Basically anything would have done here but I must not return an empty string. PathFinder = PathDelimit ' note path1 = path2 Else ' We have found the end of the matches but we haven't retraced our way back to a delimiter PathFinder = "" End If Else ' Everything is matching now lets just keep adding characters one at a time back to the results. PathFinder = Left(Path1, 1) & strResult End If Else ' We have found the end of the road this is the first proper difference. PathFinder = "" End IfEnd Function

By: Jan Chan

Jan Chan — Tue, 05 Sep 2006 10:26:00 +0000

Just think about it as retracing your steps, and leaving behind some of the baggage you came with.

Function PathFinder(Path1, Path2, Optional PathDelimit As String = "") As String
Dim strResult As String

If Left(Path1, 1) = Left(Path2, 1) And (Path1 "" Or Path2 "") Then
' The string looks the same so far...
' go to the next character
strResult = PathFinder(Mid(Path1, 2), Mid(Path2, 2), PathDelimit)
If strResult = "" Then
' The end of the road no futher matches found.....
If Left(Path1, 1) = PathDelimit Then
' We have found the end of the matches and we retraced our way back to the delimiter
' stick the delimiter on to the results
' Basically anything would have done here but I must not return an empty string.
PathFinder = PathDelimit ' note path1 = path2
Else
' We have found the end of the matches but we haven't retraced our way back to a delimiter
PathFinder = ""
End If
Else
' Everything is matching now lets just keep adding characters one at a time back to the results.
PathFinder = Left(Path1, 1) & strResult
End If
Else
' We have found the end of the road this is the first proper difference.
PathFinder = ""
End If
End Function

By: Andy Pope

Andy Pope — Sat, 26 Aug 2006 10:30:00 +0000

Thanks Jake.

By: Jake Marx

Jake Marx — Fri, 25 Aug 2006 21:19:00 +0000

Andy – I fixed your comment for you. You need to use vb and not vba in the tag.

Regards,
Jake

By: Zach

Zach — Fri, 25 Aug 2006 13:09:00 +0000

Thanks, Tushar. I did not get through it yet, but it looks like it will do the trick.

By: Andy Pope

Andy Pope — Fri, 25 Aug 2006 10:09:00 +0000

Doh! I see I used the markup tags from my usual forum rather those that work here.

By: Andy Pope

Andy Pope — Fri, 25 Aug 2006 08:36:00 +0000

Good catch Tushar.

Just in case my code caused any confusion regarding recursion, which it does NOT use, I have used a variable to hold the path whilst it is being built.

Function CommonPath2(Path1 As String, Path2 As String, Optional PathDelimit As String = "") As String

Dim vntP1 As Variant
Dim vntP2 As Variant
Dim lngIndex As Long
Dim strBuildPath As String

vntP1 = Split(Path1, PathDelimit)
vntP2 = Split(Path2, PathDelimit)

For lngIndex = LBound(vntP1) To WorksheetFunction.Min(UBound(vntP1), UBound(vntP2))
If StrComp(vntP1(lngIndex), vntP2(lngIndex), vbTextCompare) 0 Then Exit For
strBuildPath = strBuildPath & vntP1(lngIndex) & PathDelimit
Next
CommonPath2 = strBuildPath

End Function

By: Tushar Mehta

Tushar Mehta — Fri, 25 Aug 2006 02:21:00 +0000

Interesting capability. I wonder where this would be useful.

Some technical comments:

Dick: Untested: The For I= loop should go to Min(Len(Path1),Len(Path2))

Andy: Also untested: The loop should go to Min(Ubound(vntP1),Ubound(vntP2))

Zach: Since you asked so nicely {grin}, I expedited a planned reorganization of one section of my website. See
Recursion
http://www.tushar-mehta.com/publish_train/book_vba/07_recursion.htm

By: zach

zach — Fri, 25 Aug 2006 00:23:00 +0000

Aargh. I will bow to the feet of the first person who can explain recursion to me. I get the concept, it's just that I get lost when I try to compile the code in my head and keep track of what happens when the function calls itself.

It looks so simple and elegant, though.

By: Alex J

Alex J — Thu, 24 Aug 2006 19:58:00 +0000

I like Andy's approach.

I was going to suggest breaking down the first path (Split would do nicely), and then compare using something like:

If Path2 Like Path1 & "*"

rebuilding the Path1 from its components until the match either breaks or is complete.