[AccessD] "fuzzy logic" search

Stuart,

Could you comment the code for me?  I have no idea what the hamming distance
is trying to accomplish and don't wish to take a class to figure it out.
Just a 1 paragraph overview at te top and a couple of line comments thrown
in would be a great help.

Thanks,

John W. Colby
www.colbyconsulting.com

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com]On Behalf Of Stuart
McLachlan
Sent: Wednesday, October 22, 2003 8:01 AM
To: Access Developers discussion and problem solving
Subject: Re: [AccessD] "fuzzy logic" search


On 21 Oct 2003 at 22:58, MartyConnelly wrote:

> Why not use a weighted checksum like the ISBN number, it will also
> indicated the position of a single substitution error and I think the
> location of a single transposition error.
>

Too many potential false matches

Combining HammingDistance with a straight Checksum seems to work
quite well though. Here's what I've come up with to test for a single
miskey or a transposition error:

Function HammingDistance(BaseString As String, TestString As String) As Long
Dim lngHamCount As Long
Dim lngLen As Long
lngLen = Len(BaseString)
If Len(TestString) <> lngLen Then
    HammingDistance = -1
    Exit Function
Else
  For loopcount = 1 To lngLen
     If Mid$(BaseString, loopcount, 1) <> Mid$(TestString, loopcount, 1)
Then
        lngHamCount = lngHamCount + 1
     End If
  Next
End If
HammingDistance = lngHamCount
End Function

Function CheckSum(TestString) As Long
Dim lngCheck As Long
For loopcount = 1 To Len(BaseString)
   lngCheck = lngCheck + Asc(Mid$(TestString, loopcount, 1))
Next
End Function

Function PossibleMatch(BaseString As String, TestString As String) As
Boolean
Select Case HammingDistance(BaseString, TestString)
    Case 1 ' Miskey?
       PossibleMatch = True
    Case 2  'Possible transposition?
       If CheckSum(BaseString) = CheckSum(TestString) Then
           PossibleMatch = True
       End If
    Case Else
       PossibleMatch = False
End Select
End Function
--
Lexacorp Ltd
http://www.lexacorp.com.pg
Information Technology Consultancy, Software Development,System Support.



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