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rbecher
MVP
MVP

string matching with fuzzy, trigram (n-gram), levenshtein, etc.

Hi,

I'm looking for a possibility for string matching with fuzzy(-search), trigram (n-gram), levenshtein, etc. in QV script.

Any suggestions?

Ralf

Vizlib Head of R&D
26 Replies
rbecher
MVP
MVP
Author

We've made an implementation of Metaphone and Kölner Phonetik (special for German: http://de.wikipedia.org/wiki/K%C3%B6lner_Phonetik) in our profiling solution TIQView with QV script.

You can use regex with VB Macro but this is not very stable for large datasets loaded with script. We also tested this out a lot...

- Ralf

Vizlib Head of R&D
rbecher
MVP
MVP
Author

Another issue with VBScript regex is the limitation of regex operators! I hope for a plugable API to use Java or so in v10!

- Ralf

Vizlib Head of R&D
amien
Specialist
Specialist

Ralf,

are you talking about a function in the VBScript in QV? like the one i posted for Levenshtein_distance?

something like:

function Levenshtein_distance

....

End function

i assume that you are also doing some datacleaning during loading

rbecher
MVP
MVP
Author

If you're asking for a regex VBScript Function, here we go:

Function regExpMatch(ByVal strVal, ByVal strPattern)
Set objRegExpr = New RegExp
objRegRegExpr.Pattern = "^" & strPattern & "$"
objRegRegExpr.IgnoreCase = True
regExpMatch = objRegExpr.Test(strVal) * -1
End Function

- Ralf

Vizlib Head of R&D
amien
Specialist
Specialist

i have something like that..

but those function cant be used in an expression right? only in load script?

rbecher
MVP
MVP
Author

..as far as I know, yes.

- Ralf

Vizlib Head of R&D
Not applicable

Levenshtein Distance :

sub LevenshteinDistance(S1,S2)

    let lns1 = len(S1);

    let lns2 = len(S2);

    for i=0 to $(lns1)

        let `d[$(i),0]` = $(i);

        // trace d[$(i),0] = $(d[$(i),0]);

    next

    for j=0 to $(lns2)

        let `d[0,$(j)]` = $(j);

        // trace d[0,$(j)] = $(d[0,$(j)]);

    next

    for j=1 to $(lns2)

        for i=1 to $(lns1)       

            let k = $(i)-1;

            let l = $(j)-1;   

            // trace k : $(k), trace l : $(l);   

            let z = mid(S1,$(i),1);

            let w = mid(S2,$(j),1);

            // Trace z = $(z) vs. w = $(w);

            if ('$(z)'='$(w)') then

                let `d[$(i),$(j)]` = $(d[$(k),$(l)]);

                // Trace `d[$(i),$(j)]` = $(d[$(i),$(j)]);

            else

                let v1 = $(d[$(k),$(j)]); // insertion

                let v2 = $(d[$(i),$(l)]); // deletion

                let v3 = $(d[$(k),$(l)]); // substitution

                let `d[$(i),$(j)]` = rangemin($(v1),$(v2),$(v3))+1;

                // Trace `d[$(i),$(j)]` = $(d[$(i),$(j)]);   

            end if               

        next

    next

    let retour = $(d[$(lns1),$(lns2)]);

    Trace - word 1 : $(S1);

    Trace - word 2 : $(S2);

    Trace --------> retour = $(retour) : $(ids1s2) %;

end sub

Not applicable

Hello,

Is it possible to see some code which implements the above?  I have this same requirement and its driving me crazy.  I have 2 files both with client names (they might be spelt differently e.g. Qlik ltd and Qlik Limited or Qliktech) and I need to present the end user with suggested matches.

Many thanks

rbecher
MVP
MVP
Author

Hi Karen,

I found a workable VBScript implementation as a function. This can be used during LOAD on record level. So you would need to join the source data first:

LOAD Script:

Levenshtein:

LOAD F1, F2, levenshtein(F1,F2) as distance;

LOAD * INLINE [

    F1, F2

    Qlik, Qlik ltd

    Qlik ltd, Qlik Limited

    Qlik Limited, QlikTech

    Qlik, Klik

];

Module:

' Source:

' http://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Levenshtein_distance#VBScript

Function levenshtein( a, b )

    Dim i,j,cost,d,min1,min2,min3

' Avoid calculations where there there are empty words

    If Len( a ) = 0 Then levenshtein = Len( b 😞 Exit Function

    If Len( b ) = 0 Then levenshtein = Len( a 😞 Exit Function

' Array initialization   

    ReDim d( Len( a ), Len( b ) )

    For i = 0 To Len( a 😞 d( i, 0 ) = i: Next

    For j = 0 To Len( b 😞 d( 0, j ) = j: Next

' Actual calculation

    For i = 1 To Len( a )

        For j = 1 To Len( b )

                        If Mid(a, i, 1) = Mid(b, j, 1) Then cost = 0 Else cost = 1 End If

            ' Since min() function is not a part of VBScript, we'll "emulate" it below

            min1 = ( d( i - 1, j ) + 1 )

            min2 = ( d( i, j - 1 ) + 1 )

            min3 = ( d( i - 1, j - 1 ) + cost )

            If min1 <= min2 And min1 <= min3 Then

                d( i, j ) = min1

            ElseIf min2 <= min1 And min2 <= min3 Then

                d( i, j ) = min2

            Else

                d( i, j ) = min3

            End If

        Next

    Next

    levenshtein = d( Len( a ), Len( b ) )

End Function

Hope this helps..

- Ralf

Vizlib Head of R&D

View solution in original post

Not applicable

Awesome, thanks Ralf!  I found the same code but happy to have this confirmed as a good solution by an expert.

You are so helpful.  Thanks again