R help - Aug 2008 - String search: Return "closest" match

Hi,

I have to match names where names can be recorded with errors or additions.
Now I am searching for a string search function which returns always the
"closest" match. E.g. searching for  "Washington" it should
return only Washington but not Washington, D.C. But it also could be that the
list contains only "Hamburg" but the record I am searching for is
"Hamburg OTM" and then we still want to find "Hamburg". Or
maybe the list contains "Hamburg" and "Hamberg" but we are
searching for "Hamburg" and thus only this should this one should be
returned.

agrep() returns all "close" matches but unfortunately does not return
the degree of closeness otherwise selection would be easy.
Is there such a function already implemented?

Thanks a million for your help,
  Werner


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> I have to match names where names can be recorded with errors or 
additions.
> Now I am searching for a string search function which returns always
> the "closest" match. E.g. searching for  "Washington"
it should
> return only Washington but not Washington, D.C. But it also could be
> that the list contains only "Hamburg" but the record I am
searching
> for is "Hamburg OTM" and then we still want to find
"Hamburg". Or
> maybe the list contains "Hamburg" and "Hamberg" but we
are searching
> for "Hamburg" and thus only this should this one should be
returned.
> 
> agrep() returns all "close" matches but unfortunately does not 
> return the degree of closeness otherwise selection would be easy.
> Is there such a function already implemented?
The Levenshtein distance is a common metric for determining how close two 
string are (in fact, agrep uses this).  There's a function to calculate it 
on the R wiki.
http://wiki.r-project.org/rwiki/doku.php?id=tips:data-strings:levenshtein

You can use this to find the closest string.  (If your set of cities is 
large, it may be quickest to use agrep to narrow the selection first, 
since the pure R implementation of levenshtein is likely to be slow.)

Regards,
Richie.

Mathematical Sciences Unit
HSL


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That works perfectly, great.

Thanks a lot for that Richard!
  Werner



----- Urspr?ngliche Mail ----
Von: "Richard.Cotton at hsl.gov.uk" <Richard.Cotton at
hsl.gov.uk>
An: Werner Wernersen <pensterfuzzer at yahoo.de>
CC: r-help at stat.math.ethz.ch; r-help-bounces at r-project.org
Gesendet: Dienstag, den 26. August 2008, 14:10:11 Uhr
Betreff: Re: [R] String search: Return "closest" match
> I have to match names where names can be recorded with errors or 
additions.
> Now I am searching for a string search function which returns always
> the "closest" match. E.g. searching for  "Washington"
it should
> return only Washington but not Washington, D.C. But it also could be
> that the list contains only "Hamburg" but the record I am
searching
> for is "Hamburg OTM" and then we still want to find
"Hamburg". Or
> maybe the list contains "Hamburg" and "Hamberg" but we
are searching
> for "Hamburg" and thus only this should this one should be
returned.
> 
> agrep() returns all "close" matches but unfortunately does not 
> return the degree of closeness otherwise selection would be easy.
> Is there such a function already implemented?
The Levenshtein distance is a common metric for determining how close two 
string are (in fact, agrep uses this).  There's a function to calculate it 
on the R wiki.
http://wiki.r-project.org/rwiki/doku.php?id=tips:data-strings:levenshtein

You can use this to find the closest string.  (If your set of cities is 
large, it may be quickest to use agrep to narrow the selection first, 
since the pure R implementation of levenshtein is likely to be slow.)

Regards,
Richie.

Mathematical Sciences Unit
HSL


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