How about
x <- lookupTable
x[!(x %in% matchSample)] <- NA
pmatch(matchSample,x)
Regards,
Moshe.
--- On Mon, 23/6/08, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> From: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
> Subject: [R] One-to-one matching?
> To: r-help@r-project.org
> Received: Monday, 23 June, 2008, 12:57 PM
> Hi folks,
>
> Can anyone suggest an efficient way to do "matching
> without
> replacement", or "one-to-one matching"?
> pmatch() doesn't quite provide
> what I need...
>
> For example,
>
> lookupTable <-
> c("a","b","c","d","e","f")
> matchSample <-
> c("a","a","b","d")
> ##Normal match() behaviour:
> match(matchSample,lookupTable)
> [1] 1 1 2 4
>
> My problem here is that both "a"s in matchSample
> are matched to the same
> "a" in the lookup table. I need the elements of
> the lookup table to be
> excluded from the table as they are matched, so that no
> match can be
> found for the second "a".
>
> Function pmatch() comes close to what I need:
>
> pmatch(matchSample,lookupTable)
> [1] 1 NA 2 4
>
> Yep! However, pmatch() incorporates partial matching,
> which I
> definitely don't want:
>
> lookupTable <-
> c("a","b","c","d","e","aaaaaaaaf")
>
> matchSample <-
> c("a","a","b","d")
> pmatch(matchSample,lookupTable)
> [1] 1 6 2 4
> ## i.e. the second "a", matches
> "aaaaaaaaf" - I don't want this.
>
> Of course, when identical items ARE duplicated in both
> sample and lookup
> table, I need the matching to reflect this:
>
> lookupTable <-
> c("a","a","c","d","e","f")
> matchSample <-
> c("a","a","c","d")
> ##Normal match() behaviour
> match(matchSample,lookupTable)
> [1] 1 1 3 4
>
> No good - pmatch() is better:
>
> lookupTable <-
> c("a","a","c","d","e","f")
> matchSample <-
> c("a","a","c","d")
> pmatch(matchSample,lookupTable)
> [1] 1 2 3 4
>
> ...but we still have the partial matching issue...
>
> ##And of course, as per the usual behaviour of match(),
> sample elements
> missing from the lookup table should return NA:
>
> matchSample <-
> c("a","frog","e","d")
> ; print(matchSample)
> match(matchSample,lookupTable)
>
> Is there a nifty way to get what I'm after without
> resorting to a for
> loop? (my code's already got too blasted many of
> those...)
>
> Thanks,
>
> Alec Zwart
> CMIS CSIRO
> [EMAIL PROTECTED]
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained,
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