Re: [R] One-to-one matching?

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Sun, 22 Jun 2008 23:22:03 -0400

Try this. apseq() sorts the input and appends a sequence number: 0, 1, ... to successive occurrences of each value. Apply that to both vectors transforms it into a problem that works with ordinary match:

> lookupTable <- c("a", "a","b","c","d","e","f")
> matchSample <- c("a", "a","a","b","d")
>
> # sort and append sequence no
> apseq <- function(x) {

+ x <- sort(x)
+ s <- cumsum(!duplicated(x))
+ paste(x, seq(s) - match(s, s))
+ }

>
> match(apseq(matchSample), apseq(lookupTable))
[1] 1 2 NA 3 5

On Sun, Jun 22, 2008 at 10:57 PM, <Alec.Zwart_at_csiro.au> wrote:
> 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
> alec.zwart_at_csiro.au
>
> ______________________________________________
> R-help_at_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, reproducible code.
>



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon 23 Jun 2008 - 03:29:27 GMT

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