R help - Aug 2003 - index all subsets of k of m items?

How can I efficiently index all choose(m, k) subsets of m items taken 
k at a time?  For example, with (m, k) = (3, 2), the subsets are (1, 2), 
(1, 3), and (2, 3).  I'd like a function something like 
"index.subsets(subset, k, m)" that would return 1, 2 or 3 for these 3 
subsets.  Examples:

index.subsets(c(1,2), 2, 3) -> 1
index.subsets(c(1,3), 2, 3) -> 2
index.subsets(c(2,3), 2, 3) -> 3

index.subsets(c(1,2,3), 3, 5) -> 1
index.subsets(c(1,2,5), 3, 5) -> 3
index.subsets(c(3,4,5), 3, 5) -> 10

	  Thanks.
Spencer Graves

help.search("subset") on my R installation gives:

nchoosek(vsn)            List all subsets of size k from n objects

and "vsn" is one of the Bioconductor packages.  From that, the
index.subsets() you want shouldn't be too hard to construct...

HTH,
Andy
> -----Original Message-----
> From: Spencer Graves [mailto:spencer.graves at pdf.com] 
> Sent: Friday, August 01, 2003 6:56 AM
> To: R-help
> Subject: [R] index all subsets of k of m items?
> 
> 
> 	  How can I efficiently index all choose(m, k) subsets 
> of m items taken 
> k at a time?  For example, with (m, k) = (3, 2), the subsets 
> are (1, 2), 
> (1, 3), and (2, 3).  I'd like a function something like 
> "index.subsets(subset, k, m)" that would return 1, 2 or 3 for
these 3
> subsets.  Examples:
> 
> index.subsets(c(1,2), 2, 3) -> 1
> index.subsets(c(1,3), 2, 3) -> 2
> index.subsets(c(2,3), 2, 3) -> 3
> 
> index.subsets(c(1,2,3), 3, 5) -> 1
> index.subsets(c(1,2,5), 3, 5) -> 3
> index.subsets(c(3,4,5), 3, 5) -> 10
> 
> 	  Thanks.
> Spencer Graves
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list 
> https://www.stat.math.ethz.ch/mailman/listinfo> /r-help
> 
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