Hi Tony -- off-list, as I think you're looking for something else...
"Tony Chiang" <[EMAIL PROTECTED]> writes:
> Hi all,
>
> I don't know if this is the correct venue for this question, but I am sure
> that someone will correct me if I am in the wrong list.
>
> I have been searching throughout R for a function that can find the
> intersection of multiple sets of "things". Say for instance, I have a list
> of $n$ character vectors and would like to find the intersection of all $k$
> subsets. I don't believe that there is such a function to do this (or am I
> wrong?). It is a pretty easy to encode such a function...there was an e-mail
> about how a recursive function to intersect an arbitrary number of sets
> which is elegant and useful (sorry I forgot the person's name who wrote the
> 2 line function).
Maybe this is what you were thinking of?
Intersect=function(x, ...) {
if (length(list(...))>1)
Intersect(x, Intersect(...))
else
intersect(x, ...)
}
> Intersect(letters[1:5], letters[3:6], letters[4:7])
[1] "d" "e"
> l=list(letters[1:5], letters[3:6], letters[4:7])
> do.call("Intersect", l)
[1] "d" "e"
Also
> Reduce(intersect, l, letters)
[1] "d" "e"
This won't be efficient for a large set of 'things', and I'm not
getting how n and k fit in -- 'all k subsets' implies all elements of
n?
Martin
> My question is two-fold:
>
> 1. If such a function already exists, what is it called?
> 2. If such a function does not exists, it is worthwhile to encode it (i.e.
> can I send my code to someone?).
>
> Cheers,
> --tony
>
> [[alternative HTML version deleted]]
>
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--
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109
Location: Arnold Building M2 B169
Phone: (206) 667-2793
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