[R] list matching

[Gabor Grothendieck]

zoo's merge can do a multiway intersection.  We turn each component
of aa into the times of a dataless zoo object (assuming the elements of
each component are unique) and merge them together using all = FALSE
which will only leave those points at times in all components.  Extracting
the time and stripping off the names gives the result.

library(zoo)
as.vector(time(do.call(merge, c(lapply(aa, function(x) zoo(,x)), all = FALSE))))


On 10/6/07, Adrian Dusa <dusa.adrian at gmail.com> wrote:
>
> Dear list,
>
> Given a list of elements like:
> aa <- list(one=c("o", "n", "e"),
>               tea=c("t", "e", "a"),
>               thre=c("t", "h", "r", "e"))
>
> Is there a function that returns the intersection between all?
> Both match() and intersect() only deal with two arguments, but sometimes I
> have more.
>
> Here, it should return "e" (or NA if none of the letters are common).
>
> I have a solution to apply %in% multiple times (here two times, first between
> the first two and then between the result and the third) but... perhaps there
> is a better and quicker way.
>
> Thanks in advance,
> Adrian
>
> --
> Adrian Dusa
> Romanian Social Data Archive
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> Romania
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