Try this one liner. The first argument of rep is the sorted intersection and the second argument is the calculated from the parallel minimum of the counts of elements in a that are also in b and the counts of elements in b that are also in a.
rep(sort(intersect(a, b)), pmin(table(a[a %in% b]), table(b[b %in% a]))) It does have the advantage of not introducing factors. On Thu, May 20, 2010 at 6:24 PM, Jonathan <jonsle...@gmail.com> wrote: > Thanks, but that doesn't quite work, since I'd want the result of b[b %in% > a] to be symmetric with a[a%in%b] (so if there are two 2's in EACH vector, > I'll get two 2's in the result, but if there are two 2's in only one vector, > but one two in the other, the result will show only one 2. > > Consider: > >> a <- c(2,4,3) >> b<-c(6,6,5,2,2,8,4) > >> b[b %in% a] > [1] 2 2 4 > >> a[a%in%b] > [1] 2 4 > > The second answer is correct, but I can't predict which variable to put in > which position in the statement, so I'd need them both to be correct. > > Best, > Jonathan > > On Thu, May 20, 2010 at 6:10 PM, David Winsemius > <dwinsem...@comcast.net>wrote: > >> >> On May 20, 2010, at 5:58 PM, Jonathan wrote: >> >> Hi all, >>> The ?intersect entry kindly points out that it discards duplicate >>> entries. I'm looking, however, to get the intersection while KEEPING >>> duplicate entries, and there are no instructions on how to accomplish this >>> using intersect(). >>> >>> Does anybody have any idea how this might be done, or am I going to need >>> to >>> program something from scratch (something like ordering the vectors and >>> then >>> looping through them)? >>> >>> >>> >>> ex: >>> >>> a <- c(2,4,2,3) >>>> b<-c(6,6,5,2,2,8,4) >>>> intersect(a,b) >>>> >>> [1] 2 4 >>> >> >> > b %in% a >> [1] FALSE FALSE FALSE TRUE TRUE FALSE TRUE >> >> # Now use logical indexing on "b" >> >> > b[b %in% a] >> [1] 2 2 4 >> >> >>> >>> >>> I'd hope the answer to be 2 2 4. >>> >>> Regards, >>> Jonathan >>> >>> [[alternative HTML version deleted]] >>> >>> ______________________________________________ >>> R-help@r-project.org mailing list >>> 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. >>> >> >> David Winsemius, MD >> West Hartford, CT >> >> > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > 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. > ______________________________________________ R-help@r-project.org mailing list 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.
