The original post is ambiguous: do you want to find the intersection or do you want to find whether a prespecified set is in the intersection? Patrick provided you an answer to the latter while you provided an answer to the former. Actually, I thought using table as you did (mod the need for no replicates) was clever. A more direct but I think considerably slower approach would be to use intersect() in a loop:
inall<-intersect(foo[[1]],foo[[,2]]) for(i in seq(3, to=length(foo))inall<-intersect(inall,foo[[i]]) I suspect you already thought of this and rejected it. Other than transparency, I think the only advantage it has is that it will work for something other than lists of numerics, e.g. it will work for lists of factors, which the table() solution would not. -- Bert -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Patrick Burns Sent: Friday, April 07, 2006 12:04 PM To: Andy Bunn Cc: R-Help Subject: Re: [R] finding common elements in a list Here is one solution: > all(unlist(lapply(foo, function(x) c(2,3) %in% x))) [1] TRUE This doesn't have the restriction of assuming that the components of the list have unique elements, as the original solution does. Patrick Burns [EMAIL PROTECTED] +44 (0)20 8525 0696 http://www.burns-stat.com (home of S Poetry and "A Guide for the Unwilling S User") Andy Bunn wrote: >Suppose I have a list where I want to extract only the elements that occur >in every component. For instance in the list foo I want to know that the >numbers 2 and 3 occur in every component. The solution I have seems >unnecessarily clunky. TIA, Andy > > foo <- list(x = 1:10, y=2:11, z=1:3) > bar <-unlist(foo) > bartab <- table(bar) > as.numeric(names(bartab)[bartab==length(foo)]) > > [[alternative HTML version deleted]] > >______________________________________________ >[email protected] mailing list >https://stat.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > > > > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
