... and just for amusement: unique(do.call(c,l)) The do.call and unlist approaches should be faster than Reduce; do.call _may_ be marginally faster than unlist. Here's a timing comparison:
> z <- split(sample(1000,1e6,rep=TRUE),rep(1:1e5,10)) > length(z) [1] 100000 ## the comparisons: > system.time(y1 <- Reduce(union,z)) user system elapsed 5.02 0.00 5.03 > system.time(y2 <- unique(unlist(z))) user system elapsed 1.92 0.00 1.92 > system.time(y3 <- unique(do.call(c,z))) user system elapsed 1.75 0.00 1.75 > identical(y1,y2) [1] TRUE > identical(y2,y3) [1] TRUE Obviously, this is unlikely to matter for any reasonable size dataset, but maybe it's instructive. Of course, Reduce wins the RGolf contest ;-) Bert Gunter Genentech Nonclinical Biostatistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Ben Bolker Sent: Wednesday, October 28, 2009 12:27 PM To: r-help@r-project.org Subject: Re: [R] How to union the elements in a list? Peng Yu wrote: > > Suppose that I have a list of vectors. I want to compute the union of > all the vectors in the list. I could use 'for' loop to do so. But I'm > wondering what would be a better solution that does not need a 'for' > loop. > > l=list(a=c(1,3,4), b=c(1,3,6), c=c(1,3,7), ....) > > Reduce(union,l) -- View this message in context: http://www.nabble.com/How-to-union-the-elements-in-a-list--tp26100375p261006 84.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
