Bert Gunter <gunter.ber...@gene.com> writes: > ... 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:
For large named lists, unlist(l, use.names=FALSE) can have important performance consequences. individual names are created for each element, then immediately discarded -- > unlist(list(a=1:3, b=1:4)) a1 a2 a3 b1 b2 b3 b4 1 2 3 1 2 3 4 > unique(unlist(list(a=1:3, b=1:4))) [1] 1 2 3 4 > >> 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) -- Martin Morgan Computational Biology / Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109 Location: Arnold Building M1 B861 Phone: (206) 667-2793 ______________________________________________ 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.
