unlist(..., use.names=FALSE) is heaps faster than the default unlist(..., use.names=TRUE), cf.
> z <- split(sample(1000,1e6,rep=TRUE),rep(1:1e5,10)) > system.time(y1 <- Reduce(union,z)) user system elapsed 5.98 0.00 5.89 > system.time(y2 <- unique(unlist(z))) user system elapsed 2.62 0.02 2.51 > system.time(y2b <- unique(unlist(z, use.names=FALSE))) user system elapsed 0.03 0.00 0.05 > system.time(y3 <- unique(do.call(c,z))) user system elapsed 2.28 0.03 2.37 > identical(y1,y2) [1] TRUE > identical(y1,y2b) [1] TRUE > identical(y2,y3) [1] TRUE /H On Wed, Oct 28, 2009 at 12:51 PM, Bert Gunter <gunter.ber...@gene.com> wrote: > ... 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. > ______________________________________________ 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.
