Henrique Dallazuanna wrote: > Try this: > > ave(X, rep(1:(length(X)/2), each = 2), FUN=rev) > > Also,
ix <- 2*rep(1:(length(X)/2-1), each = 2) + 2:1 X[ix] or ix <- seq_along(X) + c(1,-1) X[ix] > On Fri, Jun 27, 2008 at 11:11 AM, David Afshartous < > [EMAIL PROTECTED]> wrote: > > >> All, >> >> I have a long vector that contains an even number of entries. I'd like to >> switch the 1st and 2nd entry, the 3rd and 4th, and so on, without writing a >> loop. >> >> This code works: >> >> X = c(8, 10, 6, 3, 20, 1) >> index = c(2,1,4,3,6,5) >> X[index] >> >> But for a long list is there a way to generate the index? I can get the >> parts to the index as: >> >> index.odd = seq(1,length(X), by = 2) >> index.even = index.odd + 1 >> >> Is there a simple way to interweave them to produce the desired index? Or >> is there a better way? >> >> Cheers, >> David >> >> ______________________________________________ >> 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. > -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ 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.
