Using tail() for the selection is more elegant and slightly faster. > N<- 1000000 > x <- runif(N) > system.time(x[order(x)[c(N-1,N)]]) user system elapsed 1.08 0.01 1.10 > system.time(sort(x)[c(N-1,N)]) user system elapsed 0.36 0.00 0.35 > system.time(tail(sort(x), 2)) user system elapsed 0.33 0.00 0.33
HTH, Thierry ---------------------------------------------------------------------------- ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, methodology and quality assurance Gaverstraat 4 9500 Geraardsbergen Belgium tel. + 32 54/436 185 thierry.onkel...@inbo.be www.inbo.be To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher The plural of anecdote is not data. ~ Roger Brinner The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey -----Oorspronkelijk bericht----- Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] Namens andrew Verzonden: vrijdag 4 september 2009 4:24 Aan: r-help@r-project.org Onderwerp: Re: [R] Easy way to get top 2 items from vector it is speedier to use sort than a combination of [] and order: N<- 1000000 x <- runif(N) > system.time(x[order(x)[c(N-1,N)]]) user system elapsed 1.03 0.00 1.03 > system.time(sort(x)[c(N-1,N)]) user system elapsed 0.28 0.00 0.28 On Sep 4, 11:17 am, Noah Silverman <n...@smartmediacorp.com> wrote: > Phil, > > That's perfect. (For my application, I've never seen a tie. While > possible, the likelihood is almost none.) > > Thanks! > > -- > Noah > > On 9/3/09 4:29 PM, Phil Spector wrote: > > > > > Noah - > > max(x[-which.max(x)] will give you the second largest value, but > > it doesn't handle ties. > > x[order(x,decreasing=TRUE)[n]] will give you the nth largest > > value, with the same caveat regarding ties. For example, > > x[order(x,decreasing=TRUE)[1:3]] will give you the three largest > > values. > > > - Phil Spector > > Statistical Computing Facility > > Department of Statistics > > UC Berkeley > > spec...@stat.berkeley.edu > > > On Thu, 3 Sep 2009, Noah Silverman wrote: > > >> Hi, > > >> I use the max function often to find the top value from a matrix or > >> column of a data.frame. > > >> Now I'm looking to find the top 2 (or three) values from my data. > > >> I know that I could sort the list and then access the first two > >> items, but that seems like the "long way". Is there some way to > >> access "max_2" or similar? > > >> Thanks! > > >> -- > >> Noah > > >> ______________________________________________ > >> r-h...@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. > > [[alternative HTML version deleted]] > > ______________________________________________ > r-h...@r-project.org mailing > listhttps://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting > guidehttp://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. Druk dit bericht a.u.b. niet onnodig af. Please do not print this message unnecessarily. Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is door een geldig ondertekend document. The views expressed in this message and any annex are purely those of the writer and may not be regarded as stating an official position of INBO, as long as the message is not confirmed by a duly signed document. ______________________________________________ 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.