It seems to be very system dependent. Here's another take: > m <- matrix(runif(100000),1000,100) > junk <- gc() > print(system.time(for(i in 1:100) X1 <- do.call(pmax,data.frame(m)))) user system elapsed 1.53 0.01 1.57 > junk <- gc() > print(system.time(for(i in 1:100) X2 <- apply(m,1,max))) user system elapsed 1.81 0.00 1.83 >
Now what happens if you work with data frames rather than matrices: > m <- data.frame(matrix(runif(100000),1000,100)) > junk <- gc() > print(system.time(for(i in 1:100) X1 <- do.call(pmax, m))) user system elapsed 0.31 0.00 0.31 > junk <- gc() > print(system.time(for(i in 1:100) X2 <- apply(m,1,max))) user system elapsed 3.22 0.03 3.34 > Go figure! Bill Venables http://www.cmis.csiro.au/bill.venables/ -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Rolf Turner Sent: Monday, 30 March 2009 1:39 PM To: Bert Gunter Cc: 'Wacek Kusnierczyk'; r-help@r-project.org Subject: Re: [R] Matrix max by row I tried the following: m <- matrix(runif(100000),1000,100) junk <- gc() print(system.time(for(i in 1:100) X1 <- do.call(pmax,data.frame(m)))) junk <- gc() print(system.time(for(i in 1:100) X2 <- apply(m,1,max))) and got user system elapsed 2.704 0.110 2.819 user system elapsed 1.938 0.098 2.040 so unless there's something that I am misunderstanding (always a serious consideration) Wacek's apply method looks to be about 1.4 times *faster* than the do.call/pmax method. cheers, Rolf Turner On 30/03/2009, at 3:55 PM, Bert Gunter wrote: > If speed is a consideration,availing yourself of the built-in pmax() > function via > > do.call(pmax,data.frame(yourMatrix)) > > will be considerably faster for large matrices. > > If you are puzzled by why this works, it is a useful exercise in R > to figure > it out. > > Hint:The man page for ?data.frame says: > "A data frame is a list of variables of the same length with unique > row > names, given class 'data.frame'." > > Cheers, > Bert > > Bert Gunter > Genentech Nonclinical Statistics > > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On > Behalf Of Wacek Kusnierczyk > Sent: Saturday, March 28, 2009 5:22 PM > To: Ana M Aparicio Carrasco > Cc: r-help@r-project.org > Subject: Re: [R] Matrix max by row > > Ana M Aparicio Carrasco wrote: >> I need help about how to obtain the max by row in a matrix. >> For example if I have the following matrix: >> 2 5 3 >> 8 7 2 >> 1 8 4 >> >> The max by row will be: >> 5 >> 8 >> 8 >> > > matrix(apply(m, 1, max), nrow(m)) > > vQ > > ______________________________________________ > 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. ###################################################################### Attention:\ This e-mail message is privileged and confid...{{dropped:9}} ______________________________________________ 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.
