On Wed, 6 Sep 2006, Christos Hatzis wrote: > See ?sweep > > sweep(a, 2, a[1,],"/")
That is less efficient than a/rep(a[1,], each=nrow(a)) > > -Christos > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > [EMAIL PROTECTED] > Sent: Wednesday, September 06, 2006 11:49 AM > To: [email protected] > Subject: [R] Matrix multiplication using apply() or lappy() ? > > I am trying to divide the columns of a matrix by the first row in the > matrix. > > I have tried to get this using apply and I seem to be missing a concept > regarding the apply w/o calling a function but rather command args %*% / > etc. Would using apply be more efficient than this approach? > > I have observed examples in the archives using this type of approach. Does > anybody have a snippet of a call to apply() that would accomplish this as > well? > > Thanks! > > > seed=50 > $a = array(rnorm(20),dim=c(4,5)) > $b = matrix(a[1,],dim(a)[1],dim(a)[2],byrow=T) > $a > [,1] [,2] [,3] [,4] [,5] > [1,] -1.3682810 -0.4314462 1.57572752 0.67928882 -0.3672346 [2,] 0.4328180 > 0.6556479 0.64289931 0.08983289 0.1852306 [3,] -0.8113932 0.3219253 > 0.08976065 -2.99309008 0.5818237 [4,] 1.4441013 -0.7838389 0.27655075 > 0.28488295 1.3997368 > > $a/b > [,1] [,2] [,3] [,4] [,5] > [1,] 1.0000000 1.0000000 1.00000000 1.0000000 1.000000 [2,] -0.3163225 > -1.5196515 0.40800157 0.1322455 -0.504393 [3,] 0.5930018 -0.7461539 > 0.05696457 -4.4062113 -1.584338 [4,] -1.0554128 1.8167710 0.17550671 > 0.4193841 -3.811560 > > > > ------------------------------------------------------------ > CONFIDENTIALITY NOTICE: This electronic mail transmission (i...{{dropped}} > > ______________________________________________ > [email protected] 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. > > ______________________________________________ > [email protected] 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. > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [email protected] 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.
