Yes, but Jeff and I advocated essentially the same approach and the difference between our versions is unimportant.
All the other approaches are at least aesthetically less desirable. One "criticism" of our solution: it relies on the underlying implementation of matrices rather than the matrix() API. In principle, the implementation could change while the API remained constant. However, the reality is that this would never happen (it would break thousands of lines of code that use this approach because R was not in the past and really still isn't entirely OO). But full disclosure demands ... Cheers, Bert -- Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." H. Gilbert Welch On Wed, May 14, 2014 at 9:07 AM, David L Carlson <dcarl...@tamu.edu> wrote: > Bert wins the race: > >> system.time(replicate(1e5, m/rep(v,e=2))) > user system elapsed > 0.25 0.00 0.25 >> system.time(replicate(1e5, m/matrix( v, ncol=ncol(m), nrow=nrow(m), >> byrow=TRUE))) > user system elapsed > 0.42 0.00 0.42 >> system.time(replicate(1e5, t(t(m)/v))) > user system elapsed > 1.31 0.00 1.33 >> system.time(replicate(1e5, sweep(m, 2, v, "/"))) > user system elapsed > 3.39 0.00 3.40 >> system.time(replicate(1e5, t(apply(m, 1, function(x) x/v)))) > user system elapsed > 5.04 0.01 5.06 > > David C > > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Jeff Newmiller > Sent: Wednesday, May 14, 2014 10:28 AM > To: carol white; carol white; r-h...@stat.math.ethz.ch > Subject: Re: [R] matrix column division by vector > > Please post in plain text... your email is getting distorted and hard to read > by the HTML. > > I don't know how to use do.call for this, but when you understand how vectors > recycle and matrices and arrays are laid out in memory (read the Introduction > to R document if not) then the following comes to mind: > > mat2 <- m / matrix( v, ncol=ncol(m), nrow=nrow(m), byrow=TRUE ) > > --------------------------------------------------------------------------- > Jeff Newmiller The ..... ..... Go Live... > DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go... > Live: OO#.. Dead: OO#.. Playing > Research Engineer (Solar/Batteries O.O#. #.O#. with > /Software/Embedded Controllers) .OO#. .OO#. rocks...1k > --------------------------------------------------------------------------- > Sent from my phone. Please excuse my brevity. > > On May 14, 2014 7:51:36 AM PDT, carol white <wht_...@yahoo.com> wrote: >>Hi, >>What is the elegant script to divide the columns of a matrix by the >>respective position of a vector elements? >> >>m=rbind(c(6,4,2),c(3,2,1)) >> >>v= c(3,2,1) >> >>res= 6/3�� 4/2� 2/1 >>������� 3/3�� 2/2 �� 1/1 >> >> >>this is correct� >>mat2 = NULL >> >>for (i in 1: ncol(m)) >> >>��� mat2 = cbind(mat2, m[,i]/ v[i]) >> >> >>but how to do more compact and elegant with for ex do.call? >> >>Many thanks >> >>Carol >> [[alternative HTML version deleted]] >> >> >> >>------------------------------------------------------------------------ >> >>______________________________________________ >>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. ______________________________________________ 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.
