OK thanks, I thought it probably was, but always worth asking. the multiplication of the columns of M2 by V2 is as intended - not matrix multiplication.
On Tue, 14 Sept 2021 at 17:49, Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote: > That is about as fast as it can be done. However you may be able to avoid > doing it at all if you fold V2 into a matrix instead. Did you mean to use > matrix multiplication in your calculation of M3? > > On September 13, 2021 11:48:48 PM PDT, nevil amos <nevil.a...@gmail.com> > wrote: > >Hi is there a faster way to "extract" rows of a matrix many times to for a > >longer matrix based in a vector or for indices than M[ V, ] > > > >I need to "expand" ( rather than subset) a matrix M of 10-100,000 rows x > >~50 columns to produce a matrix with a greater number (10^6-10^8) of rows > >using a vector V containing the 10^6 -10^8 values that are the indices of > >the rows of M. the output matrix M2 is then multiplied by another vector > V2 > >With the same length as V. > > > >Is there a faster way to achieve these calculations (which are by far the > >slowest portion of a function looped 1000s of times? than the standard M2 > ><- M[ V, ] and M3<-M2*V2, the two calculations are taking a similar time, > >Matrix M also changes for each loop. > > > > > >M<-matrix(runif(50*10000,0,100),nrow=10000,ncol=50) > >x = 10^7 > >V<-sample(1:10000,x,replace=T) > >V2<-(sample(c(1,NA),x,replace=T)) > >print<-(microbenchmark( > >M2<-M[V,], > >M3<-M2*V2, > >times=5,unit = "ms")) > > > > > > > >thanks for any suggestions > > > >Nevil Amos > > > > [[alternative HTML version deleted]] > > > >______________________________________________ > >R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >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. > > -- > Sent from my phone. Please excuse my brevity. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
