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.