False premise: rep works fine
Mout2 <- cbind(M[ rep(seq.int(nrow(M)),M[,"k"]),
c("x","y","z")],unlist(lapply(M[,"k"],seq.int)))
On March 31, 2020 6:18:37 PM PDT, nevil amos <nevil.a...@gmail.com> wrote:
>Hi
>
>I can achieve this using two for loops but it is slow I need to do
>this on
>many matrices with tens of millions of rows of x,y,z and k
>
>What is a faster method to achieve this, I cannot use rep as j changes
>in
>each row of the new matrix
>###############################################
>M<-matrix(c(1,2,3,4,1,2,3,4,1,2,3,4, 2, 1, 3, 2
>), 4,4, dimnames = list(NULL, c("x", "y", "z","k")))
>
>Print(M)
>#Create matrix (Mout) in this case 8 rows with x,y,z in each row of M
>#repeated k times with column j numbered from 1:k
># ! can do with nested loops but this is very slow ( example below)
>#How do I acheive this quickly without loops?
>Mout<-NULL
>
>for(i in 1:nrow(M)){
> a=M[i,c("x","y","z")]
> for (j in 1:M[i,"k"]){
> b=c(a,j)
> Mout<-rbind(Mout,b)
> }
>}
>colnames(Mout)[4]<-"j"
>print(Mout)
>
>#########################################################
>
>Thanks
>
>Nevil Amos
>
> [[alternative HTML version deleted]]
>
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--
Sent from my phone. Please excuse my brevity.
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
