No loops necessary. Use array indexing (see ?"[", of course -- the section on matrices and arrays)
set.seed(123) A <- matrix(sample(1:10), nrow = 5) B <- matrix(c(sample(1:5), sample(1:5)), nrow =5, byrow = FALSE) ## The following could be a 1-liner, but I broke it out for clarity. ix <- cbind(as.vector(B), rep(1:2, e=5)) ix matrix(A[ix], ncol =2) Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Mon, Oct 28, 2019 at 1:48 PM Linus Chen <linus.l.c...@gmail.com> wrote: > Hi Jinsong, > > In such a case I think explicit loop IS the most elegant solution. > for(i in 1:2) A[,i] <- A[,i][B[,i]] > > Linus > > On Fri, 11 Oct 2019 at 11:44, Jinsong Zhao <jsz...@yeah.net> wrote: > > > > Hi there, > > > > I have two matrices, A and B. The columns of B is the index of the > > corresponding columns of A. I hope to rearrange of A by B. A minimal > > example is following: > > > > > set.seed(123) > > > A <- matrix(sample(1:10), nrow = 5) > > > B <- matrix(c(sample(1:5), sample(1:5)), nrow =5, byrow = FALSE) > > > A > > [,1] [,2] > > [1,] 3 9 > > [2,] 10 1 > > [3,] 2 7 > > [4,] 8 5 > > [5,] 6 4 > > > B > > [,1] [,2] > > [1,] 2 1 > > [2,] 3 4 > > [3,] 1 5 > > [4,] 4 3 > > [5,] 5 2 > > > A[,1] <- A[,1][B[,1]] > > > A[,2] <- A[,2][B[,2]] > > > A > > [,1] [,2] > > [1,] 10 9 > > [2,] 2 5 > > [3,] 3 4 > > [4,] 8 7 > > [5,] 6 1 > > > > My question is whether there is any elegant or generalized way to > replace: > > > > > A[,1] <- A[,1][B[,1]] > > > A[,2] <- A[,2][B[,2]] > > > > Thanks in advance. > > > > PS., I know how to do the above thing by loop. > > > > Best, > > Jinsong > > > > ______________________________________________ > > 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. > > ______________________________________________ > 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. > [[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.
