Hello Demi
The trick for array indexing on an array A, where length(dim(A))==n, is to use an n-column matrix M to extract the elements by rows of M. If I understand correctly, the following should help: > A <- array(1:18,c(3,3,2)) > x <- 2:3 > y <- 1:2 > A[cbind(x,y,1)] [1] 2 6 You may find the following useful too: > A[as.matrix(cbind(1,expand.grid(x,y)))] [1] 4 7 13 16 > best rksh On 1 Feb 2007, at 13:34, Demi Anderson wrote: > Dear R-community, > > I have some trouble with index mappings for arrays. If, for example, > I have the array > > R> A <- array(1:9, c(3,3,2)) > > and two index mappings both of same size > > R> x <- c(2, 3) > R> y <- c(1, 2) > > Now I want to access the elements (A[1, x[i], y[i]])_i of A, i.e. > A[1, x[1], y[1]] = A[1, 2, 1] and A[1, x[2], y[2]] = A[1, 3, 2]. > > If I use > > R> A[1, x, y] > > I would get every combinations of indices of all elements of x and y > i.e. A[1, x[1], y[1]], A[1, x[1], y[2]], A[1, x[2], y[1]] and A[1, > x[2], y[2]]. But how can I access the elements (A[1, x[i], y[i]])_i. > My arrays dimensions are actually large in the second > component (for example the dimension might be 10*10000*10) so I'm > looking for a method avoiding loops. > > The question is probably trivial for you, but I just could not > figure it out. So sorry for bugging you and many thanks in advance > for any help. > > Best wishes, Demi Anderson. > -- > "Feel free" - 10 GB Mailbox, 100 FreeSMS/Monat ... > > ______________________________________________ > [email protected] 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. -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 -- This e-mail (and any attachments) is confidential and intend...{{dropped}} ______________________________________________ [email protected] 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.
