Thanks for this. I was afraid someone was going to say this ... Does this mean the only way of getting this to run faster is by moving to C code? The cases I'm thinking of applying this in have dimensions of A that are much larger than the example, eg n by n by T where n has a max of 10 or so but T could be hundreds or even thousands. Best, Ingmar
On Mar 27, 2008, at 12:11 AM, <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> wrote: > If you have lots of memory there is an obvious strategy: > > d12 <- prod(dim(A)[1:2]) > A <- A * array(rep(B, each = d12), dim = dim(A)) > > I don't really see much wrong with the obvious for() loop, though: > > for(b in 1:length(B)) A[,,b] <- A[,,b] * B[b] > > > Bill Venables > CSIRO Laboratories > PO Box 120, Cleveland, 4163 > AUSTRALIA > Office Phone (email preferred): +61 7 3826 7251 > Fax (if absolutely necessary): +61 7 3826 7304 > Mobile: +61 4 8819 4402 > Home Phone: +61 7 3286 7700 > mailto:[EMAIL PROTECTED] > http://www.cmis.csiro.au/bill.venables/ > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > project.org] > On Behalf Of Ingmar Visser > Sent: Thursday, 27 March 2008 7:58 AM > To: R-help@r-project.org > Subject: [R] avoiding loops > > Hi, > I need to compute an array from a matrix and an array: > > A <- array(1:20,c(2,2,5)) > B <- matrix(1:10,5) > > And I would like the result to be an array consisting of the > following: > > rbind(A[1,,1]*B[1,], > A[2,,1]*B[1,]) > > rbind(A[1,,2]*B[2,], > A[2,,2]*B[2,]) > > rbind(A[1,,3]*B[2,], > A[2,,3]*B[2,]) > > etc. > > Hence the result should have the same dimension as A, ie a series of > 2 by 2 matrices. > > Short of a for loop over the the last index of A I have struggled > with versions of apply but > to no avail ... > > Any insights much appreciated, > > Best, Ingmar > > ______________________________________________ > R-help@r-project.org 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. > > ______________________________________________ R-help@r-project.org 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.
