On Jul 17, 2013, at 3:04 PM, Witold E Wolski <wewol...@gmail.com> wrote:
> How can id do this efficiently in R ? > > 1 0 0 > 0 2 0 > 0 0 3 > > > rotate right > 0 0 1 > 0 2 0 > 3 0 0 > rotate left > 0 0 3 > 0 2 0 > 1 0 0 > > What I want to do is described here: > http://stackoverflow.com/questions/13049575/r-min-max-and-mean-of-off-diagonal-elements-in-a-matrix > > but I want do to it for all off-anti-diagonals. > > I am also concerned that the method described on stackoverflow isn't > necessarily efficient. > I work with matrices of size 3k * 3k. > I did not take the time to review in detail the solutions on SO, but here is one approach for rotation, albeit, not fully tested: > mat [,1] [,2] [,3] [1,] 1 0 0 [2,] 0 2 0 [3,] 0 0 3 # Rotate right > t(mat)[, ncol(mat):1] [,1] [,2] [,3] [1,] 0 0 1 [2,] 0 2 0 [3,] 3 0 0 # Rotate left > t(mat)[nrow(mat):1, ] [,1] [,2] [,3] [1,] 0 0 3 [2,] 0 2 0 [3,] 1 0 0 big.mat <- matrix(rep(0, 3000 * 3000), ncol = 3000) > str(big.mat) num [1:3000, 1:3000] 0 0 0 0 0 0 0 0 0 0 ... > system.time(mat.right <- t(big.mat)[, ncol(big.mat):1]) user system elapsed 0.273 0.000 0.273 > system.time(mat.left <- t(big.mat)[nrow(big.mat):1], ) user system elapsed 0.094 0.000 0.099 Regards, Marc Schwartz ______________________________________________ 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.
