Hi Lazarus, Sorry for my brevity before. I sent it from a phone.
# Generate dummy data matrix x <- matrix(1:100,nrow=5) # Rearrange into array; ten groups of two columns y <- array(x,c(5,2,10)) # Average columns for each submatrix apply(y,c(1,3),mean) # Average per submatrix apply(y,3,mean) Hope it helps, Tsjerk On Wed, Mar 14, 2012 at 10:01 AM, Petr Savicky <savi...@cs.cas.cz> wrote: > On Wed, Mar 14, 2012 at 03:22:39AM -0400, Lazarus Mramba wrote: >> Dear all, >> >> I have a large matrix with about 2500 variables, and 100 rows. >> >> I would like to calculate the means of the every 10 variables starting from >> 1:2500 and saving the results as a vector or matrix. >> How can I do that? >> Alternatively, How can I create 250 subset matrices in the order of >> variables 1:2500 in groups of 10 from the single matrix which had initially >> 2500 variables ? >> I guess I have to use a loop, but I can't figure out how. > > Hi. > > Try the following. I will use smaller parameters for simplicity. > > # a matrix 3 times 20 > a <- matrix(1:60, nrow=3, ncol=20) > a > > [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] > [,14] > [1,] 1 4 7 10 13 16 19 22 25 28 31 34 37 > 40 > [2,] 2 5 8 11 14 17 20 23 26 29 32 35 38 > 41 > [3,] 3 6 9 12 15 18 21 24 27 30 33 36 39 > 42 > [,15] [,16] [,17] [,18] [,19] [,20] > [1,] 43 46 49 52 55 58 > [2,] 44 47 50 53 56 59 > [3,] 45 48 51 54 57 60 > > #combine each 5 consecutive columns to a single column > dim(a) <- c(15, 4) > a > > [,1] [,2] [,3] [,4] > [1,] 1 16 31 46 > [2,] 2 17 32 47 > [3,] 3 18 33 48 > [4,] 4 19 34 49 > [5,] 5 20 35 50 > [6,] 6 21 36 51 > [7,] 7 22 37 52 > [8,] 8 23 38 53 > [9,] 9 24 39 54 > [10,] 10 25 40 55 > [11,] 11 26 41 56 > [12,] 12 27 42 57 > [13,] 13 28 43 58 > [14,] 14 29 44 59 > [15,] 15 30 45 60 > > # compute column means > colMeans(a) > > [1] 8 23 38 53 > > Hope this helps. > > Petr Savicky. > > ______________________________________________ > 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. -- Tsjerk A. Wassenaar, Ph.D. post-doctoral researcher Molecular Dynamics Group * Groningen Institute for Biomolecular Research and Biotechnology * Zernike Institute for Advanced Materials University of Groningen The Netherlands ______________________________________________ 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.