On Fri, Feb 10, 2012 at 12:02:25AM -0800, xiddw wrote: > Hi everybody, > > I'm looking for an optimal way to split a big matrix (e.g. ncol = 8, > nrow=8) into small square submatrices (e.g. ncol=2, nrow=2) > > For example > > If I have > > > h > [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] > [1,] 1 9 17 25 33 41 49 57 > [2,] 2 10 18 26 34 42 50 58 > [3,] 3 11 19 27 35 43 51 59 > [4,] 4 12 20 28 36 44 52 60 > [5,] 5 13 21 29 37 45 53 61 > [6,] 6 14 22 30 38 46 54 62 > [7,] 7 15 23 31 39 47 55 63 > [8,] 8 16 24 32 40 48 56 64 > > and I want to split matriz h into 16 small submatrices: > > > g[1] > [,1] [,2] > [1,] 1 9 > [2,] 2 10 > > > g[2] > [,1] [,2] > [1,] 17 25 > [2,] 18 26 > > ... > > > g[4] > [,1] [,2] > [1,] 49 57 > [2,] 50 58 > > ... > > > g[16] > [,1] [,2] > [1,] 55 63 > [2,] 56 64 > > Always the big matrix would be a square matrix and also would have a nrow > and ncol in order of a power of two, so it always could be splitted in at > least halves. > > Until now, I'm able to split a matrix but keeping the number of original > matrix columns. > > I mean, if I want to split into 16 submatrices, using the following command > what I get its 4 lists: > But I haven't found a way to split resultant lists in order to get 4 > matrices for each list.
Hi. Try the following. k <- 3 n <- 2^k m <- 2^(k - 2) a <- matrix(1:n^2, nrow=n, ncol=n) g <- vector("list", length=16) k <- 1 for (j in 0:3) { for (i in 0:3) { g[[k]] <- a[m*i + 1:m, m*j + 1:m] k <- k + 1 } } g[1:5] [[1]] [,1] [,2] [1,] 1 9 [2,] 2 10 [[2]] [,1] [,2] [1,] 3 11 [2,] 4 12 [[3]] [,1] [,2] [1,] 5 13 [2,] 6 14 [[4]] [,1] [,2] [1,] 7 15 [2,] 8 16 [[5]] [,1] [,2] [1,] 17 25 [2,] 18 26 ... 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.