Split matrix into square submatices
On Fri, Feb 10, 2012 at 3:02 AM, xiddw <xiDDdw at gmail.com> 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.
g <- split(as.data.frame(h), (1:4)) g
$`1` ?V1 V2 V3 V4 V5 V6 V7 V8 1 ?1 ?9 17 25 33 41 49 57 5 ?5 13 21 29 37 45 53 61 $`2` ?V1 V2 V3 V4 V5 V6 V7 V8 2 ?2 10 18 26 34 42 50 58 6 ?6 14 22 30 38 46 54 62 $`3` ?V1 V2 V3 V4 V5 V6 V7 V8 3 ?3 11 19 27 35 43 51 59 7 ?7 15 23 31 39 47 55 63 $`4` ?V1 V2 V3 V4 V5 V6 V7 V8 4 ?4 12 20 28 36 44 52 60 8 ?8 16 24 32 40 48 56 64
Try this: h <- matrix(1:64, 8) # input k <- kronecker(matrix(1:16, 4, byrow = TRUE), matrix(1, 2, 2)) g <- lapply(split(h, k), matrix, nr = 2)
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