permutation within rows of a matrix

I must be missing something. What's wrong with

?t(apply(mat, 1, sample))

?

Peter Ehlers

On 2011-11-16 12:12, Gavin Simpson wrote:

On Wed, 2011-11-16 at 14:29 -0500, R. Michael Weylandt wrote:

Suppose your matrix is called X.

? sample
X[sample(nrow(X)),]

That will shuffle the rows at random, not permute within the rows.

Here is an alternative, first using one of my packages (permute -
shameful promotion ;-) !:

mat<- matrix(sample(0:1, 100, replace = TRUE), ncol = 10)

require(permute)
perms<- shuffleSet(10, nset = 10)
## permute mat
t(sapply(seq_len(nrow(perms)),
? ? ? ? ?function(i, perms, mat) mat[i, perms[i,]],
? ? ? ? ?mat = mat, perms = perms))

If you don't want to use permute, then you can do this via standard R
functions

perms<- t(replicate(nrow(mat), sample(ncol(mat))))
## permute mat
t(sapply(seq_len(nrow(perms)),
? ? ? ? ?function(i, perms, mat) mat[i, perms[i,]],
? ? ? ? ?mat = mat, perms = perms))

HTH

G

Michael

On Wed, Nov 16, 2011 at 11:45 AM, Juan Antonio Balbuena<balbuena at uv.es>
?wrote:

Hello
This is probably a basic question but I am quite new to R.

I need to permute elements within rows of a binary matrix, such as

? ? [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
?[1,] ? ?0 ? ?0 ? ?0 ? ?0 ? ?1 ? ?0 ? ?0 ? ?0 ? ?0 ? ? 0
?[2,] ? ?0 ? ?0 ? ?1 ? ?1 ? ?0 ? ?0 ? ?0 ? ?1 ? ?1 ? ? 0
?[3,] ? ?0 ? ?1 ? ?0 ? ?0 ? ?0 ? ?0 ? ?1 ? ?0 ? ?0 ? ? 0
?[4,] ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?1 ? ?1 ? ?0 ? ? 0
?[5,] ? ?0 ? ?0 ? ?0 ? ?1 ? ?0 ? ?0 ? ?0 ? ?0 ? ?1 ? ? 0
?[6,] ? ?0 ? ?0 ? ?1 ? ?1 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ? 1
?[7,] ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ? 0
?[8,] ? ?1 ? ?1 ? ?0 ? ?1 ? ?0 ? ?0 ? ?0 ? ?1 ? ?0 ? ? 1
?[9,] ? ?1 ? ?0 ? ?0 ? ?1 ? ?0 ? ?1 ? ?0 ? ?1 ? ?0 ? ? 0
[10,] ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?0 ? ?1 ? ?0 ? ? 1


That is, elements within each row are permuted freely and independently
from
the other rows.

I see that is is workable by creating a array for each row, performing
sample and binding the arrays again, but I wonder whether there is a
more
efficient way of doing the trick.

Any help will be much appreciated.



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