Hi,
I need to permute the rows of a matrix, where each row is independently
rearranged. A simple solution is this:
shuffled <- datamatrix <- matrix(1:24, ncol = 4)
for (i in 1:nrow(datamatrix)) { shuffled[i, ] <- sample(datamatrix[i, ]) }
> datamatrix
[,1] [,2] [,3] [,4]
[1,] 1 7 13 19
[2,] 2 8 14 20
[3,] 3 9 15 21
[4,] 4 10 16 22
[5,] 5 11 17 23
[6,] 6 12 18 24
> shuffled
[,1] [,2] [,3] [,4]
[1,] 7 19 13 1
[2,] 2 8 14 20
[3,] 15 3 9 21
[4,] 22 10 16 4
[5,] 5 11 17 23
[6,] 24 6 12 18
However, I need to perform quite a lot of these permutations, and I was
wondering whether anyone knows of a faster way of doing this. Something that
might not involve a "for" loop, for instance?
-Diogo
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