khai wrote on 12/19/2011 11:26:55 PM:
> Hi,
>
> I'm very new to working with sparse matrices and would like to know how
I
> can column permute a sparse matrix. Here is a small example:
>
> > M1 <-
> > spMatrix(nrow=5,ncol=6,i=sample(5,15,replace=TRUE),j=sample(6,
> 15,replace=TRUE),x=round_any(rnorm(15,2),0.001))
> > M1
> 5 x 6 sparse Matrix of class "dgTMatrix"
>
> [1,] 2.983 . 1.656 5.003 . .
> [2,] . . 2.990 . . .
> [3,] . 0.592 5.349 1.115 . .
> [4,] 1.836 . 2.804 . . .
> [5,] . 6.961 . . . 1.077
>
> I know I can permute entire columns this way
>
> > M1[,sample(6,6)]
> 5 x 6 sparse Matrix of class "dgTMatrix"
>
> [1,] 5.003 . . . 1.656 2.983
> [2,] . . . . 2.990 .
> [3,] 1.115 0.592 . . 5.349 .
> [4,] . . . . 2.804 1.836
> [5,] . 6.961 1.077 . . .
>
> But I would like the new sparse matrix to look like this...where only
the
> nonzero elements are permuted.
>
> [1,] 1.656 . 5.003 2.983 . .
> [2,] . . 2.990 . . .
> [3,] . 5.349 1.115 0.592 . .
> [4,] 2.804 . 1.836 . . .
> [5,] . 1.077 . . . 6.961
>
> Thanks in advance for any advice!
I don't have experience with sparse matrices, but I was able to get this
to work by converting the sparse matrix to a "base" matrix and back again.
library(Matrix)
nonzero.cols <- !apply(M1==0, 2, all)
M2 <- as.matrix(M1)
reord <- sample(seq(dim(M1)[2])[nonzero.cols])
M2[, nonzero.cols] <- as.matrix(M1[, reord])
Matrix(M2, sparse=TRUE)
Jean
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