khai wrote on 12/20/2011 01:24:10 PM:
> Thanks very much for responses. The 2 suggestions each do a part of what
I
> want. Jean's proposal permutes nonzero elements within each row but
shifts
> the location of the nonzero element around in the j slot of each i row.
And
> Douglas's idea keeps the second part but permutes the entire x slot
values.
> I'll try to see how I can combine these 2 ideas but it's not immediately
> obvious to me. =}
>
> -khai
I'm not sure what you mean by shifting "the location of the nonzero
element around in the j slot of each i row."
My code shifts the nonzero columns around at random, but keeps the zero
column in its original location. I thought that this is what you wanted
to do.
In the example below, the zero column starts as column 5 and ends as
column 5, and the nonzero columns are reordered. Columns 1, 2, 3, 4, 5, 6
end up as 2, 1, 6, 3, 5, 4.
Jean
> M1
5 x 6 sparse Matrix of class "dgTMatrix"
[1,] . 6.569 5.592 . . .
[2,] 1.163 2.688 . 1.85 . 3.217
[3,] 2.527 3.375 . . . 6.481
[4,] . . . . . 1.483
[5,] 1.004 . . . . .
> 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)
5 x 6 sparse Matrix of class "dgCMatrix"
[1,] 6.569 . . 5.592 . .
[2,] 2.688 1.163 3.217 . . 1.85
[3,] 3.375 2.527 6.481 . . .
[4,] . . 1.483 . . .
[5,] . 1.004 . . . .
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