[R] Filter a matrix with a matrix HELP!

[R. Michael Weylandt]

On Thu, Aug 2, 2012 at 8:16 AM, Cloneberry <cloneberry at gmail.com> wrote:
> Hi,
> just during these vacation days, I'm trying to approach with multicore
> package
> and I have some troubles with foreach.
> What I'm trying to do is to extract a data in coordinate (ii,jj) from a
> matrix2,
> only if the data in the same coordinate in matrix1 is ==1.

I think you're making this far too hard -- subsetting is a relatively
cheap operation and shouldn't require this sort of parallelization:

matrix2[matrix1 == 1]

matrix1 == 1 will create a boolean (TRUE/FALSE) matrix which you then
use to pick out a subset of matrix2.

Best,
Michael

> Make this with a nested "for" take a lot of time because I have thousand of
> values.
>
> ex.
> Binary_hex = NULL
> foreach(ii=1:nrow(matrix2)) %:% foreach(jj=1:ncol(matrix2)) %dopar%
> {when(matrix2[ii,jj] == 1) %:% {Binary_hex <- c(Binary_hex,
> matrix1[ii,jj])}}
>
> During this operation... computer don't work in multicore and the process
> take a lot of time,
> just like a simple nested for. I think the mistake is in the "when"
> parameter because if I substitute
> the "when" with another function (like "sqrt") it work greatly and fast.
> Please, give me some suggestion, also with different way.
> Thank you in advance.
> Max
>
>
>
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