R help - Jun 2011 - columnwise nnzero for dgCMatrix

Hi R users,

I want to know whether there is a fast method to compute the nonzeroes for
each column of dgCMatrix.

For summation or average I can use colSums or colMeans. To count the
non-zeroes I write a function

colCounts <- function(Mat) {
    M1 <- apply(Mat, MARGIN=2, FUN=nnzero)
}

But it seems this is quite slow because the apply function would transform a
dgCMatrix to a matrix.

So I come here to ask if there is anybody know some fast method.

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Hi:

What about

colSums(mymat != 0)

?

# Example:
x <- matrix(sample(c(-1, 0, 1, 2), 100, replace = TRUE, prob = c(0.1,
0.8, 0.07, 0.03)),
              nrow = 25)
which(x != 0)  # 17 nonzero elements in this matrix
 [1]  9 17 27 32 36 41 44 45 49 50 62 67 68 72 76 78 82
colSums(x != 0)
[1] 2 8 4 3


Dennis

On Sun, Jun 26, 2011 at 3:15 AM, C6H5NO2 <C6H5NO2 at gmail.com>
wrote:
> Hi R users,
>
> I want to know whether there is a fast method to compute the nonzeroes for
> each column of dgCMatrix.
>
> For summation or average I can use colSums or colMeans. To count the
> non-zeroes I write a function
>
> colCounts <- function(Mat) {
> ? ?M1 <- apply(Mat, MARGIN=2, FUN=nnzero)
> }
>
> But it seems this is quite slow because the apply function would transform
a
> dgCMatrix to a matrix.
>
> So I come here to ask if there is anybody know some fast method.
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/columnwise-nnzero-for-dgCMatrix-tp3625726p3625726.html
> Sent from the R help mailing list archive at Nabble.com.
>
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