[R] non-consing count

[Suzen, Mehmet]

My 2 cents:

AFAIK both which and length are from C compiled code:

http://cran.r-project.org/doc/manuals/r-release/R-ints.html#g_t_002eInternal-vs-_002ePrimitive

so they must be quite efficient ie .Primitive and .Internal. Probably
combination
of this with a pattern in C would be more memory efficient to count
patterns, but
would that make sense? Because in general if you look for a pattern in
a vector, you
need to know where it is, hence which operation, at least for debugging/testing
purposes...

On 4 January 2013 16:30, Sam Steingold <sds at gnu.org> wrote:
> Hi,
> to count vector elements with some property, the standard idiom seems to
> be length(which):
> --8<---------------cut here---------------start------------->8---
> x <- c(1,1,0,0,0)
> count.0 <- length(which(x == 0))
> --8<---------------cut here---------------end--------------->8---
> however, this approach allocates and discards 2 vectors: a logical
> vector of length=length(x) and an integer vector in which.
> is there a cheaper alternative?
> Thanks!
>
> --
> Sam Steingold (http://sds.podval.org/) on Ubuntu 12.04 (precise) X 11.0.11103000
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