non-consing count

Is performance a concern?  How often are you going to do it and what
other parts of your script also take longer?  Why are you concerned
about allocating/discarding two vectors?

I think Sam's question was about additional memory introduced by which.

For example:

x  <- c(1, 0, 0, 1, 0, 2, 0)
wx <- which(x==0)
object.size(wx)

56 bytes

object.size(x)

104 bytes


If you have very large vector, a time series for example. This would
make a lot of
difference. I am not sure how 'sum' internally handles, but  As I said
earlier, a special function
in C might be faster then length-which couple or sum, that counts
occurrences as it goes, so it could
get the result in one go, maybe like  x %count% 0. One can implement a
recursive function
to do this in R interpreter level, but not sure about recursion depth
memory requirement.