[R] Performance note: Preallocating helps? and two questions

[Peter Perkins]

> AUcap30<-0
> for(i in 1:length(AU))AUcap30[i]<-min(30,AU[i])

am i right in thinking that this is an implicit version of 

   for(i in 1:length(AU)) AUcap30 <- c(AUcap30, min(30,AU[i])) ?

huh.  i guess i'm surprised that this even works at all.  i don't see
any specific mention in section 3 of the FAQ, and a quick look at the R
intro documents turned up no mention either.  but i seem to remember
that it would not work in S (not that that is necessarily a reason for
it not to work in R).  i kind of _like_ having array bounds checking --
is "array extension on out of bounds indexing" really the default in R,
and is there a way to enforce array bounds checking?
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