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

Martin Maechler maechler at stat.math.ethz.ch
Thu Nov 2 10:02:22 CET 2000

>>>>> "Peter" == Peter Perkins <pperkins at ucsd.edu> writes:

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

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

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

yes (as others have said on this thread).

    Peter> huh.  i guess i'm surprised that this even works at all.  i
    Peter> don't see any specific mention in section 3 of the FAQ, and a
    Peter> quick look at the R intro documents turned up no mention either.
(really, I thought it *was* there;  no time to search now..)

    Peter> but i seem to remember that it would not work in S (not that
    Peter> that is necessarily a reason for it not to work in R).
yes, it has been working in S `since ever' (even before there was S+).

    Peter> i kind of _like_ having array bounds checking -- is "array
    Peter> extension on out of bounds indexing" really the default in R,
yes (and will be)

    Peter> and is there a way to enforce array bounds checking?
not currently, but probably, there will be, by

      options(check.bound = TRUE)

which is (only partly implemented) in the current development version.

Martin Maechler <maechler at stat.math.ethz.ch>	http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><
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