Re: [R] odd feature

From: Martin Maechler <maechler_at_stat.math.ethz.ch>
Date: Tue 23 May 2006 - 01:40:53 EST

>>>>> "Gabor" == Gabor Grothendieck <ggrothendieck@gmail.com> >>>>> on Mon, 22 May 2006 11:34:09 -0400 writes:

    Gabor> On 5/22/06, Martin Maechler <maechler@stat.math.ethz.ch> wrote:

>> >>>>> "TL" == Thomas Lumley <tlumley@u.washington.edu>
>> >>>>> on Mon, 22 May 2006 07:09:09 -0700 (PDT) writes:
>>
    TL> On Mon, 22 May 2006, Gabor Grothendieck wrote:
>> >> Due to lazy evaluation, I don't think a and b are fully evaluated:
>> >>
>> >>> ifelse(1, a <- 1, b <- 2)
>> >> [1] 1
>> >>> a
>> >> [1] 1
>> >>> b
>> >> Error: object "b" not found
>>
    TL> yes. If you look at the code for ifelse() it evaluates
    TL> the second argument if any test values are TRUE and the
    TL> third argument if any test values are FALSE, so in the
    TL> scalar case it does not evaluate both arguments.

>>
>> yes.
>> And (Gabor), if you recall what I said earlier, it's pretty clear
>> that I would not even *consider* using ifelse() in the scalar
>> case. So my original statement was about the case ifelse() is
>> designed for: The non-trivial vector case, and there my
>> statement of "fully evaluated" does apply.
>>
>> Martin
>>

    Gabor> I don't think they are fully evaluated in the vector case either:

>> ifelse(rep(TRUE,4), a <- 1:4, b <- 1:4)
    Gabor> [1] 1 2 3 4
>> a

    Gabor> [1] 1 2 3 4
>> b

    Gabor> Error: object "b" not found

PLEASE !!!!


I said "non-trivial" above !!!!!!!!
Martin



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue May 23 02:12:39 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Tue 23 May 2006 - 04:10:23 EST.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.