Re: [R] odd feature

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Tue 23 May 2006 - 01:34:09 EST

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
>

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

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

[1] 1 2 3 4
> b

Error: object "b" not found



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 02:47:10 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.