On Sat, Dec 12, 2015 at 3:54 AM, Martin Maechler
<maech...@stat.math.ethz.ch> wrote:
>>>>>> Henrik Bengtsson <henrik.bengts...@gmail.com>
>>>>>> on Fri, 11 Dec 2015 08:20:55 -0800 writes:
>
> > On Fri, Dec 11, 2015 at 8:10 AM, David Winsemius
> <dwinsem...@comcast.net> wrote:
> >>
> >>> On Dec 11, 2015, at 5:38 AM, Dario Beraldi <dario.bera...@gmail.com>
> wrote:
> >>>
> >>> Hi All,
> >>>
> >>> I'd like to understand the reason why stopifnot(logical(0) == x)
> doesn't
> >>> (never?) throw an exception, at least in these cases:
> >>
> >> The usual way to test for a length-0 logical object is to use length():
> >>
> >> x <- logical(0)
> >>
> >> stopifnot( !length(x) & mode(x)=="logical" )
>
> > I found
>
> > stopifnot(!length(x), mode(x) == "logical")
>
> > more helpful when troubleshooting, because it will tell you whether
> > it's !length(x) or mode(x) == "logical" that is FALSE. It's as if you
> > wrote:
>
> > stopifnot(!length(x))
> > stopifnot(mode(x) == "logical")
>
> > /Henrik
>
> Yes, indeed, thank you Henrik --- and Jeff Newmiller who's nice
> humorous reply added other relevant points.
>
> As author stopifnot(), I do agree with Dario's "gut feeling"
> that stopifnot() "somehow ought to do the right thing"
> in cases such as
>
> stopifnot(dim(x) == c(3,4))
>
> which is really subtle version of his cases
> {But the gut feeling is wrong, as I argue from now on}.
Personally, I think the problem there is that people forget that == is
vectorised, and for a non-vectorised equality check you really should
use identical:
stopifnot(identical(dim(x), c(3,4)))
Hadley
--
http://had.co.nz/
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