[R] stopifnot with logical(0)

[David Winsemius]

> On Dec 11, 2015, at 5:38 AM, Dario Beraldi <dario.beraldi at 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" )


> 
> stopifnot(logical(0) == 1)
> stopifnot(logical(0) == TRUE)
> stopifnot(logical(0) == FALSE)
> 
> My understanding is that logical(0) is an empty set, so I would expect the
> above tests to fail.
> 
> (I got bitten by this in a piece of code where "x" happened to be
> logical(0) and stopifnot didn't catch it)
> 
> Thanks!
> Dario
-- 

David Winsemius
Alameda, CA, USA