R-alpha: ==NULL
Thomas Lumley
thomas@biostat.washington.edu
Thu, 1 May 1997 09:28:48 -0700 (PDT)
On Thu, 1 May 1997, Martin Maechler wrote:
> >>>>> "Tom" == Thomas Lumley <thomas@biostat.washington.edu> writes:
^^^^^ Aaargh! Not "Tom", please.
>
> Tom> Any comparison with NULL generates an error Error: comparison is
> Tom> possible only for vector types whereas in S(-PLUS) it gives NA,
> Tom> which seems more sensible.
>
> Tom> Along similar lines, comparison with a length 0 vector returns
> Tom> logical(0) in R but NA in S.
>
> Is n't logical(0) more logical than NA ?
I didn't (previously) make any comment on this -- I only said that NA was
more logical than an error message. However, the advantage of returning
NA is that NA | TRUE is TRUE, NA & FALSE is FALSE, which doesn't happen
with logical(0). Also, from a compatibility point of view one of them is
tested with is.na(), the other with length(), so it can matter which one
you use. Of course no-one should deliberately write code where it
matters, but these things happen.
It seems in fact that logical(0) | TRUE causes R to freeze (R0.49,
sparc solaris).
Thomas Lumley
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