[Rd] NULL == NULL
Fri, 15 Sep 2000 08:42:44 -0700 (PDT)
On Fri, 15 Sep 2000, Martin Maechler wrote:
> gives an error in R.
> In both S+3 and S+5, it "works" by returning NULL or logical(0),
> As a consequence,
> all(x == y)
> returns TRUE in Splus, when x <- y <- NULL
> but gives an error in R.
> Do we have a good reason *not* to return logical(0) ?
I think returning logical(0) is a good idea. Having all(NULL==NULL) be
TRUE is consistent with what we do for vacuous cases of min and max.
However, a arguable reason for not doing it is that NULL is actually a
list with no elements rather than a vector with no elements, and you can't
compare lists with ==. On the gripping hand, you can't turn NULL into a
vector of length zero using eg unlist(), so the only way to get this
comparison to work is to have NULL==NULL.
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