Hi all,
so I've known for a while that NROW(NULL) gives 0, where nrow(NULL) gives
an error, so I naively expected NCOL to do the same.
Of course, it does not, and is documented* (more on this in a bit) as not
doing so. For those reading without the documentation open, it gives 1.
The relevant doc states:
?nrow? and ?ncol? return the number of rows or columns present in ?x?.
?NCOL? and ?NROW? do the same treating a vector as 1-column matrix, even a
0-length vector, compatibly with ?as.matrix()? or ?cbind()?, see the
example.
But there are a couple of fiddly bits here. First is that it says "even a
0-length *vector*" (emphasis mine), but we have
> is.vector(NULL)
[1] FALSE
As opposed, of course, to, e.g., numeric(0).
Next is the claim of compatibility with as.matrix and cbind, but in both my
released version of R (4.0.2) and devel that I just built from trunk, we
have
> NCOL(NULL)
[1] 1
> cbind(NULL)
NULL
> as.matrix(NULL)
*Error in array(x, c(length(x), 1L), if (!is.null(names(x)))
list(names(x), : *
* 'data' must be of a vector type, was 'NULL'*
So in fact each function is treating NULL completely differently.
The fix (to change behavior or to add a mention in the documentation that
NULL is treated as a 0-length vector) would be easy to do, should I file a
bug with a patch for this?
Best,
~G
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