[Rd] nrow(rbind(character(), character())) returns 2 (as documented but very unintuitive, IMHO)

[Gabriel Becker]

Hi Hadley,

Thanks for the counterpoint. Response below.

On Thu, May 16, 2019 at 1:59 PM Hadley Wickham <h.wickham using gmail.com> wrote:

> The existing behaviour seems inutitive to me. I would consider these
> invariants for n vector x_i's each with size m:
>
> * nrow(rbind(x_1, x_2, ..., x_n)) equals n
>

Personally, no I wouldn't. I would consider m==0 a degenerate case, where
there is no data, but I personally find matrices (or data.frames) with rows
but no columns a very strange concept. The converse is not true, I
understand the utility of columns but no rows, particularly in the
data.frame case, but rows with no columns are observations we didn't
observe anything about. Strange, imho.

Also, I know that you said *each with size m*, but the generalization would
be

for n vectors with m = max(length(x_i))
nrow(rbind(x_1, ..., x_n)) = m

And that is the behavior now as documented, but *only* when length(x_i) >0
for all i (or, currently, when m == 0, so all vectors are length 0).

> nrow(rbind(1:5, numeric()))

[1] 1


So that is where I was coming from. Length-zero vectors don't add rows
because they contain no observed information.

I do see where you'er coming from, but it does make interrogating
nrow(rbind(x_1, ..., x_n)) NOT mean  (give me the number of observations
for which I have data), which is what it means in non-degenerate contexts,
and that seems pretty important too.

Robin does also have an interesting point below about argument names, but
I'll leave that for another mail.

Best,
~G

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