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 * ncol(rbind(x_1, x_2, ..., x_n)) equals m Additionally, wouldn't you expect rbind(x_1[i], x_2[i]) to equal rbind(x_1, x_2)[, i, drop = FALSE] ? Hadley On Thu, May 16, 2019 at 3:26 PM Gabriel Becker <gabembec...@gmail.com> wrote: > > Hi all, > > Apologies if this has been asked before (a quick google didn't find it for > me),and I know this is a case of behaving as documented but its so > unintuitive (to me at least) that I figured I'd bring it up here anyway. I > figure its probably going to not be changed, but I'm happy to submit a > patch if this is something R-core feels can/should change. > > So I recently got bitten by the fact that > > > nrow(rbind(character(), character())) > > [1] 2 > > > I was checking whether the result of an rbind call had more than one row, > and that unexpected returned true, causing all sorts of shenanigans > downstream as I'm sure you can imagine. > > Now I know that from ?rbind > > For ‘cbind’ (‘rbind’), vectors of zero length (including ‘NULL’) > > > > are ignored unless the result would have zero rows (columns), for > > > > S compatibility. (Zero-extent matrices do not occur in S3 and are > > > > not ignored in R.) > > > > But there's a couple of things here. First, for the rowbind case this > reads as "if there would be zero columns, the vectors will not be > ignored". This wording implies to me that not ignoring the vectors is a > remedy to the "problem" of the potential for a zero-column return, but > thats not the case. The result still has 0 columns, it just does not also > have zero rows. So even if the behavior is not changed, perhaps this > wording can be massaged for clarity? > > The other issue, which I admit is likely a problem with my intuition, but > which I don't think I'm alone in having, is that even if I can't have a 0x0 > matrix (which is what I'd prefer) I would have expected/preferred a 1x0 > matrix, the reasoning being that if we must avoid a 0x0 return value, we > would do the minimum required to avoid, which is to not ignore the first > length 0 vector, to ensure a non-zero-extent matrix, but then ignore the > remaining ones as they contain information for 0 new rows. > > Of course I can program around this now that I know the behavior, but > again, its so unintuitive (even for someone with a fairly well developed > intuition for R's sometimes "quirky" behavior) that I figured I'd bring it > up. > > Thoughts? > > Best, > ~G > > [[alternative HTML version deleted]] > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel -- http://hadley.nz ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
