Prof Ripley, Thanks for your reply. I've inserted a couple of inline comments below.
Rich Raubertas > -----Original Message----- > From: Prof Brian Ripley [mailto:[EMAIL PROTECTED] > Sent: Wednesday, August 16, 2006 7:21 AM > To: Raubertas, Richard > Cc: r-devel@stat.math.ethz.ch > Subject: Re: [Rd] rownames() problem with 0-extent arrays (PR#9136) > > > R-bugs is not the place to ask questions, see the FAQ .... Yes, I should have sent a separate message. > > On Fri, 11 Aug 2006, [EMAIL PROTECTED] wrote: > > [...] > > > A separate but related question (not a bug) has to do with > the handling > > of dimnames for 0-extent arrays. If an array starts out > with non-NULL > > dimnames and is subscripted down to have 0-extent, the > corresponding > > component is set to NULL, rather than character(0): > > and that dimension does not have any names, so this is appropriate. I think the question of whether a dimension has names or not should be independent of the extent of that dimension. (My reason for raising the issue was that some code I was writing would be cleaner if "dimension has names" and "extent of dimension" were orthogonal concepts.) Under that premise, there is a difference between NULL (no names) and character(0) (names). It appears you don't agree with my premise, and I can see how a discussion about naming things that don't exist could get rather metaphysical. So I have worked around the issue in my code. > > > dimnames(tmp[0,,drop=FALSE]) # first component is NULL > > > > Why is that? Note that this is different from how data frames are > > handled: > > > > tmp.df <- data.frame(tmp) > > dimnames(tmp.df[0,]) # first component is character(0) > > Data frames do not have 'dimnames', and what is reported by > the accessor > function is list(row.names(x), names(x)), both of which are > required to be > character vectors. Indeed, as the help file says > > For the \code{"data.frame"} method both dimnames must be > non-null, and > the rownames must contain no duplicates nor missing values. > > > The description in ?dimnames seems to allow character(0) components > > of dimnames, > > > > "The dimnames of a matrix or array can be 'NULL' or a > list of the > > same length as 'dim(x)'. If a list, its components are either > > 'NULL' or a character vector the length of the appropriate > > dimension of 'x'." > > That is accurate. > > > yet the implementation seems to resist them: > > > > tmp2 <- tmp[0,,drop=FALSE] > > dimnames(tmp2) <- list(character(0), LETTERS[1:3]) > > dimnames(tmp2) # still NULL > > > > So my question is whether it would be reasonable to change > 'dimnames' > > and/or "dimnames<-" to use (or at least allow) character(0) > rather than > > NULL for array dimensions of 0 extent. > > Why would it be desirable to have two equivalent > representations of the > same thing (no names)? As you could easily have found out, > the C code > replaces a zero-length vector by NULL. > > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 > > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
