Raubertas, Richard wrote:
> 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.
Yes. There has been quite a lot discussion about 'god' during history!
Kjetil
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
>>
>>
>
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