[Adding R-help back, as you did later.]
On Wed, 7 Nov 2007, Charilaos Skiadas wrote:
> On Nov 7, 2007, at 2:51 AM, Prof Brian Ripley wrote:
>
>> On Tue, 6 Nov 2007, Charilaos Skiadas wrote:
>>
>>> Hello all,
>>>
>>> I ran into the following, to me unexpected, behavior. I have (for
>>> reasons that don't necessarily pertain to the question at hand, hence
>>> I won't go into them) the need/desire to use an empty string for the
>>> name of a vector entry.
>>
>> The 'R Languge Definition' says
>>
>> The string "" is treated specially: it indicates `no name' and matches
>> no element (not even those without a name).
>>
>> and from ?names
>>
>> The name \code{""} is special: it is used to indicate that there is no
>> name associated with an element of a (atomic or generic) vector.
>> Subscripting by \code{""} will match nothing (not even elements which
>> have no name).
>>
>> so it should perhaps have been expected.
>
> It should indeed, if I had looked at ?names, which I should have thought of
> doing. I wonder why ?"[" doesn't mention it though, especially the part
> about: "Subscripting by "" will match nothing (not even elements which have
> no name)."
Well, the help page of `[` is complex enough already, there was a link to
the page for names, and this doesn't seem to have bitten many people.
However, I have already added the information for the next version since
there were other facts about character indexing that were not there and I
created a new section for them. However we try to organize it,
information overload seems to be a problem for that help page.
I suspect that not everyone who has worked on the code/documentation was
aware of the special status of "" ....
> What are the reasons for treating "" in a special way, btw? i.e. can't we use
> NA to indicate "no name"? (Hm, come to think of it, NA means more that we
> don't know the name, not that there isn't a name. So perhaps it makes sense
> after all.)
It long predates the availability of character NAs (which S did not have),
and as you say, it is not quite the same.
[...]
--
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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