[Rd] Inconsistent behaviour of is.vector? (PR#1052)
Tue, 14 Aug 2001 19:36:26 +0200
>>>>> Peter Dalgaard BSA writes:
> [R-bugs snipped from recipients]
> firstname.lastname@example.org writes:
>> R appears to allow names as attributes but nothing else, but does not
>> document this (except in the source code). Anyone want to explain why R
>> is incompatible with S? And why as.vector and is.vector are inconsistent?
>> (Note that the isas tests do not pick this up.)
> It was discussed during 1997 and 1998... Ross, Thomas, Kurt, and
> Martin seem to have been involved at some point. I'm not up to a full
> reconstruction of the discussion just now, though. One of the earliest
> cases is in this note from Thomas on the R-alpha mailing list:
I only vaguely recall this. Note however that this is in the FAQ:
* Named vectors are considered vectors in R but not in S (e.g.,
`is.vector(c(a = 1:3))' returns `FALSE' in S and `TRUE' in R).
I assume that way back then I argued that it was silly that is.vector
gave FALSE for c(a = 1) and TRUE for c(1). I think my understanding
would now be different: I would think that as.vector/is.vector should
match what the `generator' vector() does, and that cannot set names.
Otoh it cannot really set data either ...
Just in case someone brings this one up as well: we also have a diff in
is.matrix on a data frame. Splus 6 still has
> is.matrix(data.frame(x = 1:3))
and in fact is.matrix <- function(x) length(dim(x)) == 2, but I am
strongly against that: I still think that
if as.foo(x) is different from x then is.foo(x) must be false.
And that also `proves' that is.vector is wrong, as
R> x <- c(a = 1)
> On Mon, 7 Apr 1997, Ross Ihaka wrote:
>> What should is.vector do?
>> Essentially, everything in S is a vector unless it has attributes.
>> This is utterly unreasonable! Why should something stop being a
>> vector because it has a names attribute attached.
> There is method to this. Something is a vector in S if as.vector() has
> no effect on it. This includes functions but excludes matrices, vectors
> with names, and data.frames. You might then ask why as.vector() works
> the way it does and I would have no sensible explanation. A particularly
> bizarre example is
> i.e., the lm() function is a vector but the coefficient vector isn't.
> There was also some discussion in December 1998, between Kurt and
> Martin, but I cannot see how it got resolved.
> (I seem to remember that we had as.vector retaining names for a while,
> but got burned by package porting(?). Very early versions of R had
> is.vector returning true for anything that could be subscripted,
> including matrices.)
> BTW: My list archives seem to go further back than the "official"
> ones. Do we want to do anything about that? Unfortunately they are in
> Gnus's mail directory format and have been respooled so they are
> slightly out of numerical order.
> O__ ---- Peter Dalgaard Blegdamsvej 3
> c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
> (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
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