[Rd] x <- 1:2; dim(x) <- 2? A vector or not?
Tony Plate
tplate at acm.org
Fri Jan 16 21:10:04 CET 2009
Martin Maechler wrote:
>>>>>> "PatB" == Patrick Burns <pburns at pburns.seanet.com>
>>>>>> on Tue, 13 Jan 2009 17:00:40 +0000 writes:
>>>>>>
>
> PatB> Henrik Bengtsson wrote:
> >> Hi.
> >>
> >> On Mon, Jan 12, 2009 at 11:58 PM, Prof Brian Ripley
> >> <ripley at stats.ox.ac.uk> wrote:
> >>
> >>> What you have is a one-dimensional array: they crop up
> >>> in R most often from table() in my experience.
> >>>
> >>>
> >>>> f <- table(rpois(100, 4)) str(f)
> >>>>
> >>> 'table' int [, 1:10] 2 6 18 21 13 16 13 4 3 4 - attr(*,
> >>> "dimnames")=List of 1 ..$ : chr [1:10] "0" "1" "2" "3"
> >>> ...
> >>>
> >>> and yes, f is an atmoic vector and yes, str()'s notation
> >>> is confusing here but if it did [1:10] you would not
> >>> know it was an array. I recall discussing this with
> >>> Martin Maechler (str's author) last century, and I've
> >>> just checked that R 2.0.0 did the same.
> >>>
> >>> The place in which one-dimensional arrays differ from
> >>> normal vectors is how names are handled: notice that my
> >>> example has dimnames not names, and ?names says
> >>>
> >>> For a one-dimensional array the 'names' attribute really
> >>> is 'dimnames[[1]]'.
> >>>
> >>
> >> Thanks for this explanation. One could then argue that
> >> [1:10,] is somewhat better than [,1:10], but that is just polish.
>
> yes. And honestly I don't remember anymore why I chose the
> "[,1:n]" notation. It definitely was there already before R
> came into existence, as S also has had one-dimensional arrays,
> and I programmed the first version of str() in 1990.
>
> PatB> Perhaps it could be:
>
> PatB> [1:10(,)]
>
> PatB> That is weird enough that it should not lead people to
> PatB> believe that it is a matrix. But might prompt them a
> PatB> bit in that direction.
>
> Well, str() was always aimed a bit at experienced S (and R)
> users, and I had always aimed somewhat to keep it's output
> "compact". I'm quite astonished that the OP didn't know about
> 1D arrays in spite of the many years he's been using R.
> Would a wierd solution like the above have helped?
>
> At the moment, I'd tend to keep it "as is" if only just for
> historical reminescence, but I can be convinced to change the
> current "tendency" ...
>
> Martin Maechler, ETH Zurich
>
What about just including "(1d-array)", something like this
> str(f)
'table' int [1:10](1d array) 5 5 9 23 26 16 9 4 2 1
- attr(*, "dimnames")=List of 1
..$ : chr [1:10] "0" "1" "2" "3" ...
>
only 9 extra characters for a rare case, and much, much less cryptic?
-- Tony Plate
>
>
> PatB> Patrick Burns patrick at burns-stat.com +44 (0)20 8525
> PatB> 0696 http://www.burns-stat.com (home of "The R
> PatB> Inferno" and "A Guide for the Unwilling S User")
> >> /Henrik
> >>
> >>
> >>> I think these days we have enough internal glue in place
> >>> that an end user would not notice the difference (but
> >>> those working at C level with R objects may need to
> >>> know).
> >>>
> >>> On Mon, 12 Jan 2009, Henrik Bengtsson wrote:
> >>>
> >>>
> >>>> Ran into the follow intermediate case in an external
> >>>> package (w/ recent R v2.8.1 patched and R v2.9.0
> >>>> devel):
> >>>>
> >>>>
> >>>>> x <- 1:2 dim(x) <- 2 dim(x)
> >>>>>
> >>>> [1] 2
> >>>>
> >>>>> x
> >>>>>
> >>>> [1] 1 2
> >>>>
> >>>>> str(x)
> >>>>>
> >>>> int [, 1:2] 1 2
> >>>>
> >>>>> nrow(x)
> >>>>>
> >>>> [1] 2
> >>>>
> >>>>> ncol(x)
> >>>>>
> >>>> [1] NA
> >>>>
> >>>>> is.vector(x)
> >>>>>
> >>>> [1] FALSE
> >>>>
> >>>>> is.matrix(x)
> >>>>>
> >>>> [1] FALSE
> >>>>
> >>>>> is.array(x)
> >>>>>
> >>>> [1] TRUE
> >>>>
> >>>>> x[1]
> >>>>>
> >>>> [1] 1
> >>>>
> >>>>> x[,1]
> >>>>>
> >>>> Error in x[, 1] : incorrect number of dimensions
> >>>>
> >>>>> x[1,]
> >>>>>
> >>>> Error in x[1, ] : incorrect number of dimensions
> >>>>
> >>>> Is str() treating single-dimension arrays incorrectly?
> >>>>
> >>>> What does it mean to have a single dimension this way?
> >>>> Should it equal a vector? I am aware of "is.vector
> >>>> returns FALSE if x has any attributes except names".
> >>>>
> >>>> /Henrik
> >>>>
> >>>> ______________________________________________
> >>>> R-devel at r-project.org mailing list
> >>>> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>>>
> >>>>
> >>> --
>
>>> Brian D. Ripley, ripley at stats.ox.ac.uk 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 at r-project.org mailing list
> >>> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>>
> >>>
> >>
>
>> ______________________________________________
>>
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> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>
> >>
> >>
>
> ______________________________________________
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>
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