[R] is this a bug (apply and class) ?

[Prof Brian Ripley]

Please do read ?apply (see the posting guide)

      If 'X' is not an array but has a dimension attribute, 'apply'
      attempts to coerce it to an array via 'as.matrix' if it is
      two-dimensional (e.g., data frames) or via 'as.array'.

and note
> sapply(esoph, class)
$agegp
[1] "ordered" "factor"

$alcgp
[1] "ordered" "factor"

$tobgp
[1] "ordered" "factor"

$ncases
[1] "numeric"

$ncontrols
[1] "numeric"


On Fri, 1 Aug 2008, David Hajage wrote:

> Hello R users,
>
> I run this code under windows XP and R 2.7.1 :
>
>> head(esoph)
>  agegp     alcgp    tobgp ncases ncontrols
> 1 25-34 0-39g/day 0-9g/day      0        40
> 2 25-34 0-39g/day    10-19      0        10
> 3 25-34 0-39g/day    20-29      0         6
> 4 25-34 0-39g/day      30+      0         5
> 5 25-34     40-79 0-9g/day      0        27
> 6 25-34     40-79    10-19      0         7
>> class(esoph$agegp)
> [1] "ordered" "factor"
>> class(esoph$alcgp)
> [1] "ordered" "factor"
>> class(esoph$tobgp)
> [1] "ordered" "factor"
>> class(esoph$ncases)
> [1] "numeric"
>> class(esoph$ncontrols)
> [1] "numeric"
>> apply(esoph, 2, class)
>      agegp       alcgp       tobgp      ncases   ncontrols
> "character" "character" "character" "character" "character"
>
> I don't understand why the result is all "character"...
>
> Thanks a lot.
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
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