[Rd] RFC: sapply() limitation from vector to matrix, but not further

[Tony Plate]

The abind() function from the abind package is an alternative here -- it can take a list argument, which makes it easy to use with the result of lapply().  It's also able take direction about which dimension to join on.

 > x <- list(a=1,b=2,c=3)
 > f <- function(v) matrix(v, nrow=2, ncol=4)
 > sapply(x, f)
      a b c
[1,] 1 2 3
[2,] 1 2 3
[3,] 1 2 3
[4,] 1 2 3
[5,] 1 2 3
[6,] 1 2 3
[7,] 1 2 3
[8,] 1 2 3
 >
 > # The 'along=' argument to abind() determines on which dimension
 > # the list elements are joined.  Use a fractional value to put the new
 > # dimension between existing ones.
 >
 > dim(abind(lapply(x, f), along=0))
[1] 3 2 4
 > dim(abind(lapply(x, f), along=1.5))
[1] 2 3 4
 > dim(abind(lapply(x, f), along=3))
[1] 2 4 3
 > abind(lapply(x, f), along=3)
, , a

      [,1] [,2] [,3] [,4]
[1,]    1    1    1    1
[2,]    1    1    1    1

, , b

      [,1] [,2] [,3] [,4]
[1,]    2    2    2    2
[2,]    2    2    2    2

, , c

      [,1] [,2] [,3] [,4]
[1,]    3    3    3    3
[2,]    3    3    3    3

 >

On 12/28/2010 8:49 AM, Martin Maechler wrote:
>>>>>> Gabor Grothendieck<ggrothendieck at gmail.com>
>>>>>>      on Mon, 27 Dec 2010 17:06:25 -0500 writes:
>      >  On Wed, Dec 1, 2010 at 3:39 AM, Martin Maechler
>      >  <maechler at stat.math.ethz.ch>  wrote:
>      >>  My proposal -- implemented and "make check" tested -- is
>      >>  to add an optional argument  'ARRAY' which allows
>      >>
>      >>>  sapply(v, myF, y = 2*(1:5), ARRAY=TRUE)
>
>      >  It would reduce the proliferation of arguments if the
>      >  simplify= argument were extended to allow this,
>      >  e.g. simplify = "array" or perhaps simplify = n would
>      >  allow a maximum of n dimensions.
>
> That's a good idea, though it makes the
> implementation/documentation very slightly more complicated.
>
> I'm interested to get more feedback on my other questions,
> notably the only about *changing*  vapply() (on the C-level) to
> behave "logical" in the sense of adding one  dim(.)ension in
> those cases, the FUN.VALUE (result prototype) has a dim().
>
>
> Martin
>
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