R help - Nov 2008 - Outer, kronecker, etc.

`outer` (and related functions like kronecker) require that their
functional argument operate elementwise on arrays.  This means for
example that

     outer( 1:2, 3:4, list)

or

     outer(1:2,3:4,function(a,b){1})

gives an error.

Is there a version of `outer`/`kronecker`/etc. that takes arbitrary
functions and does its own elementwise mapping?  In the first example
above, I'd expect the result to be the same as

    mm <- matrix(list(list(1,3),list(1,4),list(2,3),list(2,4)),2,2)

which prints as

     [,1]   [,2]
[1,] List,2 List,2
[2,] List,2 List,2

By the way: how can I get this not to abbeviate the entries but
instead give me something like:

     [,1]       [,2]
[1,] list(1, 3) list(2, 3)
[2,] list(1, 4) list(2, 4)

The closest I can get is matrix(as.character(mm),2,2)

By-the-way^2: is there some Xapply function that maps a function over
all the elements of a structure (vector, matrix, list, ...) and
preserves the original structure?  For example, I'd want
Xapply(matrix(1:4^2,2,2),sqrt) == sqrt(matrix(1:4^2,2,2)).  In this
case, I'd use Xapply(as.character,mm), because as.character returns a
vector.

Thanks,

         -s

See ?Vectorize.

sqrt() works on a matrix, and so does

A <- matrix(1:4^2,2,2)
A[] <- sapply(A, sqrt)

On Wed, 12 Nov 2008, Stavros Macrakis wrote:
> `outer` (and related functions like kronecker) require that their
> functional argument operate elementwise on arrays.  This means for
> example that
>
>     outer( 1:2, 3:4, list)
>
> or
>
>     outer(1:2,3:4,function(a,b){1})
>
> gives an error.
>
> Is there a version of `outer`/`kronecker`/etc. that takes arbitrary
> functions and does its own elementwise mapping?  In the first example
> above, I'd expect the result to be the same as
>
>    mm <- matrix(list(list(1,3),list(1,4),list(2,3),list(2,4)),2,2)
>
> which prints as
>
>     [,1]   [,2]
> [1,] List,2 List,2
> [2,] List,2 List,2
>
> By the way: how can I get this not to abbeviate the entries but
> instead give me something like:
>
>     [,1]       [,2]
> [1,] list(1, 3) list(2, 3)
> [2,] list(1, 4) list(2, 4)
Write your own print function.  It does not 'abbeviate the entries': it 
prints a summary of them.
> The closest I can get is matrix(as.character(mm),2,2)
mm[] <- sapply(mm, deparse)
> By-the-way^2: is there some Xapply function that maps a function over
> all the elements of a structure (vector, matrix, list, ...) and
> preserves the original structure?  For example, I'd want
> Xapply(matrix(1:4^2,2,2),sqrt) == sqrt(matrix(1:4^2,2,2)).  In this
> case, I'd use Xapply(as.character,mm), because as.character returns a
> vector.
>
> Thanks,
>
>         -s
>
> ______________________________________________
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> 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

you may want to look into Hadley's new package plyr for this kind of  
operation.

baptiste

On 12 Nov 2008, at 17:51, Stavros Macrakis wrote:
> By-the-way^2: is there some Xapply function that maps a function over
> all the elements of a structure (vector, matrix, list, ...) and
> preserves the original structure?  For example, I'd want
> Xapply(matrix(1:4^2,2,2),sqrt) == sqrt(matrix(1:4^2,2,2)).  In this
> case, I'd use Xapply(as.character,mm), because as.character returns a
> vector.
_____________________________

Baptiste Augui?

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag