[R] filling an array, vectorized

[Robin Hankin]

Gabor
Tamas

yet again I find myself trumped by Gabor because I forget that
TRUE is a perfectly acceptable argument to "[".

Heh.


I'll stick do.index2() in the magic package.


best wishes


rksh


On 16 Nov 2006, at 11:27, Gabor Grothendieck wrote:

> Here is minor simplification:
>
> do.index2 <- function(a,f){
>  jj <- function(i) seq(dim(a)[i])
>  index <- as.matrix(expand.grid(lapply(jj(TRUE), jj)))
>  a[index] <- apply(index, 1, f)
>  a
> }
>
> # test
> a <- array(0,c(2,3,4))
> identical(do.index(a, f), do.index2(a, f))
> b <- array(0,c(2,2,2,2))
> identical(do.index(b, f), do.index2(b, f))
>
>
> On 11/16/06, Robin Hankin <r.hankin at noc.soton.ac.uk> wrote:
>> Tamas
>>
>> first of all, Thank You for a really well-posed, interesting problem.
>> Answer follows.
>>
>>
>>
>> do.index <- function(a,f){
>>   jj <- function(i){seq_len(dim(a)[i])}
>>   index <- as.matrix(expand.grid(sapply(1:length(dim
>> (a)),jj,simplify=FALSE)))
>>   a[index] <- apply(index,1,f)
>>   return(a)
>> }
>>
>>
>>
>> f <- function(l){
>>   sum(unlist(l))
>> }
>>
>> a <- array(0,c(2,3,4))
>> b <- array(0,c(2,2,2,2))
>>
>> do.index(a,f)
>> do.index(b,f)
>>
>>
>>
>> best wishes
>>
>> Robin
>>
>>
>>
>>
>>
>> On 15 Nov 2006, at 19:16, Tamas K Papp wrote:
>>
>> > Hi,
>> >
>> > I am sure this has come up before, but my searches of the archive
>> > didn't give any results (maybe I didn't use the right keywords,  
>> but if
>> > I use too many, the search times out).
>> >
>> > I have a vector of dimensions n, length is not fixed, eg
>> >
>> > n <- c(4,5,7)
>> >
>> > or
>> >
>> > n <- c(19,4,5,7)
>> >
>> > and a function f that takes a vector of indices, same length of  
>> n, and
>> > gives a scalar.
>> >
>> > I would like to fill the array
>> >
>> > a <- array(dim=n)
>> >
>> > so that (... is just notation, not R's ...)
>> >
>> > a[i,j,k,...] <- f(list(i,j,k,...))
>> >
>> > I would use loops, but since n can have different lengths, I don't
>> > know how many loops I would need beforehand.  Is there a way to do
>> > this?
>> >
>> > Thanks,
>> >
>> > Tamas
>> >
>> > ______________________________________________
>> > R-help at stat.math.ethz.ch 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.
>>
>>

--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743