[R] do.call("+", ...)

[Robin Hankin]

Hello everyone

thanks for the replies.  My application (predictably) involves
arbitrary dimensioned arrays, so I will need to generalize
the suggestions slightly (except Peter Dalgaard's, which
works out-of-the-box).

At least I wasn't missing anything obvious about do.call().

Why is Peter Dalgaard's suggestion necessary?  Why can't  "+"
take more than two arguments?






On 17 Nov 2006, at 10:38, Peter Dalgaard wrote:

> rfrancois at mango-solutions.com writes:
>
>> Hi,
>>
>> You could stack your list in an array and then use apply :
>>
>> myArray <- array( unlist(lapply(1:3, f) ) , dim =c(2, 3, 3))
>> apply(myArray, c(1,2), sum)
>
> Or fixup "+" to take more than two arguments, e.g.
>
> "++" <- function(x, ...) if (nargs() == 1) x else x + Recall(...)
>
> f  <- function(i){matrix((1:6)^i, 2, 3)}
> do.call("++", sapply(1:4, f, simplify=FALSE))
>
> ##
>
>> "++" <- function(x, ...) if (nargs() == 1) x else x + Recall(...)
>> f  <- function(i){matrix((1:6)^i, 2, 3)}
>> do.call("++", sapply(1:4, f, simplify=FALSE))
>      [,1] [,2] [,3]
> [1,]    4  120  780
> [2,]   30  340 1554
>
>
>
>
>> Cheers,
>>
>> Romain
>>
>> Quoting Robin Hankin <r.hankin at noc.soton.ac.uk>:
>>
>>> Hi
>>>
>>> How do I make do.call() take "+" as a function for a list of more
>>> than two elements?
>>>
>>> Toy problem follows:
>>>
>>>
>>> f  <- function(i){matrix((1:6)^i,2,3)}
>>>
>>> # Thus f() returns a matrix of size 2x3; I want to add a whole bunch
>>> of such matrices,
>>> # as in  f(1) + f(2) + f(3) + f(4)
>>>
>>> # But:
>>>
>>>
>>>
>>>> do.call("+",sapply(1:4,f,simplify=FALSE))
>>> Error in do.call("+", sapply(1:4, f, simplify = FALSE)) :
>>> 	operator needs one or two arguments
>>>
>>>
>>>
>>>
>>> Also,
>>>
>>>
>>>> do.call(sum,sapply(1:4,f,simplify=FALSE))
>>> [1] 2828
>>>
>>>
>>> doesn't do what I want (I would like a 2x3 matrix whose elements  
>>> are the
>>> sum of corresponding elements in my list)
>>>
>>> How to do this nicely?
>>>
>>>
> ucible code.

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