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

[Robin Hankin]

Hi again everyone

I have an arbitrarily dimensional array "a" and a list "jj" of length
length(dim(a)).    The elements of jj are vectors of indexes.

How do I use do.call() to extract a[ jj[[1]], jj[[2]], jj[[3]], ...] ?


Toy example follows:

a <- matrix(1:30,5,6)
jj <- list(5:1,6:1)

I want the following

  a[ jj[[1]],jj[[2]] ]

How do I do this?



OBAttempts:

do.call("[",list(a,jj))
do.call("[",c(a,jj))
do.call("[",list(a,unlist(jj)))


Of course, the one that works is

do.call("[",list(a,jj[[1]],jj[[2]]))

but I don't know how long jj is apriori so this won't do.
-- 
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
SO14 3ZH
tel +44(0)23-8059-7743
initialDOTsurname at soc.soton.ac.uk (edit in obvious way; spam precaution)