Hello Juhana
try this (but there must be a better way!)
stratified.select <- function(A,J){
out <- sapply(J,function(i){sample(A[,,i],1)})
attributes(out) <- attributes(J)
return(out)
}
A <- array(letters[1:12],c(2,2,3))
J <- matrix(c(1,2,3,3),2,2)
R> stratified.select(A,J)
[,1] [,2]
[1,] "b" "i"
[2,] "g" "k"
R> stratified.select(A,J)
[,1] [,2]
[1,] "d" "j"
[2,] "f" "l"
R>
best wishes
Robin
On Apr 26, 2005, at 05:16 am, juhana vartiainen wrote:
Hi all
Suppose I have a dim=c(2,2,3) matrix A, say:
A[,,1]=
a b
c d
A[,,2]=
e f
g h
A[,,3]=
i j
k l
Suppose that I want to create a 2x2 matrix X, which picks elements
from the above-mentioned submatrices according to an index matrix J
referring to the "depth" dimension:
J=
1 3
2 3
In other words, I want X to be
X=
a j
g l
since the matrix J says that the (1,1)-element should be picked from
A[,,1], the (1,2)-element should be picked from A[,,3], etc.
I have A and I have J. Is there an expression in A and J that creates
X?
Thanks
Juhana
[EMAIL PROTECTED]
--
Juhana Vartiainen
docent in economics
Director, FIEF (Trade Union Foundation for Economic Research,
Stockholm), http://www.fief.se
gsm +46 70 360 9915
office +46 8 696 9915
email [EMAIL PROTECTED]
homepage http://www.fief.se/staff/Juhana/index.html
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--
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
European Way, Southampton SO14 3ZH, UK
tel 023-8059-7743
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