On May 28, 2009, at 11:25 AM, eric lee wrote:
Hi,
I'm running R 2.7.2 on windows XP. I'd like to find the maximum of a
3-d array over it's third index to create a 2-d array. For example:
x <- array(c(1,2,3,10,11,12,3:8),c(2,3,2))
x
, , 1
[,1] [,2] [,3]
[1,] 1 3 11
[2,] 2 10 12
, , 2
[,1] [,2] [,3]
[1,] 3 5 7
[2,] 4 6 8
x1 <- x[,,1]
x2 <- x[,,2]
pmax(x1,x2)
[,1] [,2] [,3]
[1,] 3 5 11
[2,] 4 10 12
Consider:
> apply(x, 1:2, max)
[,1] [,2] [,3]
[1,] 3 5 11
[2,] 4 10 12
or
> apply(x, c(1,2), max) # not necessarily adjacent dimensions
[,1] [,2] [,3]
[1,] 3 5 11
[2,] 4 10 12
Is there a pre-defined function that I can use to do this without
using a for-loop? Also, the third index can be long and of variable
length, so I don't want to explicitly write out x1, x2,... Thanks in
advance for your help.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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