CODEWITHSUNDEEP
arraysrsimulationsubset
Bajcz
Bajcz

Reputation: 472

How do I smartly subset an array in R with dynamic dimensions?

I'm crafting a simulation model, and I think this problem has an easy fix, but I'm just not that used to working with arrays. Let's say I have an array, Array1, that has 3 dimensions. The first two are of constant and equal length, L, but the third dimension can be of length from 1 to X at any given time.

I want to be able to periodically subset Array1 to create a second array, Array2, that is composed of up to the last Y "sheets" of Array1. In other words, if the length of the third dimension of Array1 is greater than Y, then I want just the last Y sheets of Array1 but, if it's less than Y, I want all sheets of Array1.

I know that I can crudely pull this off using the tail function and a little finagling:

tmp1 = tail(Array1, (L*L*Y))
Array2 = array(tmp1, dim = (L, L, (L*L/length(tmp1))))

But it seems like there could be a more elegant way of doing this. Is there an equivalent of tail for arrays in R? Or is there a way that Array2 could be produced via simple logical indexing of Array1? Or perhaps the apply function could be used somehow?

Upvotes: 0

Views: 267

Answers (1)

Hong Ooi
Hong Ooi

Reputation: 57686

Were you after something like this?

a <- array(1:(3*4*5), dim=c(3,4,5))
x <- dim(a)[3]
y <- 2
a[, , seq(to=x, len=min(x, y))]

, , 1

     [,1] [,2] [,3] [,4]
[1,]   37   40   43   46
[2,]   38   41   44   47
[3,]   39   42   45   48

, , 2

     [,1] [,2] [,3] [,4]
[1,]   49   52   55   58
[2,]   50   53   56   59
[3,]   51   54   57   60

Upvotes: 1

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