# [R] transposing/rotating XY in a 3D array

andzsin andzsinszan at gmail.com
Fri May 15 09:08:06 CEST 2009

```Dear list,

We have a number of files containing similarly structured data:
file1:
A B C
1 2 3
4 5 6

file2:
A B C
7 8 9
10 11 12
... etc

My part of R receives all these data as an array: 1,2,3... 12 together
with info about dimensions (row,col,fileN) . (

Converting the data into 3D cannot simply done by:
array(x, c(2,3,2))
because breaks the structure (e.g. 1,3,5 is type mismatch)

array(1:12,c(2,3,2))
, , 1

[,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6
...

Of course  following R's indexing order (rowIndex is the fastest)
retains the structures, but X and Y dimensions are transposed. (note, c
(2,3,2) => (3,2,2))

array(1:12, c(3,2,2))
, , 1

[,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6

Its like converting into Japanese vertical reading.
It is not that I cannot get used to it, but I guess it is less error
prone if I have the same order as in the data files.

Now I am using an ad-hoc function (see below) to transpose back the
rotated YX into a  XYZ array, but I'd rather go with built-ins, e.g.
byrow=T, or t()  -- and also without duplicating my data.

Gabor

<code>
transposeXYinXYZ<-function(x){
y <- array(NA,c(dim(x),dim(x),dim(x)))

for(i in 1:dim(x)){
y[,,i] <- t(x[,,i])
}
return (y)
}
xyz <- array(1:24,c(4,3,2))
yxz <- transpose(x)

xyz
yxz
</code>

```