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Y may be any array.  R is an array of shape ⌽⍴Y, similar to Y with the order of the axes reversed.

Examples

      M
1 2 3
4 5 6
 
      ⍉M
1 4
2 5
3 6

      cube    ⍝ 3D array
 1  2  3  4
 5  6  7  8
 9 10 11 12
           
13 14 15 16
17 18 19 20
21 22 23 24

      ⍉ cube
 1 13
 5 17
 9 21
     
 2 14
 6 18
10 22
     
 3 15
 7 19
11 23
     
 4 16
 8 20
12 24

      ⍴ cube
2 3 4
      ⍴ ⍉ cube    ⍝ transpose reverses shape
4 3 2