X must be a scalar or vector of depth ≤2 of integers each ≥⎕IO. Y may be any array. In general, the result R is similar to that obtained by square-bracket indexing in that:

      (I J ... ⌷ Y) ≡ Y[I;J;...]

The length of left argument X must be less than or equal to the rank of right argument Y. Any missing trailing items of X default to the index vector of the corresponding axis of Y.

Note that in common with square-bracket indexing, items of the left argument X may be of any rank and that the shape of the result is the concatenation of the shapes of the items of the left argument:

      (⍴X⌷Y) ≡ ↑,/⍴¨X

Index is sometimes referred to as squad indexing.

Note that index may be used with selective specification.

⎕IO is an implicit argument of index.

      ⎕IO←1
 
      VEC←111 222 333 444
      3⌷VEC
333
      (⊂4 3)⌷VEC
444 333
      (⊂2 3⍴3 1 4 1 2 3)⌷VEC
333 111 444
111 222 333
 
      ⎕←MAT←10⊥¨⍳3 4
11 12 13 14
21 22 23 24
31 32 33 34
 
      2 1⌷MAT
21
      2⌷MAT
21 22 23 24

 
      3(2 1)⌷MAT
32 31
      (2 3)1⌷MAT
21 31
      (2 3)(,1)⌷MAT
21
31
      ⍴(2 1⍴1)(3 4⍴2)⌷MAT
2 1 3 4
      ⍴⍬ ⍬⌷MAT
0 0
      (3(2 1)⌷MAT)←0 ⋄ MAT    ⍝ Selective assignment.
11 12 13 14
21 22 23 24
 0  0 33 34

Indexing Classes

If Y is a ref to an instance of a Class with a Default property, ⌷ is applied to the Default property. Similarly, ⌷ applied to a COM or .NET collection returns the appropriate item(s) of the collection.

Example

      ↑⎕SRC c
:Class c                 
    :Property Default p  
    :Access Public Shared
        ∇ r←get          
          r←2 3 4⍴⎕A     
        ∇                
    :EndProperty         
:EndClass                

      2⌷c
MNOP
QRST
UVWX