X is a scalar or vector of indices of Y.
R is an item selected from the structure of Y according to X.
Elements of X select from successively deeper levels in the structure of Y. The items of X are simple integer scalars or vectors which identify a set of indices, one per axis at the particular level of nesting of Y in row-major order. Simple scalar items in Y may be picked by empty vector items in X to any arbitrary depth.
⎕IO is an implicit argument of Pick.
G←('ABC' 1)('DEF' 2)('GHI' 3)('JKL' 4)
G←2 3⍴G,('MNO' 5)('PQR' 6)
G
ABC 1 DEF 2 GHI 3
JKL 4 MNO 5 PQR 6
((⊂2 1),1)⊃G JKL (⊂2 1)⊃G JKL 4 ((2 1)1 2)⊃G K (5⍴⊂⍳0)⊃10 10