⍉ Transpose r←[x]⍉y

x must be a vector of naturals, and each item must be at most the rank of y. If x is not provided, it is set to ¯1.

If x contains no duplicates, it must be a permutation of ⍳ϼy. r is the permutation of the elements of y such that for each index i, i⌷x⍉y is (x⊇i)⌷y.

If x contains duplicates, the duplicate axes only collect entries where the indices match, effectively selecting diagonals.

If x is shorter than ⍳ϼy, the remaining axes are filled with axes not mentioned.

Supports the origin extra argument, which offsets x by the origin; supports the backward extra argument, which inverts the permutation x before transposing.