, — Ravel / Catenate

Function. Ranks: ∞ monadic, ∞ ∞ dyadic

,Y makes a vector of the items. With axes, ,⍠K Y ravels consecutive axes and ,⍠⍬ Y appends an axis of length 1.

,[1 2⋄3 4]       ⍝ 1 2 3 4
⍴,7                ⍝ [1]ₓ
⍴,⍠1 2 (2 3 4⍴⍳24) ⍝ [2 12]ₓ

X,Y joins on the last axis. X,⍠K Y joins on axis K. Other axes agree, with unit and adjacent-rank extension.

1 2,3 4            ⍝ 1 2 3 4

There is no laminate. [x⋄y] has x and y as its major cells, along a new leading axis. x,⍤0 y pairs the items of x and y along a new last axis.

x←1 2 ⋄ y←3 4
[x⋄y]            ⍝ [1 2⋄3 4]
x,⍤0 y             ⍝ [1 3⋄2 4]

Inverse

,⁻¹Y gives back Y when it’s a vector. X,⁻¹Y removes the fixed X from the front of Y. With the right argument fixed, (,↢X)⁻¹Y removes it from the end.

,⁻¹1 2 3           ⍝ 1 2 3
1 2,⁻¹1 2 3 4      ⍝ 3 4
(,↢3 4)⁻¹1 2 3 4   ⍝ 1 2