, — Ravel / Catenate,Y makes a vector of the items. ,[K]Y ravels consecutive axes; ,[]Y appends a unit axis.
,2 2⍴⍳4 ⍝ 1 2 3 4
⍴,7 ⍝ ,1x
X,Y joins on the last axis. X,[K]Y joins on axis K. Other axes agree, with scalar and adjacent-rank extension.
1 2,3 4 ⍝ 1 2 3 4
Fractional axes laminate: insert a new axis.
⍴1 2,[0.5]3 4 ⍝ 2x 2x