Monadic Comma Bar means
⍪ 2 3 4
2
3
4
cube ⍝ 3D array
1 2
3 4
5 6
7 8
⍪ cube
1 2 3 4
5 6 7 8
Dyadic Comma Bar means
mat
1 2 3
4 5 6
mat ⍪ 0
1 2 3
4 5 6
0 0 0
mat ⍪ 7 8 9
1 2 3
4 5 6
7 8 9
⍪ 2 3 4
2
3
4
cube ⍝ 3D array
1 2
3 4
5 6
7 8
⍪ cube
1 2 3 4
5 6 7 8
mat
1 2 3
4 5 6
mat ⍪ 0
1 2 3
4 5 6
0 0 0
mat ⍪ 7 8 9
1 2 3
4 5 6
7 8 9