Rho ⍴
Monadic Rho means Shape
mat
1 2 3 4
5 6 7 8
9 10 11 12
⍴ mat
3 4
⍴⍴ mat
2
⍴ 'your boat'
9
⍴ 7
⍴⍴ 7
0
Dyadic Rho means Reshape
2 3 4 ⍴ 1 2 3 4 5 6 7
1 2 3 4
5 6 7 1
2 3 4 5
6 7 1 2
3 4 5 6
7 1 2 3