How to apply a function to each matrix in a 3D array¶

Use rank 2 to treat each matrix (2-cell) of a rank-3 array as an independent operand:

      A ← 2 3 4⍴⍳24
      (⌽⍤2) A

This reverses the rows within each of the two matrices.

      (+/⍤2) A

This sums each row of each matrix, reducing the last axis.

      (⍉⍤2) A

This transposes each matrix independently.

The frame shape is 2 (the leading axis) and the cell shape is 3 4 (each matrix).