Reshape, Join & Split

reshape() rearranges the same elements into a new shape:

arr = np.arange(1, 13) # 12 elements arr.reshape(4, 3) # 4 rows × 3 columns arr.reshape(2, 3, 2) # 3-D

The total number of elements must stay the same: 12 elements fit 4×3, 2×6, or 2×3×2, but not 5×3.

reshape usually returns a view of the original data, so it's fast even for huge arrays.