Most efficient way to reverse a numpy array

Question

Believe it or not, after profiling my current code, the repetitive operation of numpy array reversion ate a giant chunk of the running time. What I have right now is the com

Answer 1

Expanding on what others have said I will give a short example.

If you have a 1D array ...

>>> import numpy as np
>>> x = np.arange(4) # array([0, 1, 2, 3])
>>> x[::-1] # returns a view
Out[1]: 
array([3, 2, 1, 0])

But if you are working with a 2D array ...

>>> x = np.arange(10).reshape(2, 5)
>>> x
Out[2]:
array([[0, 1, 2, 3, 4],
       [5, 6, 7, 8, 9]])

>>> x[::-1] # returns a view:
Out[3]: array([[5, 6, 7, 8, 9],
               [0, 1, 2, 3, 4]])

This does not actually reverse the Matrix.

Should use np.flip to actually reverse the elements

>>> np.flip(x)
Out[4]: array([[9, 8, 7, 6, 5],
               [4, 3, 2, 1, 0]])

If you want to print the elements of a matrix one-by-one use flat along with flip

>>> for el in np.flip(x).flat:
>>>     print(el, end = ' ')
9 8 7 6 5 4 3 2 1 0