How to reverse array in Numpy?

Let’s learn how to reverse an array in the Numpy Python library. We will check a few methods and tricks.

Numpy Flip

The easiest way to reverse an array in Numpy is just to use the flip function.

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

reversed_array = np.flip(my_array)
print(f"This is reversed array: \n{reversed_array}")

The array just got reversed.

Numpy Flipud

However, there are other ways to reverse an array. To reverse an array in the up-down direction specifically, you can use the dedicated Numpy flipud function.

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

reverse_array_up_down = np.flipud(my_array)
print(f"Array reversed in up/down direction: \n{reverse_array_up_down}")

As shown, the array is reversed distinctly from the previous method by flipping in the up/down direction, offering utility in specific use cases.

[::-1]

With this simple Python trick, there is also the possibility to do the same without flipud.

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

flipped_array = my_array[::-1]
print(f"Array reversed in up/down direction without Numpy function: \n{flipped_array}")

The result is identical. Using my_array[::-1] effectively reverses the array in the up-down direction by creating a view, not a copy, of the array.

Numpy Fliplr

The same is possible in the left-to-right direction, of course. Fliplr is the name of a Numpy function.

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

flipped_array = np.fliplr(my_array)
print(f"Array reversed in left/right direction:  \n{flipped_array}")

The array was flipped from left to right.

Knowing all of these methods, you can flip arrays according to your needs.