How to reverse array in Numpy?

Posted on By Pythoneo

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

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}")

Numpy how to reverse array

The array just got reversed.

Numpy Flipud

However, there are other ways to reverse an array. This is how you reverse an array in the up-down direction. There is a dedicated Numpy flipud function for that.

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}")

Numpy reverse array up down direction

As you can see, the array just got reversed and looks way different than the previous flip. This flipped array worked in an up/down direction, which can be useful in some use cases.

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[::-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}")

Python reverse array up down direction

As you can see, the result is the same. my_array [::-1] simply created an array view in the up-down direction, as expected.

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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}")

Numpy reverse array left right direction

The array was flipped from left to right.

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

Key Takeaways

  • There are three ways to reverse an array in Numpy:
  • Using the `flip()` function
  • Using the `flipud()` function
  • Using the `[::-1]` slicing syntax
  • The `flip()` function reverses the array in both the up-down and left-right directions.
  • The `flipud()` function only reverses the array in the up-down direction.
  • The `[::-1]` slicing syntax reverses the array in the left-right direction.
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    FAQ

    • Q: Which method is the best to reverse an array?
    • A: The best method to use depends on your specific needs. If you need to reverse the array in both directions, then the `flip()` function is the best option. If you only need to reverse the array in one direction, then the `flipud()` or `[::-1]` slicing syntax can be used.
    • Q: How do I reverse an array in a specific direction?
    • To reverse an array in a specific direction, you can use the `flip()` function and specify the axis that you want to reverse.
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