Invert Elements of Boolean Arrays

Inverting The Elements Of A Boolean Array In Python

Boolean arrays – they contain only True and False, yet these limited values hide immense power. With boolean arrays, you can represent complex logic, filter huge datasets, model neural networks, and much more. In Python, boolean arrays are injected with steroids thanks to NumPy, a library that exploits their full potential. 

In this action-packed tutorial, we’ll explore how to invert all the values in an array, swapping True for False and False for True. By the end, you will have learned a simple way to manipulate boolean arrays, enabling more complex logic in your datasets, filters, and models. Boolean arrays, combined with NumPy’s functions, provide a powerful toolset for data analysis and machine learning in Python.

What is a Boolean Array in Python?

A boolean array is an array that has boolean values like True or False or maybe 1 or 0. It can be formed by using dtype = bool. Everything is considered true except for 0, None, False or empty strings. In Python, these arrays are implemented using the NumPy library

NumPy is a library for scientific computing in Python. It supports large, multi-dimensional arrays and matrices, along with a large collection of high-level mathematical functions to operate on these arrays.

To define a Boolean array in NumPy, we use the np.array() function and pass in a list of Boolean values. For example:

import numpy as np

arr_bool = np.array([1, 1.1, 0, None, 'a', '', True, False], dtype=bool)


[ True  True False False  True False  True False]

Some useful operations we can perform on Boolean arrays are:

  • Logical operations: And (&), Or (|) and Not (~) using np.logical_and(), np.logical_or() and np.logical_not() respectively.
  • Count true values: Use np.count_nonzero(bool_arr)
  • Find position of true values: Use np.where(bool_arr) 
  • Comparison operations: ==, !=, >, <, >=, <=. These return new Boolean arrays.

This can also be an input array instead of a pre-defined array.

Also read: Python Course – Bit-wise Operators

Methods for inverting elements of Boolean Arrays

Following are the methods you can apply for inverting the elements of a boolean array in Python.

1. Using the np.invert() function

The simplest and most straightforward method is to use NumPy’s built-in np.invert() function. This will directly invert all the elements of the Boolean array. NumPy is a library for scientific computing in Python, and provides functions to operate on large data arrays.

import numpy as np
arr = np.array((True, True, False, True, False))
arr_inver = np.invert(arr)


[False False  True False  True]

This creates a Boolean array arr and then uses np.invert() to invert all the elements, storing the result in arr_invert.

2. Using the if-else method

We can also write an if-else statement to check each element of the array and invert it manually. This requires iterating over each element in the array, and checking if the element is True or False. If True, we make it False and vice versa.

arr = [True, False, True, False]
result = []

for elem in arr:
    if elem:

# [False, True, False, True]


[1, 0, 1, 0]

This iterates over each element elem in the input array arr. For each element, an if-else statement checks the value:

  • If elem is True, we append False to the result.
  • Else, if elem is False, we append True.

This has the effect of inverting all the values in the array, building up the inverted result in the result array.

While this method works, it is slower than using NumPy’s np.invert() function. This is because NumPy is optimized to perform vectorized operations on arrays, rather than iterating over elements one by one.


In this article, we explored two methods to invert the elements of a Boolean array in Python. The simplest approach is to use the np.invert() function from NumPy, which directly inverts all the elements of the array. However, we can also write an iterative if-else statement to check and invert each element individually. 

While the if-else method works, NumPy’s vectorized operations are optimized for speed and performance on large data arrays. Therefore, np.invert() is the recommended approach for inverting Boolean arrays whenever possible.

Boolean arrays have many applications in data analysis and scientific computing. Together with NumPy, they provide a powerful toolset for efficiently manipulating and analyzing data in Python.

In summary, NumPy’s np.invert() function is the fastest and most Pythonic way to invert the elements of a Boolean array. I hope this article helped strengthen your understanding of Boolean arrays and NumPy in Python!