5 Best Ways to Return the Element-wise Square of an Array Input in Python

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πŸ’‘ Problem Formulation: When working with numerical data in Python, a common requirement is to calculate the square of each element in an array or a list. Suppose you have an input array [1, 2, 3, 4], and you want to produce an output that squares each element, resulting in [1, 4, 9, 16]. Below are five effective methods to achieve this in Python.

Method 1: Using a For Loop

The most basic method to square each element in a Python array is to iterate through the array with a for loop and square each element. This method is intuitive and easy to implement for beginners.

Here’s an example:

input_array = [1, 2, 3, 4]
squared_array = []
for number in input_array:
    squared_array.append(number ** 2)

Output: [1, 4, 9, 16]

This code snippet initializes an empty list squared_array, then iterates over each number in input_array, appending the square of the number to the squared_array. The ** operator in Python is used to raise a number to the power of 2, effectively squaring it.

Method 2: Using List Comprehension

List comprehension offers a more concise and idiomatic way to create a new list by applying an expression to each item in the existing list. It’s often more readable and compact than a for loop.

Here’s an example:

input_array = [1, 2, 3, 4]
squared_array = [number ** 2 for number in input_array]

Output: [1, 4, 9, 16]

The list comprehension [number ** 2 for number in input_array] is a short way to create a new list where each element is the result of the square of the corresponding element from input_array.

Method 3: Using the map() Function

The map() function applies a given function to each item of an iterable and returns a map object. It can be used to perform operations on array elements efficiently and with less code.

Here’s an example:

input_array = [1, 2, 3, 4]
squared_array = list(map(lambda x: x ** 2, input_array))

Output: [1, 4, 9, 16]

We use map() along with a lambda function to apply the square operation to each element in input_array. The result is then converted into a list to get the squared elements as a list.

Method 4: Using NumPy

NumPy is a powerful library for numerical processing in Python. It provides a highly efficient array structure and operations that can perform element-wise calculations, like squaring, much faster than the regular Python lists.

Here’s an example:

import numpy as np
input_array = np.array([1, 2, 3, 4])
squared_array = np.square(input_array)

Output: array([ 1, 4, 9, 16])

In this code snippet, np.array() is used to create a NumPy array. Then, the np.square() function directly computes the squares of all elements in the array, returning a new NumPy array containing the squared values.

Bonus One-Liner Method 5: Using a Generator Expression with tuple()

A generator expression is similar to list comprehension, but instead of creating a list, it generates items on the fly, which can be more memory efficient for large arrays. By passing the generator expression to the tuple() function, you get an immutable tuple of squared values.

Here’s an example:

input_array = [1, 2, 3, 4]
squared_array = tuple(number ** 2 for number in input_array)

Output: (1, 4, 9, 16)

The generator expression is used inside the tuple() call, which computes and returns the squared values as a tuple, preserving memory by avoiding the creation of an intermediate list.


  • Method 1: For Loop. Easy for beginners to understand. Not very Pythonic. Less efficient for larger arrays.
  • Method 2: List Comprehension. Pythonic and concise. Better performance than a for loop. Still not the most efficient for very large arrays.
  • Method 3: Map Function. Compact code. Can be less intuitive for those not familiar with functional programming. Requires cast to list.
  • Method 4: Using NumPy. Highly efficient for large arrays. Requires NumPy installation. Overkill for small tasks.
  • Method 5: Generator with tuple(). Memory efficient for huge arrays. Returns an immutable tuple. Not suitable when a list is needed.