Flatten a nested list, Turn a nested list like [[1, 2], [3, 4]] into [1, 2, 3, 4].

Question

Anubhav Sharma · Answer

Problem Statement

Here are given a list that contains other lists inside it (one level deep). Our goal is to combine all elements into a single flat list.

Approach

There are several ways to flatten a list in Python, especially for one-level deep nested lists. Here are two common approaches:

Method 1: Using List Comprehension (Recommended)

nested_list = [[1, 2], [3, 4]]

# Flattening the list using list comprehension
flat_list = [item for sublist in nested_list for item in sublist]

print(flat_list)

Explanation:

for sublist in nested_list: Loops through each sublist, e.g., [1, 2] and [3, 4].
for item in sublist: Loops through each item inside that sublist.
item for sublist in nested_list for item in sublist: This is a nested loop inside the list comprehension.

Output:

[1, 2, 3, 4]

Method 2: Using `itertools.chain`

import itertools

nested_list = [[1, 2], [3, 4]]

flat_list = list(itertools.chain.from_iterable(nested_list))

print(flat_list)

Explanation:

itertools.chain.from_iterable() takes an iterable of iterables and flattens it.
You convert the result to a list using list().

Output:

[1, 2, 3, 4]

Use Case

This is useful when you are dealing with 2D data structures such as a grid, spreadsheet or nested data and you want a simple, one-dimensional idea.

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Flatten a nested list, Turn a nested list like [[1, 2], [3, 4]] into [1, 2, 3, 4].

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1 Answers

Problem Statement

Approach

Method 1: Using List Comprehension (Recommended)

Explanation:

Method 2: Using itertools.chain

Explanation:

Use Case

Method 2: Using `itertools.chain`