September 11, 2024

Python Tutorials

Flatten a List in Python

Flattening a list in Python means converting a nested list (a list of lists) into a single, one-dimensional list. This operation is common when dealing with data structures that include multiple levels of nesting. Below are different methods to achieve this in Python.

1. Using List Comprehension

List comprehension is a concise way to flatten a list by iterating over the sublists and collecting their elements into a new list.

# Example nested list
nested_list = [[1, 2, 3], [4, 5], [6, 7, 8]]

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

print(flattened_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8]

2. Using a Recursive Function

A recursive function can handle arbitrarily nested lists by flattening each sublist as it encounters them.

# Recursive function to flatten a list
def flatten_list(nested_list):
    flattened = []
    for item in nested_list:
        if isinstance(item, list):
            flattened.extend(flatten_list(item))
        else:
            flattened.append(item)
    return flattened

# Example nested list
nested_list = [1, [2, [3, 4], 5], [6, 7], 8]

# Flattening using the recursive function
flattened_list = flatten_list(nested_list)

print(flattened_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8]

3. Using itertools.chain

The itertools.chain function can be used to flatten a list by chaining multiple iterables together.

# Importing chain from itertools
from itertools import chain

# Example nested list
nested_list = [[1, 2, 3], [4, 5], [6, 7, 8]]

# Flattening using itertools.chain
flattened_list = list(chain.from_iterable(nested_list))

print(flattened_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8]

4. Using NumPy (for Numerical Data)

If you are working with numerical data, NumPy provides a convenient way to flatten arrays.

# Importing NumPy
import numpy as np

# Example nested list
nested_list = [[1, 2, 3], [4, 5], [6, 7, 8]]

# Converting nested list to a NumPy array and flattening
flattened_array = np.array(nested_list).flatten()

print(flattened_array)  # Output: [1 2 3 4 5 6 7 8]

Conclusion

Flattening a list in Python can be accomplished using various methods depending on your specific needs and the complexity of the nesting. Whether you choose list comprehension, a recursive approach, or tools from libraries like itertools or numpy, each method has its own advantages and use cases.

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