Partition a list into chunks of a given size in Python

This post will discuss how to partition a list into chunks of the given length n in Python.

For example:

Input: [1, 2, 3, 4], n = 2

Output: [[1, 2], [3, 4]]

If the sequence’s length is not evenly divisible by the given length, we should fill the last partition with leftover elements.

Input: [1, 2, 3, 4, 5], n = 2

Output: [[1, 2], [3, 4], [5]]

Following are the different ways to partition a list into equal-length chunks in Python:

1. Using Slicing

A simple solution is to write a generator that yields the successive chunks of specified size from the list. This can be easily achieved with slicing, as shown below:

def partition(l, n):

for i in range(0, len(l), n):

yield l[i:i + n]

if __name__ == '__main__':

l = list(range(1, 10))

n = 3

chunks = list(partition(l, n))

print(chunks)

Download Run Code

2. Using List Comprehension

Alternatively, you can use list comprehension. This creates a new list where each list element results from some operation applied to each member.

if __name__ == '__main__':

l = list(range(1, 10))

n = 3

chunks = [l[i:i + n] for i in range(0, len(l), n)]

print(chunks)

Download Run Code

3. Using `itertools` module

Python itertools module offers the islice() function that creates a slice from the list. Here’s a generator to accomplish this:

import itertools

def partition(l, size):

for i in range(0, len(l), size):

yield list(itertools.islice(l, i, i + size))

if __name__ == '__main__':

l = list(range(1, 10))

n = 3

chunks = list(partition(l, n))

print(chunks)

Download Run Code

This can be shortened with the iter() function:

import itertools

def partition(l, size):

it = iter(l)

return iter(lambda: tuple(itertools.islice(it, size)), ())

if __name__ == '__main__':

l = list(range(1, 10))

n = 3

chunks = list(partition(l, n))

print(chunks)

Download Run Code

4. Using `toolz.itertoolz` module

Finally, you have the toolz.itertoolz module that already has the partition() function to split the sequence into tuples of a certain length.

from toolz import partition

if __name__ == '__main__':

l = list(range(1, 10))

n = 3

chunks = list(partition(n, l))

print(chunks)

Download Code

That’s all about partitioning a list into chunks of a given size in Python.

Partition a list into chunks of a given size in Python

1. Using Slicing

2. Using List Comprehension

3. Using itertools module

4. Using toolz.itertoolz module

Share this:

3. Using `itertools` module

4. Using `toolz.itertoolz` module