Python Split list into chunks

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In this tutorial, you will learn how to split a list into chunks in Python using different ways with examples.

Python Split list into chunks

Lists are mutable and heterogenous, meaning they can be changed and contain different data types. We can access the elements of the list using their index position.

There are five various ways to split a list into chunks.

1. Using a For-Loop
2. Using the List Comprehension Method
3. Using the itertools Method
4. Using the NumPy Method
5. Using the lambda Function

Method 1: Using a For-Loop

The naive way to split a list is using the for loop with help of range() function.

The range function would read range(0, 10, 2), meaning we would loop over the items 0,2,4,6,8.

We then index our list from i:i+chunk_size, meaning the first loop would be 0:2, then 2:4, and so on.

# Split a Python List into Chunks using For Loops

sample_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
chunked_list = list()
chunk_size = 2
for i in range(0, len(sample_list), chunk_size):
    chunked_list.append(sample_list[i:i+chunk_size])
print(chunked_list)

Output

[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]

Method 2: Using the List Comprehension Method

The list comprehension is an effective way to split a list into chunks when compared to for loop, and it’s more readable.

We have asample_list and contain ten elements in it. We will split the list into equal parts with a chunk_size of 2.

# Split a Python List into Chunks using list comprehensions
sample_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
chunk_size=2
result=[sample_list[i:i + chunk_size] for i in range(0, len(sample_list), chunk_size)]
print(result)

Output

[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]

sample_list[i:i + chunk_size] give us each chunk. For example, if i=0, the items included in the chunk are i to i+chunk_size, which is from 0:2 index. In the next iteration, the items included would be 2:4 index and so on.

Method 3: Using the itertools Method

We can leverage the itertools module to split a list into chunks. The zip_longest() function returns a generator that must be iterated using for loop. It’s a straightforward implementation and returns a list of tuples, as shown below.

# Split a Python List into Chunks using itertools

from itertools import zip_longest

sample_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
chunk_size=2
result=list(zip_longest(*[iter(sample_list)]*chunk_size, fillvalue=''))
print(result)

chunked_list = [list(item) for item in list(zip_longest(*[iter(sample_list)]*chunk_size, fillvalue=''))]
print(chunked_list)

Output

[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]

Method 4: Using the NumPy Method

We can use the NumPy library to divide the list into n-sized chunks. The array_split() function splits the list into sublists of specific size defined as n.

# Split a Python List into Chunks using numpy

import numpy as np

# define array and chunk_szie
sample_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
our_array = np.array(sample_list)
chunk_size = 2

# split the array into chunks
chunked_arrays = np.array_split(our_array, len(sample_list) / chunk_size)
print(chunked_arrays)

# Covert chunked array into list
chunked_list = [list(array) for array in chunked_arrays]
print(chunked_list)

Output

[array([1, 2]), array([3, 4]), array([5, 6]), array([7, 8]), array([9, 10])]
[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]

Method 5: Using the lambda Method

We can use the lambda function to divide the list into chunks. The lambda function will iterate over the elements in the list and divide them into N-Sized chunks, as shown below.

# Split a Python List into Chunks using lambda function

sample_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
chunk_size = 2

lst= lambda sample_list, chunk_size: [sample_list[i:i+chunk_size] for i in range(0, len(sample_list), chunk_size)]
result=lst(sample_list, chunk_size)
print(result)

Output

[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]

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