How to split a list into sublists python

def split(list_a, chunk_size): for i in range(0, len(list_a), chunk_size): yield list_a[i:i + chunk_size] chunk_size = 2 my_list = [1,2,3,4,5,6,7,8,9] print(list(split(my_list, chunk_size)))

Output

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

In the above example, we have defined a function to split the list.

• Using a for loop and range() method, iterate from 0 to the length of the list with the size of chunk as the step.
• Return the chunks using yield. list_a[i:i+chunk_size] gives each chunk. For example, when i = 0, the items included in the chunk are i to i + chunk_size which is 0 to (0 + 2)th index. In the next iteration, the items included are 2 to 2 + 2 = 4.

Learn more about yield at Python Generators.

You can do the same thing using list compression as below.

chunk_size = 2 list_chunked = [my_list[i:i + chunk_size] for i in range(0, len(my_list), chunk_size)] print(list_chunked)

Output

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

Learn more about list comprehension at Python List Comprehension.

Example 2: Using numpy

import numpy as np my_list = [1,2,3,4,5,6,7,8,9] print(np.array_split(my_list, 5))

Output

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

array_split() is a numpy method that splits a list into equal sized chunks. Here, the size of the chunk is 5.

Note: You need to install numpy on your system.

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

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 a sample_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]]