Table of Contents
In this example, you will learn to make a flattened list from a nested list in Python.
To understand this example, you should have the knowledge of the following Python programming topics:
1. Example 1: Using List Comprehension
my_list = [[1], [2, 3], [4, 5, 6, 7]] flat_list = [num for sublist in my_list for num in sublist] print(flat_list)
Output
[1, 2, 3, 4, 5, 6, 7]
This is one of the simplest pythonic ways of flattening a list.
- Using list comprehension access the sublist from
my_list
, then access each element of the sublist. - Each element num is stored in
flat_list
.
Learn more about list comprehension at Python List Comprehension.
2. Example 2: Using Nested for Loops (non pythonic way)
my_list = [[1], [2, 3], [4, 5, 6, 7]] flat_list = [] for sublist in my_list: for num in sublist: flat_list.append(num) print(flat_list)
Output
[1, 2, 3, 4, 5, 6, 7]
- Create an empty list
flat_list
. - Access each element of the sublist using a nested loop and append that element to
flat_list
.
3. Example 3: Using itertools package
import itertools my_list = [[1], [2, 3], [4, 5, 6, 7]] flat_list = list(itertools.chain(*my_list)) print(flat_list)
Output
[1, 2, 3, 4, 5, 6, 7]
Using itertools module, we can create a flattened list.
chain()
method from itertools module returns each element of each iterable (i.e. sub lists ).list()
converts those returned values into a list.
4. Example 4: Using sum()
my_list = [[1], [2, 3], [4, 5, 6, 7]] flat_list = sum(my_list, []) print(flat_list)
Output
[1, 2, 3, 4, 5, 6, 7]
- Provide two arguments to the
sum()
method:my_list
and an empty list (i.e.[ ]
). - sum() combines
my_list
and[ ]
to produce a flattened list.
5. Example 5: Using lambda and reduce()
from functools import reduce my_list = [[1], [2, 3], [4, 5, 6, 7]] print(reduce(lambda x, y: x+y, my_list))
Output
[1, 2, 3, 4, 5, 6, 7]
In the above example, reduce()
applies the lambda function to all the elements of my_list
.
Learn more about lambda expressions at Python Anonymous/Lambda Function.
Related posts:
Python List Comprehension
Python any()
Python divmod()
Python setattr()
Python List extend()
Python Set symmetric_difference_update()
Python Program to Capitalize the First Character of a String
Python isinstance()
Python Program to Sort a Dictionary by Value
Python Namespace and Scope
Python del Statement
Python sorted()
Python List
Python Program to Get the File Name From the File Path
Python if...else Statement
Python Program to Remove Duplicate Element From a List
Python String rfind()
Python Program to Convert Decimal to Binary Using Recursion
Python map()
Python bin()
Python Object Oriented Programming
Python Set difference()
Python Dictionary values()
Python String lstrip()
Python Program to Randomly Select an Element From the List
Python Program to Check Prime Number
Python vars()
Python String join()
Python String rstrip()
Building Chatbots with Python Using Natural Language Processing and Machine Learning - Sumit Raj
Python Program to Check if a Number is Odd or Even
Python Program to Find the Factors of a Number