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.
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