How to Flatten a List of Lists in Python

1. Introduction

In Python, a list of lists is a common way to represent a matrix or a 2D array. However, sometimes we need to convert this structure into a single, flat list where all the elements are in a single dimension. Flattening a list of lists can be useful in data processing, where you want to aggregate all elements for analysis or operations without the complexity of nested structures.


Flattening a list of lists means converting a multi-dimensional list into a one-dimensional list. This operation takes all the elements from the nested lists and places them in a single list without any nested structures.

2. Program Steps

1. Create a list of lists that you want to flatten.

2. Use list comprehension to iterate through each element in each nested list.

3. Append each element to a new list to achieve a flat structure.

4. Output the resulting flat list.

3. Code Program

# Step 1: Create a list of lists
list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Step 2: Flatten the list of lists using list comprehension
flat_list = [item for sublist in list_of_lists for item in sublist]

# The output can be printed or used elsewhere in your program


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


1. list_of_lists is our initial multi-dimensional list.

2. flat_list is created using list comprehension, which iterates through each sublist in the list_of_lists and then iterates through each item within those sublists.

3. Each item from the sublists is appended to flat_list.

4. The print function is used to display the flattened list.

5. The output shows all elements from the nested lists in a single, flattened list.