These little guys are like a bag of chips inside another bag of chips. They can get pretty deep if you let them. But don’t worry, we’ve got your back with this guide to help you navigate the depths of list-ception.
First things first, what is a nested list? It’s simply a list that contains other lists as its elements. Here’s an example:
# Define a nested list with two sub-lists, each containing two elements
my_list = [['apple', 'banana'], ['orange', 'pear']]
# Print the nested list
print(my_list)
# Output: [['apple', 'banana'], ['orange', 'pear']]
# A nested list is a list that contains other lists as its elements
# The first sub-list contains the elements 'apple' and 'banana'
# The second sub-list contains the elements 'orange' and 'pear'
Now, let’s say you want to access the second element of the first nested list. You can do that by using indexing like this:
# Accessing the second element of the first nested list
# using indexing
# Define a nested list
my_list = [["apple", "banana", "orange"], ["grape", "kiwi", "pineapple"]]
# Use indexing to access the second element of the first nested list
print(my_list[0][1])
# Output: banana
# Explanation:
# The first index [0] refers to the first nested list in my_list.
# The second index [1] refers to the second element within that nested list.
# Therefore, the print statement will output the second element, which is "banana".
Nested lists could be used for all sorts of things, like representing a 2D game board or organizing data in a spreadsheet. But let’s not get too fancy just yet we’ve got some basics to cover first!
To add an element to a nested list, you can use the append() method on one of its inner lists:
# Create a nested list with two inner lists
my_list = [['apple', 'banana'], ['orange', 'pear']]
# Use the append() method to add 'grape' to the first inner list
my_list[0].append('grape')
# Print the updated nested list
print(my_list)
# Output: [['apple', 'banana', 'grape'], ['orange', 'pear']]
# The nested list now contains three elements in the first inner list and two elements in the second inner list
# This demonstrates how to add an element to a nested list using the append() method on one of its inner lists
But what if you want to add an entire list as a new element? You can do that too! Just use the append() method on the outer list and pass in your nested list:
# Create a list of lists with fruits
my_list = [['apple', 'banana'], ['orange', 'pear']]
# Create a new list with two fruits
new_list = ['kiwi', 'mango']
# Use the append() method to add the new list as a new element to the outer list
my_list.append(new_list)
# Print the updated list
print(my_list)
# Output: [['apple', 'banana'], ['orange', 'pear'], ['kiwi', 'mango']]
# The append() method adds the specified element to the end of the list
# In this case, the new list is added as a new element to the outer list
# The outer list now has three elements, each representing a list of fruits
Now, some best practices for modifying lists. When dealing with large lists, you want to avoid nested loops like the plague! They can make your code slow and inefficient. Instead, try using list comprehension it’s like coding sorcery that lets you create new lists with a single line of code.
Here’s an example:
# This script demonstrates the use of list comprehension to create a new list with values multiplied by 2 from an existing list.
# Define a list with integer values
my_list = [1, 2, 3, 4]
# Use list comprehension to create a new list with values multiplied by 2 from the original list
new_list = [x * 2 for x in my_list]
# Print the new list
print(new_list)
# Output: [2, 4, 6, 8]
Finally, time complexity. When adding to a list, you want to consider the time complexity of different methods. For example, appending an element at the end of a list has a time complexity of O(1), while inserting an element in the middle of a list can have a time complexity of O(n).