Python | Ways to invert mapping of dictionary (original) (raw)

Last Updated : 11 Jul, 2025

Dictionary is a collection which is unordered, changeable and indexed. In Python, dictionaries are written with curly brackets, and they have keys and values. It is widely used in day to day programming, web development, and machine learning. Let's discuss a few ways to invert mapping of a dictionary.

Method #1: Using Dictionary Comprehension.

Python3 `

Python code to demonstrate

how to invert mapping

using dict comprehension

initialising dictionary

ini_dict = {101: "akshat", 201 : "ball"}

print initial dictionary

print("initial dictionary : ", str(ini_dict))

inverse mapping using dict comprehension

inv_dict = {v: k for k, v in ini_dict.items()}

print final dictionary

print("inverse mapped dictionary : ", str(inv_dict))

`

Output:

initial dictionary : {201: 'ball', 101: 'akshat'} inverse mapped dictionary : {'ball': 201, 'akshat': 101}

Time complexity: O(n), where n is the number of key-value pairs in the dictionary.
Auxiliary space: O(n), to store the keys and values in dictionary.

Method #2: Using dict.keys() and dict.values()

Python3 `

Python code to demonstrate

how to invert mapping

using zip and dict functions

initialising dictionary

ini_dict = {101: "akshat", 201 : "ball"}

print initial dictionary

print("initial dictionary : ", str(ini_dict))

inverse mapping using zip and dict functions

inv_dict = dict(zip(ini_dict.values(), ini_dict.keys()))

print final dictionary

print("inverse mapped dictionary : ", str(inv_dict))

`

Output:

initial dictionary : {201: 'ball', 101: 'akshat'} inverse mapped dictionary : {'ball': 201, 'akshat': 101}

Method #3: Using map() and reversed

Python3 `

Python code to demonstrate

how to invert mapping

using map and reversed

initialising dictionary

ini_dict = {101: "akshat", 201 : "ball"}

print initial dictionary

print("initial dictionary : ", str(ini_dict))

inverse mapping using map and reversed

inv_dict = dict(map(reversed, ini_dict.items()))

print final dictionary

print("inverse mapped dictionary : ", str(inv_dict))

`

Output:

initial dictionary : {201: 'ball', 101: 'akshat'} inverse mapped dictionary : {'akshat': 101, 'ball': 201}

Method #4: Using lambda

Python3 `

Python code to demonstrate

how to invert mapping

using lambda

initialising dictionary

ini_dict = {101 : "akshat", 201 : "ball"}

print initial dictionary

print("initial dictionary : ", str(ini_dict))

inverse mapping using lambda

lambda ini_dict: {v:k for k, v in ini_dict.items()}

print final dictionary

print("inverse mapped dictionary : ", str(ini_dict))

`

Output:

initial dictionary : {201: 'ball', 101: 'akshat'} inverse mapped dictionary : {201: 'ball', 101: 'akshat'}

The time complexity of this code is O(n), where n is the number of key-value pairs in the dictionary ini_dict. dictionary.

The auxiliary space complexity of this code is O(n), where n is the number of key-value pairs in the dictionary ini_dict.

Method #5: Using the zip function and dictionary constructor:

Approach:

• Use the zip function to create a list of tuples with the original dictionary's values and keys
• Pass the list of tuples to the dictionary constructor to create the inverted dictionary
• Return the inverted dictionary Python3 `

original_dict = {"a": 1, "b": 2, "c": 3} inverted_dict = dict(zip(original_dict.values(), original_dict.keys())) print(inverted_dict)

`

Output

{1: 'a', 2: 'b', 3: 'c'}

Time complexity: O(n), where n is the number of key-value pairs in the dictionary
Space complexity: O(n), where n is the number of key-value pairs in the dictionary