Python | Ways to invert mapping of dictionary

Last Updated : 18 Feb, 2019

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.

# 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}

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

# 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

# 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

# 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'}

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