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Python | Subtraction of dictionaries

  • Last Updated : 26 Jul, 2019

Sometimes, while working with dictionaries, we might have utility problem in which we need to perform elementary operation among the common keys of dictionaries. This can be extended to any operation to be performed. Let’s discuss subtraction of like key values and ways to solve it in this article.

Method #1 : Using dictionary comprehension + keys()
The combination of above two can be used to perform this particular task. This is just a shorthand to the longer method of loops and can be used to perform this task in one line.




# Python3 code to demonstrate working of
# Subtraction of dictionaries
# Using dictionary comprehension + keys()
  
# Initialize dictionaries
test_dict1 = {'gfg' : 6, 'is' : 4, 'best' : 7}
test_dict2 = {'gfg' : 10, 'is' : 6, 'best' : 10}
  
# printing original dictionaries 
print("The original dictionary 1 : " +  str(test_dict1))
print("The original dictionary 2 : " +  str(test_dict2))
  
# Using dictionary comprehension + keys()
# Subtraction of dictionaries
res = {key: test_dict2[key] - test_dict1.get(key, 0)
                       for key in test_dict2.keys()}
  
# printing result 
print("The difference dictionary is : " + str(res))
Output :
The original dictionary 1 : {'gfg': 6, 'is': 4, 'best': 7}
The original dictionary 2 : {'gfg': 10, 'is': 6, 'best': 10}
The difference dictionary is : {'gfg': 4, 'is': 2, 'best': 3}

 

Method #2 : Using Counter() + "-" operator
The combination of above method can be used to perform this particular task. In this, the Counter function converts the dictionary in the form in which the minus operator can perform the task of subtraction.






# Python3 code to demonstrate working of
# Subtraction of dictionaries
# Using Counter() + "-" operator
from collections import Counter
  
# Initialize dictionaries
test_dict1 = {'gfg' : 6, 'is' : 4, 'best' : 7}
test_dict2 = {'gfg' : 10, 'is' : 6, 'best' : 10}
  
# printing original dictionaries 
print("The original dictionary 1 : " +  str(test_dict1))
print("The original dictionary 2 : " +  str(test_dict2))
  
# Using Counter() + "-" operator
# Subtraction of dictionaries
temp1 = Counter(test_dict1)
temp2 = Counter(test_dict2)
res = temp2 - temp1
  
# printing result 
print("The difference dictionary is : " + str(dict(res)))
Output :
The original dictionary 1 : {'gfg': 6, 'is': 4, 'best': 7}
The original dictionary 2 : {'gfg': 10, 'is': 6, 'best': 10}
The difference dictionary is : {'gfg': 4, 'is': 2, 'best': 3}

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