Python | Value summation of key in dictionary

Last Updated : 26 Aug, 2019

Many operations such as grouping and conversions are possible using Python dictionaries. But sometimes, we can also have a problem in which we need to perform the aggregation of values of key in dictionary list. This task is common in day-day programming. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using sum() + list comprehension

This is the one-liner approach to perform the task of getting the sum of particular key while iterating to the similar keys in list of dictionaries using list comprehension.

# Python3 code to demonstrate working of
# Value summation of key in dictionary
# Using sum() + list comprehension
  
# Initialize list
test_list = [{'gfg' : 1, 'is' : 2, 'best' : 3},
             {'gfg' : 7, 'is' : 3, 'best' : 5},
             {'gfg' : 9, 'is' : 8, 'best' : 6}] 
  
# printing original list
print("The original list is : " + str(test_list))
  
# Value summation of key in dictionary
# Using sum() + list comprehension
res = sum(sub['gfg'] for sub in test_list)
  
# printing result
print("The sum of particular key is : " + str(res))

Output :

The original list is : [{‘best’: 3, ‘gfg’: 1, ‘is’: 2}, {‘best’: 5, ‘gfg’: 7, ‘is’: 3}, {‘best’: 6, ‘gfg’: 9, ‘is’: 8}]
The sum of particular key is : 17

Method #2 : Using sum() + itemgetter() + map()
The combination of these functions can also be used to perform this task. In this, the main difference is that the comprehension task is done by map() and the key access task is done by the itemgetter().

# Python3 code to demonstrate working of
# Value summation of key in dictionary
# Using sum() + itemgetter() + map()
import operator
  
# Initialize list
test_list = [{'gfg' : 1, 'is' : 2, 'best' : 3},
             {'gfg' : 7, 'is' : 3, 'best' : 5},
             {'gfg' : 9, 'is' : 8, 'best' : 6}] 
  
# printing original list
print("The original list is : " + str(test_list))
  
# Value summation of key in dictionary
# Using sum() + itemgetter() + map()
res = sum(map(operator.itemgetter('gfg'), test_list))
  
# printing result
print("The sum of particular key is : " + str(res))

Output :

The original list is : [{‘best’: 3, ‘gfg’: 1, ‘is’: 2}, {‘best’: 5, ‘gfg’: 7, ‘is’: 3}, {‘best’: 6, ‘gfg’: 9, ‘is’: 8}]
The sum of particular key is : 17

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Python | Value summation of key in dictionary