Python | Sum list of dictionaries with same key

Difficulty Level : Easy
Last Updated : 03 Mar, 2019

You have given a list of dictionaries, the task is to return a single dictionary with sum values with the same key.

Let’s discuss different methods to do the task.

Method #1: Using reduce() + operator

# Python code to demonstrate
# return the sum of values of dictionary
# with same keys in list of dictionary
  
import collections, functools, operator
  
# Initialising list of dictionary
ini_dict = [{'a':5, 'b':10, 'c':90},
            {'a':45, 'b':78}, 
            {'a':90, 'c':10}]
  
  
# printing initial dictionary
print ("initial dictionary", str(ini_dict))
  
# sum the values with same keys
result = dict(functools.reduce(operator.add,
         map(collections.Counter, ini_dict)))
  
print("resultant dictionary : ", str(result))

Output:

initial dictionary [{‘b’: 10, ‘a’: 5, ‘c’: 90}, {‘b’: 78, ‘a’: 45}, {‘a’: 90, ‘c’: 10}]
resultant dictionary : {‘b’: 88, ‘a’: 140, ‘c’: 100}

Method #2: Using counter

# Python code to demonstrate
# return the sum of values of dictionary
# with same keys in list of dictionary
  
import collections
  
# Initialising list of dictionary
ini_dict = [{'a':5, 'b':10, 'c':90}, 
            {'a':45, 'b':78},
            {'a':90, 'c':10}]
  
# printing initial dictionary
print ("initial dictionary", str(ini_dict))
  
# sum the values with same keys
counter = collections.Counter()
for d in ini_dict: 
    counter.update(d)
      
result = dict(counter)
  
  
print("resultant dictionary : ", str(counter))

Output:

initial dictionary [{‘c’: 90, ‘a’: 5, ‘b’: 10}, {‘a’: 45, ‘b’: 78}, {‘a’: 90, ‘c’: 10}]
resultant dictionary : Counter({‘a’: 140, ‘c’: 100, ‘b’: 88})

Method #3: Naive Method

# Python code to demonstrate
# return the sum of values of dictionary
# with same keys in list of dictionary
  
from operator import itemgetter
  
# Initialising list of dictionary
ini_dict = [{'a':5, 'b':10, 'c':90},
            {'a':45, 'b':78}, 
            {'a':90, 'c':10}]
  
# printing initial dictionary
print ("initial dictionary", str(ini_dict))
  
# sum the values with same keys
result = {}
for d in ini_dict:
    for k in d.keys():
        result[k] = result.get(k, 0) + d[k]
  
  
print("resultant dictionary : ", str(result))

Output:

initial dictionary [{‘b’: 10, ‘c’: 90, ‘a’: 5}, {‘b’: 78, ‘a’: 45}, {‘c’: 10, ‘a’: 90}]
resultant dictionary : {‘b’: 88, ‘c’: 100, ‘a’: 140}

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