Write a python program to combine two dictionaries adding values for common keys

Given two dictionaries, the task is to combine the dictionaries such that we get the added values for common keys in the resultant dictionary. 
Example: 

Input: dict1 = {'a': 12, 'for': 25, 'c': 9}
       dict2 = {'Geeks': 100, 'geek': 200, 'for': 300}

Output: {'for': 325, 'Geeks': 100, 'geek': 200}

Let’s see some of the methods on How to  Combine two dictionaries by adding values for common keys in Python. 

Naive Method to Combine two dictionary adding values for common keys

Here we are iterating over the dictionaries and adding the values for the same keys.

Python3

dict1 = {'a': 12, 'for': 25, 'c': 9}

dict2 = {'Geeks': 100, 'geek': 200, 'for': 300}

for key in dict2:

    if key in dict1:

        dict2[key] = dict2[key] + dict1[key]

    else:

        pass

print[dict2]

Output:

{'Geeks': 100, 'geek': 200, 'for': 325}

Using Union Method  to Combine two dictionary adding values for common keys

Here we are using the set union method and with the help of get[] function we are fetching the value for that particular keys.

Python3

dict1 = {'a': 12, 'for': 25, 'c': 9}

dict2 = {'Geeks': 100, 'geek': 200, 'for': 300}

c = {i: dict1.get[i, 0] + dict2.get[i, 0]

     for i in set[dict1].union[dict2]}

print[c]

Output:

{'for': 325, 'a': 12, 'geek': 200, 'Geeks': 100, 'c': 9}

Using collections.Counter[]  to Combine two dictionary adding values for common keys

Here we are using the collections module to calculate the combination of two dictionaries by adding the values for common keys.

Python3

from collections import Counter

dict1 = {'a': 12, 'for': 25, 'c': 9}

dict2 = {'Geeks': 100, 'geek': 200, 'for': 300}

Cdict = Counter[dict1] + Counter[dict2]

print[Cdict]

Output:

Counter[{'for': 325, 'geek': 200, 'Geeks': 100, 'a': 12, 'c': 9}]

Using itertools.chain[]  to Combine two dictionary adding values for common keys

Here we are using the itertools module to Combine two dictionary by adding values for common keys uisng the chain[].

Python3

import itertools

import collections

dict1 = {'a': 12, 'for': 25, 'c': 9}

dict2 = {'Geeks': 100, 'geek': 200, 'for': 300}

Cdict = collections.defaultdict[int]

for key, val in itertools.chain[dict1.items[], dict2.items[]]:

    Cdict[key] += val

print[dict[Cdict]]

Output:

{'a': 12, 'for': 325, 'c': 9, 'Geeks': 100, 'geek': 200}

Using functools.reduce and dict comprehension to Combine two dictionary adding values for common keys

Here we are using the functools.reduce[] function with the help of dictionary comprehension we are combining two dictionaries.

Python3

from functools import reduce

dict_seq = [

  {'a': 1, 'b': 2, 'c': 3},

  {'a':10, 'b': 20},

  {'b': 100},

]

print[reduce[lambda d1,d2: {k: d1.get[k,0]+d2.get[k,0]

for k in set[d1]|set[d2]}, dict_seq]]

Output:

{'a': 11, 'b': 122, 'c': 3}

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