Merging Dictionaries in Python: Adding Values for Overlapping Keys
When working with multiple dictionaries, it's often necessary to combine them in a meaningful way. One common scenario involves adding the values of keys that appear in both dictionaries while keeping keys that only exist in one.
Problem:
Consider the following dictionaries:
Dict A: {'a': 1, 'b': 2, 'c': 3} Dict B: {'b': 3, 'c': 4, 'd': 5}
The goal is to merge these dictionaries such that the result is:
{'a': 1, 'b': 5, 'c': 7, 'd': 5}
Solution Using Collections.Counter:
A Pythonic and efficient way to achieve this is by using the collections.Counter class. It's a subclass of dict that provides a convenient way to do element-based counting, which lends itself well to the task of merging dictionaries.
from collections import Counter A = Counter({'a':1, 'b':2, 'c':3}) B = Counter({'b':3, 'c':4, 'd':5})
To merge the dictionaries, we simply add the Counter objects:
merged_dict = A + B
The result is a new Counter object, which automatically adds values for overlapping keys:
merged_dict.most_common() # Output: [('c', 7), ('b', 5), ('d', 5), ('a', 1)]
Converting it to a regular dictionary is trivial:
merged_dict = dict(merged_dict)
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