Summing the contents of two collections.Counter() objects [duplicate]

Question

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• Is there any pythonic way to combine two dicts (adding values for keys that appear in both)? 18 answers

I am working with collections.Counter() counters. I would like to combine two of them in a meaningful manner.

Suppose I have 2 counters, say,

Counter({'menu': 20, 'good': 15, 'happy': 10, 'bar': 5})

and

Counter({'menu': 1, 'good': 1, 'bar': 3})

I am trying to end up with:

Counter({'menu': 21, 'good': 16, 'happy': 10,'bar': 8})

How can I do this?

Answer 1

All you need to do is add them:

>>> from collections import Counter
>>> a = Counter({'menu': 20, 'good': 15, 'happy': 10, 'bar': 5})
>>> b = Counter({'menu': 1, 'good': 1, 'bar': 3})
>>> a + b
Counter({'menu': 21, 'good': 16, 'happy': 10, 'bar': 8})

From the docs:

Several mathematical operations are provided for combining Counter objects to produce multisets (counters that have counts greater than zero). Addition and subtraction combine counters by adding or subtracting the counts of corresponding elements.