Combine dictionary values

Python, Dictionary · Apr 4, 2021

Combines two or more dictionaries, creating a list of values for each key.

Create a new collections.defaultdict with list as the default value for each key and loop over dicts.
Use dict.append() to map the values of the dictionary to keys.
Use dict() to convert the collections.defaultdict to a regular dictionary.

from collections import defaultdict

def combine_values(*dicts):
  res = defaultdict(list)
  for d in dicts:
    for key in d:
      res[key].append(d[key])
  return dict(res)

d1 = {'a': 1, 'b': 'foo', 'c': 400}
d2 = {'a': 3, 'b': 200, 'd': 400}

combine_values(d1, d2) # {'a': [1, 3], 'b': ['foo', 200], 'c': [400], 'd': [400]}