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]}

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