30-seconds-of-code/snippets/combine_values.md

title, tags, expertise, author, firstSeen, lastUpdated

title	tags	expertise	author	firstSeen	lastUpdated
Combine dictionary values	dictionary	intermediate	maciv	2021-03-07T12:30:47+02:00	2021-04-04T14:32:35+03:00

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]}