How can I combine dictionaries with the same keys?

user_1026811 0
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I have a list of dictionaries like so:

dicts = [
    {'key_a': valuex1,
     'key_b': valuex2,
     'key_c': valuex3},

    {'key_a': valuey1,
     'key_b': valuey2,
     'key_c': valuey3},

    {'key_a': valuez1,
     'key_b': valuez2,
     'key_c': valuez3}
]

I would like to take these and construct a big dictionary like so:

big_dict = {
    'key_a': [valuex1, valuey1, valuez1],
    'key_b': [valuex2, valuey2, valuez2],
    'key_c': [valuex3, valuey3, valuez3]
}

Is there any elegant "zip"-like way for me to do this?

All the keys are always going to be identical.

dictionary python
5 Answers

You can use collections.defaultdict. The benefit of this solution is it does not require keys to be consistent across dictionaries, and it still maintains the minimum O(n) time complexity.

from collections import defaultdict

dict_list = [{'key_a': 'valuex1', 'key_b': 'valuex2', 'key_c': 'valuex3'},
             {'key_a': 'valuey1', 'key_b': 'valuey2', 'key_c': 'valuey3'},
             {'key_a': 'valuez1', 'key_b': 'valuez2', 'key_c': 'valuez3'}]            

d = defaultdict(list)
for myd in dict_list:
    for k, v in myd.items():
        d[k].append(v)

Result:

print(d)

defaultdict(list,
            {'key_a': ['valuex1', 'valuey1', 'valuez1'],
             'key_b': ['valuex2', 'valuey2', 'valuez2'],
             'key_c': ['valuex3', 'valuey3', 'valuez3']})
user_92095460

If you are happy to use a 3rd party library you can use Pandas. The pd.DataFrame constructor accepts a list of dictionaries directly:

import pandas as pd

res = pd.DataFrame(dictList).to_dict(orient='list')

{'key_a': ['valuex1', 'valuey1', 'valuez1'],
 'key_b': ['valuex2', 'valuey2', 'valuez2'],
 'key_c': ['valuex3', 'valuey3', 'valuez3']}
user_92095460
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