CODEWITHSUNDEEP
pythondictionary
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Reputation: 424

How can I combine dictionaries with the same keys?

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.

Upvotes: 15

Views: 25477

Answers (5)

jpp
jpp

Reputation: 164623

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']})

Upvotes: 7

Ned Batchelder
Ned Batchelder

Reputation: 375494

big_dict = {}
for k in dicts[0]:
    big_dict[k] = [d[k] for d in dicts]

Or, with a dict comprehension:

{k: [d[k] for d in dicts] for k in dicts[0]}

Upvotes: 17

jpp
jpp

Reputation: 164623

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']}

Upvotes: 0

jazzblue
jazzblue

Reputation: 2437

You can merge dictionaries in the following way:

def merge_dicts(dict_list, separator=''):
    """
    Merges list of dictionaries to a single dictionary, Concatenates values with the same key.
    :param dict_list: list of dictionaries to be merged.
    :param separator: separator to be inserted between values of same key.
    :return: Merged dictionary.
    """
    return {k1: separator.join([d[k1] for d in dict_list if k1 in d])
            for k1 in set(reduce(lambda x, y: x+y, [k.keys() for k in dict_list]))
    }

Upvotes: -1

BrenBarn
BrenBarn

Reputation: 251355

If all the dicts have the same set of keys, this will work:

dict((k, [d[k] for d in dictList]) for k in dictList[0])

If they may have different keys, you'll need to first built a set of keys by doing set unions on the keys of the various dicts:

allKeys = reduce(operator.or_, (set(d.keys()) for d in dictList), set())

Then you'll need to protect against missing keys in some dicts:

dict((k, [d[k] for d in [a, b] if k in d]) for k in allKeys)

Upvotes: 2

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