如何将字典与相同的键结合起来？

Question

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.

Answer 1

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]}

Answer 2

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']})

Answer 3

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)

Answer 4

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']}

Answer 5

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]))
    }