Combining lists of dictionaries based on list index

Question

I feel like this question must have been asked previously but could not find it on Stack Overflow.

Is there a way to elegantly combine multiple lists of dictionaries

Answer 1

This will do what you want:

result = [{**x, **y} for x, y in zip(list_1, list_2)]

# [{'a': 'b', 'hello': 'world'}, {'c': 'd', 'foo': 'test'}]

See PEP 448 for an explanation of ** syntax.

For a generalised solution:

list_1=[{'hello':'world'},{'foo':'test'}]
list_2=[{'a':'b'},{'c':'d'}]
list_3=[{'e':'f'},{'g':'h'}]

lists = [list_1, list_2, list_3]

def merge_dicts(*dict_args):
    result = {}
    for dictionary in dict_args:
        result.update(dictionary)
    return result

result = [merge_dicts(*i) for i in zip(*lists)]

# [{'a': 'b', 'e': 'f', 'hello': 'world'}, {'c': 'd', 'foo': 'test', 'g': 'h'}]

Answer 2

For a generalizable solution, in Python 3, you could do something like:

In [14]: from operator import or_

In [15]: from functools import reduce

In [16]: list_of_lists = [list_1, list_2]

In [17]: [dict(reduce(or_, map(dict.items, ds))) for ds in zip(*list_of_lists)]
Out[17]: [{'a': 'b', 'hello': 'world'}, {'c': 'd', 'foo': 'test'}]

In Python 2, no need to import reduce, since it is already in the global namespace, but you will need to use dict.viewitems instead of dict.items:

[dict(reduce(or_, map(dict.viewitems, ds))) for ds in zip(*list_of_lists)]

Note the only real problem with your solution that I can see is that it uses for i in range(...), when you should just loop over the zippped lists.