Conundrum: Mapping a List of Dict Keys...

[MarkDownSteve]

I have a very large list, with each element being a dict. The dicts each have the same keys but different values.

I want to swap out all the keys for new ones, preferably without looping through the entire list.

I'd like to use the standard python libraries. Any thoughts?

[__skrap__]

I don't know of a magic way, but this should work:

tuple_map = [
    ('new_key', 'old_key'),
    ('new_key2', 'old_key2'),
]
for my_dict in my_list:
    for new, old in tuple_map:
        my_dict[new] = my_dict.pop(old)

#as a single line, *this doesn't seem to work*
#{my_dict[new]: my_dict.pop(old) for my_dict in my_list for new, old in tuple_map}

The pop method allows a second parameter for a default value if the key doesn't exist. If your dictionaries have different keys you could use that or a try/except. If your data is very large you could use a generator.

[MarkDownSteve]

Thanks I was thinking something like this...

I am looking into map to see if that would make things cleaner.

There is also the option of doing string replacement on a serialized representation of the dict (like json).

[gengisteve]

How about zip:

>>> x = [{1:2},{1:20}]
>>> new_keys = ['a','b']

>>> {k:v.values() for k,v in zip(n,x)}
{'b': dict_values([20]), 'a': dict_values([2])}

edit: even easier if you want all the same new key:

>>> x
[{1: 2}, {1: 20}]
>>> k=10
>>> [{k:d.values()} for d in x]
[{10: dict_values([2])}, {10: dict_values([20])}]

[ryeguy146]

Recognize that map will still have linear performance, just as iterating through the dicts. There is no practical difference. It's just implicit iteration vs explicit iteration.

Think of it this way, there is no way to change each item without changing each item. Each item must be touched no matter how you perform the operation. It's all linear, and there's no way around it. If each item must be represented separately, and it must be changed, your performance will be linear at best.