Question

This is a great primer but doesn’t answer what I need:
Combining two sorted lists in Python

I have two Python lists, each is a list of datetime,value pairs:

list_a = [['1241000884000', 3], ['1241004212000', 4], ['1241006473000', 11]]

And:

list_x = [['1241000884000', 16], ['1241000992000', 16], ['1241001121000', 17], ['1241001545000', 19], ['1241004212000', 20], ['1241006473000', 22]]

1. There are actually numerous list_a lists with different key/values.
2. All list_a datetimes are in list_x.
3. I want to make a list, list_c, corresponding to each list_a which has each datetime from list_x and value_a/value_x.

Bonus:

In my real program, list_a is actually a list within a dictionary like so. Taking the answer to the dictionary level would be:

dict = {object_a: [['1241000884000', 3], ['1241004212000', 4], ['1241006473000', 11]], object_b: [['1241004212000', 2]]}

I can figure that part out though.

Answer 1

Here’s some code that does what you asked for. You can turn your list of pairs into a dictionary straightforwardly. Then keys that are shared can be found by intersecting the sets of keys. Finally, constructing the result dictionary is easy given the set of shared keys.

dict_a = dict(list_a)
dict_x = dict(list_x)

shared_keys = set(dict_a).intersection(set(dict_x))

result = dict((k, (dict_a[k], dict_x[k])) for k in shared_keys)