list union with duplicates

Question

I need to unite two lists in Python3,where duplicates can exist,and for one set of these the resulting list will contain as many as max in both lists.An example might clarify it:

[1,2,2,5]( some operator)[2,5,5,5,9]=[1,2,2,5,5,5,9]

Ideas?

Answer 1

You can use the collections.Counter class:

>>> from collections import Counter
>>> combined = Counter([1,2,2,5]) | Counter([2,5,5,5,9])
>>> list(combined.elements())
[1, 2, 2, 5, 5, 5, 9]

It functions as a multiset (an unordered collection where each element can appear multiple times). The | operator gives you the union of the multisets, where each element appears max(apperances_in_counter1, appearances_in_counter2) times.

This class was added in Python 2.7 and 3.1.