I am new to python and am learning how to do things the right way.

I have list of dictionaries `d`. Each dictionary represents users, and contains information like user\_id, age, etc. This list `d` can contain several dictionaries that represent the same user (but with slightly different information that does not matter for my purposes). I want to create histogram that shows how many users are in `d` with given age. How to do it in efficient way?

Edit:
I want to emphasise that I need to eliminate duplicates in the list.