How to add similar key value in python?

Question

This is the array of data:

Input Data:

list1 = [{'user': 1, 'coins': 2}, {'user': 18, 'coins': 8}, {'user': 1, 'coins': 1}, {'user': 3, 'coins': 1}, {'user': 5, 'coins': 1}, {'user': 7, 'coins': 0}, {'user': 18, 'coins': 0}]

Expected Outcome:

list2 = [{'user': 1, 'coins': 3}, {'user': 18, 'coins': 8}, {'user': 3, 'coins': 1}, {'user': 5, 'coins': 1}, {'user': 7, 'coins': 0}]

So, there will be list1, and we have to add the coins to similar user which can be identified by user key value. If user key have similar value that is 1 (in above case) then coins of both or multiple user must be added making it a total sum of that user coins.

In above example, we can see that user with 1 as value in 2 different dict got added and total sum was given in list 2.

Answer 1

This can be easily done using a collections.defaultdict as intermediate data object:

import collections
dd = collections.defaultdict(int)
for d in list1:
    dd[d['user']] += d['coins']
list2 = [{'user': user, 'coins': coins} for user, coins in dd.items()]

or similary, using a collections.Counter object:

cntr = collections.Counter()
for d in list1:
    cntr[d['user']] += d['coins']
list2 = [{'user': user, 'coins': coins} for user, coins in cntr.items()]