How to sum elements in list of dictionaries if two key values are the same

Question

I have the following list of dictionaries:

dictionary =[{'Flow': 100, 'Location': 'USA', 'Name': 'A1'},
            {'Flow': 90, 'Location': 'Europe', 'Name': 'B1'},
            {'Flow': 20, 'Location': 'USA', 'Name': 'A1'},
            {'Flow': 70, 'Location': 'Europe', 'Name': 'B1'}]

I want to create a new list of dictionaries, with summed Flow values of all dictionaries where Location and Name are the same. My desired output would be:

new_dictionary =[{'Flow': 120, 'Location': 'USA', 'Name': 'A1'},
            {'Flow': 160, 'Location': 'Europe', 'Name': 'B1'},]

How can I achieve this?

Answer 1

This is possible, but non-trivial to implement in python. Might I suggest using pandas? This is simple with a groupby, sum, and to_dict.

import pandas as pd

(pd.DataFrame(dictionary)
   .groupby(['Location', 'Name'], as_index=False)
   .Flow.sum()
   .to_dict('r'))

[{'Flow': 160, 'Location': 'Europe', 'Name': 'B1'},
 {'Flow': 120, 'Location': 'USA', 'Name': 'A1'}]

To install, use pip install --user pandas.

---

Otherwise, you can apply a pseudo-generic group operation using itertools.groupby.

from itertools import groupby
from operator import itemgetter

grouper = ['Location', 'Name']
key = itemgetter(*grouper)
dictionary.sort(key=key)

[{**dict(zip(grouper, k)), 'Flow': sum(map(itemgetter('Flow'), g))} 
    for k, g in groupby(dictionary, key=key)]

[{'Flow': 160, 'Location': 'Europe', 'Name': 'B1'},
 {'Flow': 120, 'Location': 'USA', 'Name': 'A1'}]