Group by multiple keys and summarize/average values of a list of dictionaries

Question

What is the most pythonic way to group by multiple keys and summarize/average values of a list of dictionaries in Python please? Say I have a list of dictionaries as below:<

Answer 1

I had some extra requirements on top of the original question. I wanted to pass the grouper around and not have to pass around the original order of the fields if you need to reconstruct the grouping key as a dict.

namedtuple() works quite well in that it allows you to sort and use ._asdict()

from collections import namedtuple

def get_grouper(fields):

    key = namedtuple('GroupingKey', fields)

    def get_key(row):
        return key(**{field: row[field] for field in fields})

    return get_key

rows = [
    {'a': 1, 'b': 1, 'c': 1},
    {'a': 1, 'b': 2, 'c': 3},
    {'a': 1, 'b': 1, 'c': 2},
    {'a': 1, 'b': 0},
    {'a': 1, 'b': 2, 'c': 4}
]

grouper = get_grouper(['a','b'])

rows = sorted(rows, key=grouper)

for k, g in groupby(rows, key=grouper):
    print(k, list(g))