Python sum on keys for List of Dictionaries [duplicate]

Answer 1

Example solution

I am not sure it is "beautiful/Pythonic enough", but it is surely short and works without additional modules:

def get_amt(name):
    return lambda x: x['amt'] if x['Name']==name else 0

names = sorted(set(map(lambda x: x['Name'], data)))
result = [{'Name':name,'amt':sum(map(get_amt(name), data))} for name in names]

Proof

Proof is here: http://codepad.org/L1gcTpVK

If you supply data as in the question, the result will be equal to this:

[{'Name': 'A', 'amt': 1000}, {'Name': 'B', 'amt': 200}, {'Name': 'C', 'amt': 900}]

which is exactly as requested :)

Answer 2

You can do it like this:

def sum(dict_list):
    result_list = []
    name_dict = {}
    for dict_item in dict_list:
        name = dict_item['Name']
        amt = dict_item['amt']
        if name_dict.has_key(name):
            pos = name_dict[name]
            result_list[pos] = {'Name':name, 'amt': (result_list[pos]['amt']+amt)}
        else:
            result_list.append(dict_item)
            name_dict[name] = len(result_list) - 1
    return result_list

Answer 3

from collections import defaultdict

c = defaultdict(int)
for d in list_of_dictionaries:
    c[d['Name']] += d['amt']

It produces c:

{'A': 1000, 'C': 900, 'B': 200}

To convert it to list of dictionaries:

[{'Name': name, 'amt': amt} for name, amt in c.items()]

Result:

[{'Name': 'A', 'amt': 1000}, {'Name': 'C', 'amt': 900}, {'Name': 'B', 'amt':200}]

Answer 4

Another possible solution, this time using itertools:

lst = [
{'Name': 'A', 'amt':100},
{'Name': 'B', 'amt':200},
{'Name': 'A', 'amt':300},
{'Name': 'C', 'amt':400},
{'Name': 'C', 'amt':500},
{'Name': 'A', 'amt':600}]

import itertools as it
keyfunc = lambda x: x['Name']

groups = it.groupby(sorted(lst, key=keyfunc), keyfunc)
[{'Name':k, 'amt':sum(x['amt'] for x in g)} for k, g in groups]

Answer 5

output_dict = {}
for i in dict_list:
    if i['Name'] in output_dict:
        output_dict[i['Name']] = i['amt']
    else:
        output_dict[i['Name']] += i['amt']

Will give you a dictionary where the keys are names and amounts are values. If you must have it as a list of dicts:

[{'Name':key, 'amt':value} for key, value in output_dict.items()]