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Yoel Macia Delgado
Asked: 2020-02-08 02:58:38 +0800 CST 2020-02-08 02:58:38 +0800 CST

Sum the value of a list of dictionaries with the same key

  • 772

I have a list of dictionaries

lst = [ {'x': 1, 'y': 2}, {'x': 1, 'y': 3 }, {'x': 2, 'y': 2 } ]

Dictionaries always have the same keys and it is the values ​​that change at all times.

So I would like to sum the value of the keys "y" when the key "x" has the same value.

The output should give:lst # [{'x': 1, 'y': 5 }, {'x': 2, 'y': 2 }].

python

3 Answers

  1. Best Answer

    One option is to use itertools.groupbyto group the dictionaries based on the value of the key 'x'. Once this is done, it is simple to use list compression to obtain the final list, adding the values ​​of the key 'y'(and also other keys if they exist):

    import itertools
from operator import itemgetter



lst = [{'x': 1, 'y': 2}, {'x': 1, 'y': 3 }, {'x': 2, 'y': 2 }]

grupos = itertools.groupby(sorted(lst, key=itemgetter('x')), key=itemgetter('x'))

res = [{'x': v, 'y': sum(dicc['y'] for dicc in diccs)} for v, diccs in grupos]

print(res)

    The output is [{'x': 1, 'y': 5}, {'x': 2, 'y': 2}].

    • 1

  2. Another workaround:

    from collections import defaultdict

lst = [{'x': 1, 'y': 2}, {'x': 1, 'y': 3 }, {'x': 2, 'y': 2 }]

aux = defaultdict(int)
for d in lst:
    aux[d['x']] += d['y']

res = [{'x':k, 'y':v} for (k,v) in res.items()]
    • 1

  3. I have solved the problem, like so.

    lst = [ {'x': 1, 'y': 2}, {'x': 1, 'y': 3 }, {'x': 2, 'y': 2 } ]

result_list = []
name_dict = {}
for dict_item in lst:
    x = dict_item['x']
    y = dict_item['y']
    if x in name_dict:
        pos = name_dict[x]
        result_list[pos] = {'x':x, 'y': (result_list[pos]['y']+y)}
    else:
        result_list.append(dict_item)
        name_dict[x] = len(result_list) - 1

print result_list
    • 0