Merge values of same key, in list of dicts

Question

I am relatively new to python 2.7, and can't figure out the following despite searching extensively on StackOverflow:

I have a list of dicts I wan't to combine, when key is the same, and add specific values (in the example 'price').

Input:

[{'id1': 'a', 'price': '2', 'color': 'green'}, {'id1': 'b', 'price': '5', 'color': 'red'}, {'id1': 'a', 'price': '2', 'color': 'green'}] 

Expected:

[{'id1': 'a', 'price': '4', 'color': 'green'}, {'id1': 'b', 'price': '5', 'color': 'red'}]

Answer 1

Same idea as your question before the edit.

>>> data = [{'id1': 'a', 'price': '2', 'color': 'green'},
...         {'id1': 'b', 'price': '5', 'color': 'red'},
...         {'id1': 'a', 'price': '2', 'color': 'green'}]

Construct a temporary dictionary and accumulate values in it

>>> temp = {}
>>> for d in data:
...     if d['id1'] not in temp:
...         temp[d['id1']] = {}
...     temp_d = temp[d['id1']]
...     temp_d['price'] = temp_d.get('price', 0) + int(d['price'])
...     temp_d.setdefault('colors', set()).add(d['color'])
... 
>>> temp
{'a': {'colors': {'green'}, 'price': 4}, 'b': {'colors': {'red'}, 'price': 5}}

Then using list comprehension and dictionary comprehension, reconstruct the list of dictionaries.

>>> [{'id1': k, 'price': v['price'], 'colors': v['colors']} for k, v in temp.items()]
[{'id1': 'a', 'colors': {'green'}, 'price': 4}, {'id1': 'b', 'colors': {'red'}, 'price': 5}]

---

>>> data = [{'id1': 'a', 'price': '2'}, {'id1': 'b', 'price': '5'},
...         {'id1': 'a', 'price': '2'}]

Create a temporary dictionary where we can accummulate the sum of prices against their ids,

>>> temp = {}
>>> for d in data:
...     temp[d['id1']] = temp.get(d['id1'], 0) + int(d['price'])
... 
>>> temp
{'a': 4, 'b': 5}

Here we try to get the value of d['id1'] from temp and if it is not found, 0 will be returned. We then add the price from the current dictionary and store the result back in the temp against the current id1.

Then reconstruct the list of dictionaries, with list comprehension and dictionary comprehension, like this

>>> [{'id1': k, 'price': temp[k]} for k in temp]
[{'price': 4, 'id1': 'a'}, {'price': 5, 'id1': 'b'}]

Answer 2

I've managed to compact the code like this:

import itertools as it
from operator import itemgetter

grupos = it.groupby(sorted(data, key=itemgetter('id1')), key=itemgetter('id1'))
res = [{'id1': v, 'price': sum(int(dicc['price']) for dicc in diccs) } for v, diccs in 
grupos]
print(res)

the output is:

[{'id1': 'a', 'price': 4}, {'id1': 'b', 'price': 25}, {'id1': 'c', 'price': 2}, {'id1': 'd', 'price': 1}, {'id1': 'e', 'price': 20}]