HereHere HereHere - 6 months ago 3
Python Question

How to sum dictionaries values with same key inside two list?

I have two list with dictionaries:

rich = [
{'currency': 'USD', 'value': 100},
{'currency': 'EUR', 'value': 110},
{'currency': 'USD', 'value': 120},
{'currency': 'GBP', 'value': 130},

poor = [
{'currency': 'USD', 'value': 10},
{'currency': 'AED', 'value': 20},

how can I combine both so that I can get:

rich_and_poor = [
{'currency': 'USD', 'value': 110}, # +10
{'currency': 'EUR', 'value': 110},
{'currency': 'GBP', 'value': 130},
{'currency': 'AED', 'value': 20} # new dictionary


from collections import Counter
is useful, because it can sum dictionaries values with same key, but I still can't figure out how to do it with list of dictionairies.

x = {'value': 123}
y = {'value': 2}

Counter(x) + Counter(y) = {'value': 125}


A more logical structure for this would be to have one dictionary, with currencies as keys and values as values. Let's use a defaultdict to create one (so that new keys start out as 0 automatically):

currencies = defaultdict(int)

Now add your dicts to it:

for currencydict in rich + poor:
    currencies[currencydict['currency']] += currencydict['value']

That yielded something like (not necessarily the same order):

    'USD': 230,
    'EUR': 110,
    'GBP': 130,
    'AED': 20

And now, if you really have to, convert it back to a list like yours:

rich_and_poor = [{'currency': key, 'value': value} for key, value in currencies.items()]