CODEWITHSUNDEEP
python
HereHere
HereHere

Reputation: 762

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
]

?

The 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}

Upvotes: 0

Views: 1109

Answers (1)

RemcoGerlich
RemcoGerlich

Reputation: 31260

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()]

Upvotes: 1

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