Python: Increment value of dictionary stored in a list

Question

Simple example here:

I want to have a list which is filled with dictionaries for every type of animal.

The print should look like this:

dictlist_animals = [{'type':'horse','amount':2},
                    {'type':'monkey','amount':2},
                    {'type':'cat','amount':1},
                    {'type':'dog','amount':1}]

Because some animals exist more than once I've added a key named 'amount' which should count how many animals of every type exist.

I am not sure if the 'if-case' is correctly and what do I write in the 'else case'?

dictlist_animals = []

animals = ['horse', 'monkey', 'cat', 'horse', 'dog', 'monkey']


for a in animals:
    if a not in dictlist_animals['type']:
        dictlist_animals.append({'type': a, 'amount' : 1})

    else:
        #increment 'amount' of animal a

Answer 1

Better to use Counter . It's create dictionary where keys are elements of animals list and values are their count. Then you can use list comprehension for creating list with dictionaries:

from collections import Counter

animals_dict = [{'type': key, 'amount': value} for key, value in Counter(animals).items()]

Answer 2

Try below code,

dictlist_animals = []

animals = ['horse', 'monkey', 'cat', 'horse', 'dog', 'monkey']
covered_animals = []
for a in animals:
    if a in covered_animals:
        for dict_animal in dictlist_animals:
            if a == dict_animal['type']:
                dict_animal['amount'] = dict_animal['amount'] + 1
    else:
        covered_animals.append(a)
        dictlist_animals.append({'type': a, 'amount' : 1})
print dictlist_animals

[{'amount': 2, 'type': 'horse'}, {'amount': 2, 'type': 'monkey'}, {'amount': 1, 'type': 'cat'}, {'amount': 1, 'type': 'dog'}]

Answer 3

You can't directly call dictlist_animals['type'] on a list because they are indexed numerically. What you can do is to store this data in an intermediate dictionary and then convert it in the data structure you want:

dictlist_animals = []

animals = ['horse', 'monkey', 'cat', 'horse', 'dog', 'monkey']

animals_count = {};
for a in animals:
    c = animals_count.get(a, 0)
    animals_count[a] = c+1

for animal, amount in animals_count.iteritems():
    dictlist_animals.append({'type': animal, 'amount': amount})

Note that c = animals_count.get(a, 0) gets the current amount for the animal a if it is present, otherwise it returns the default value 0 so that you don't have to use an if/else statement.

Answer 4

You can also use defaultdict .

from collections import defaultdict
d = defaultdict(int)
for animal in animals:
    d[animal]+= 1

dictlist_animals = [{'type': key, 'amount': value}  for key, value in d.iteritems()]