My list of list looks something like this:
[[4,'apples'],[3,'oranges'],[4,'bananas'],[2,'apples'],[2,'pineapple'],[3,'apples']]
I want to create a dictionary from this, where the values of each item is listed: for example, I want the following output:
{4:'apples','bananas', 3:'oranges','apples', 2:'apples', 'pineapple'}
dict.setdefault can help here if you don't want to use collections.defaultdict:
lst = [[4,'apples'],[3,'oranges'],[4,'bananas'],[2,'apples'],[2,'pineapple'],[3,'apples']]
dct = {}
for num, name in lst:
dct.setdefault(num, []).append(name)
print(dct)
#{2: ['apples', 'pineapple'],
# 3: ['oranges', 'apples'],
# 4: ['apples', 'bananas']}
However defaultdict is generally the better and more general solution.
dctsetdefault = dct.setdefault and use that inside the loop! But the actual timing depends on the length of the list and the number of duplicate keys (maybe even on other stuff as well). If speed is a concern use iteration_utilities.groupedby(lst, key=operator.itemgetter(0), keep=operator.itemgetter(1)) (but requires importing the operator-module and an external library).Code agency at your service:
lst = [['4','apples'],['3','oranges'],['4','bananas'],['2','apples'],['2','pineapple'],['3','apples']]
result = {}
for item in lst:
key = item[0]
try:
result[key].append(item[1])
except:
result[key] = [item[1]]
print(result)
# {'3': ['oranges', 'apples'], '2': ['apples', 'pineapple'], '4': ['apples', 'bananas']}
As stated by @Jean-Francois Fabre, this solutions is rather slow: 3,5 seconds bs 5.7 seconds for 100000 iterations with 3,5 being the solution with defaultdict.
Using collections.defaultdict:
result = defaultdict(list)
for key, value in [[4,apples],[3,oranges],[4,bananas],[2,apples],[2,pineapple],[3,apples]]:
result[key].append(value)
collections.defaultdict might be useful to you.
from collections import defaultdict
items = [
[4, "apples"],
[3, "oranges"],
[4, "bananas"],
[2, "apples"],
[2, "pineapple"],
[3, "apples"]
]
mapping = defaultdict(list)
for number, name in items:
mapping[number].append(name)
Examples of official document of defaultdict would be helpful to you.
https://docs.python.org/3/library/collections.html#defaultdict-examples
4:['apples','bananas']?