Organized lists inside dictionary based off existing dictionary-CodePudding

I have an existing dictionary in Python that is formatted as follows, the length and values can change when the code is ran though.

{'1': 'Dog',
 '2': 'Dog',
 '3': 'Cat',
 '4': 'Dog',
 '5': 'Cat',
 '6': 'Cat',
 '7': 'Dog',
 '8': 'Dog',
 '9': 'Rabbit',
 '10': 'Dog',
 '11': 'Cat'}

I want to reformat it so it is as follows

{
 "Dog" : ['1', '2', '4', '7', '8', 10],
 "Cat" : ['3', '5', '6', '11'],
 "Rabbit" : ['9']
}

I am struggling to come up with a for loop that can loop through the existing dict and create the new one.

CodePudding user response：

You can use collections.defaultdict or dict.setdefault and insert element in list.

from collections import defaultdict

dct = defaultdict(list)
dct_2 = {}

inp = {'1': 'Dog','2': 'Dog','3': 'Cat','4': 'Dog',
 '5': 'Cat','6': 'Cat','7': 'Dog','8': 'Dog',
 '9': 'Rabbit','10': 'Dog','11': 'Cat'}


for k,v in inp.items():
    dct[v].append(k)
    
    dct_2.setdefault(v, []).append(k)
    
print(dct)
print(dct_2)

Output:

# dct
defaultdict(<class 'list'>, {'Dog': ['1', '2', '4', '7', '8', '10'], 'Cat': ['3', '5', '6', '11'], 'Rabbit': ['9']})

# dct_2
{'Dog': ['1', '2', '4', '7', '8', '10'], 'Cat': ['3', '5', '6', '11'], 'Rabbit': ['9']}