switch key and values in a dict of lists

Question

Hello Stackoverflow people,

I have a nested dictionary with lists as values and I want to create a dict where all the list entries get their corresponding key as value.

Example time!

# what I have
dict1 = {"A":[1,2,3], "B":[4,5,6], "C":[7,8,9]}

# what I want
dict2 = {1:"A", 2:"A", 3:"A", 4:"B", 5:"B", 6:"B", 7:"C", 8:"C", 9:"C"}

Any help will be much appreciated!

Answer 1

Try this

dict1 = {"A":[1,2,3], "B":[4,5,6], "C":[7,8,9]}
dict2= {}
for keys,values in dict1.items():
    for i in values:
        dict2[i]=keys
print(dict2)

Output

{1: 'A', 2: 'A', 3: 'A', 4: 'B', 5: 'B', 6: 'B', 7: 'C', 8: 'C', 9: 'C'}

Hope it helps

Answer 2

Use dictionary comprehension:

d = {'a': 'b', 'c': 'd', 'e': 'f'}
d2 = dict((v1, k) for k, v in d.items() for v1 in v)  # Here is the one-liner

Answer 3

assuming your key: value dictionary contains list as a value and using dict comprehension.

Using a second loop to iterate over the list present in original dictionary.

{item: key for key, value in dict1.items() for item in value}