CODEWITHSUNDEEP
pythonpython-3.xdictionary
Kinor
Kinor

Reputation: 55

Invert a dictionary inplace

I have a dictionary with unique values and I want to invert it (i.e. swap keys with values) inplace. Is there any way doing it without using another dictionary?

I would prefer to just manipulate the items inside the dict than use a new dictionary, so that id(my_dict) would remain the same.

Upvotes: 1

Views: 951

Answers (2)

Noctis Skytower
Noctis Skytower

Reputation: 22001

If you are trying to swap keys and values and do not mind duplicate values creating key conflicts, you can "reverse" the dictionary rather easily with a single line of code:

dictionary = dict(map(reversed, dictionary.items()))

If you would rather use the dictionary comprehension syntax instead, you can write this line:

dictionary = {value: key for key, value in dictionary.items()}

If you do not want to use the items method of the dictionary, it is rather easy to avoid:

dictionary = {dictionary[key]: key for key in dictionary}

If you can afford creating a copy of the dictionary, you can reverse it in place if needed:

def reverse_in_place(dictionary):
    reference = dictionary.copy()
    dictionary.clear()
    dictionary.update(map(reversed, reference.items()))

Upvotes: 2

Robbe
Robbe

Reputation: 2793

I guess you want to swap the keys and the values of the dict?

You can do it like this:

dict_name = dict(zip(dict_name.values(), dict_name.keys()))

Upvotes: 0

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