How to Filter a Dictionary to Retain Specific Keys?

Filtering a Dictionary to Retain Specific Keys

Often when working with dictionaries, it is necessary to refine them to contain only a certain subset of keys. This article explores two methods to achieve this: constructing a new dictionary with the desired keys or removing unwanted keys in-place.

Constructing a New Dictionary

The first method involves creating a new dictionary containing only the keys of interest. This can be accomplished using dictionary comprehension, as demonstrated below:

dict_you_want = {key: old_dict[key] for key in your_keys}

This approach has stable performance regardless of the size of the original dictionary, as it iterates through the keys in the specified list (your_keys) and fetches the corresponding values from the original dictionary.

Removing Unwanted Keys In-Place

The second method directly removes unwanted keys from the dictionary. It starts by identifying the keys to be removed:

unwanted = set(old_dict) - set(your_keys)

Next, a loop iterates over the unwanted keys and deletes them from the dictionary:

for unwanted_key in unwanted: del your_dict[unwanted_key]

This method has a slightly higher complexity than the first approach, as it iterates through all the keys in the original dictionary to locate the unwanted ones. However, it makes changes in-place, which may be more efficient in certain situations.

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