Get specific keys' values - Python

Our task is to retrieve values associated with specific keys from a dictionary. This is especially useful when we only need to access certain pieces of data rather than the entire dictionary. For example, suppose we have the following dictionary: d = {'name': 'John', 'age': 25, 'location': 'New York', 'job': 'Engineer'} if we need to get the values for the keys 'name' and 'job' then the output should be: {'name': 'John', 'job': 'Engineer'}

Using dictionary comprehension

We can use dictionary comprehension to achieve a more compact version of the loop method.

d = {'name': 'John', 'age': 25, 'location': 'New York', 'job': 'Engineer'}
filter_key = ['name', 'job']

res = {key: d[key] for key in filter_key if key in d}

print(res)

{'name': 'John', 'job': 'Engineer'}

Explanation:

• In this approach, dictionary comprehension is used to create the result dictionary by checking if each key in filter_key exists in d.
• If the key is found then we add it along with its value to the result dictionary.

Using a loop

We can iterate through the dictionary and check if the key exists then retrieve its value. This is a simple approach to get specific values based on the keys.

d = {'name': 'John', 'age': 25, 'location': 'New York', 'job': 'Engineer'}
filter_key = ['name', 'job']

res = {}
for key in filter_key:
    if key in d:
        res[key] = d[key]

print(res)

{'name': 'John', 'job': 'Engineer'}

Explanation: We define a list filter_key that contains the keys whose values we want to retrieve and then loop through each key in this list, if the key is present in the dictionary then we add the key-value pair to the result dictionary.

Using filter()

filter() function can also be used to filter out keys that we want to retrieve from the dictionary. It’s more functional in style and allows us to process the keys more flexibly.

d = {'name': 'John', 'age': 25, 'location': 'New York', 'job': 'Engineer'}
filter_key = ['name', 'job']

res = dict(filter(lambda item: item[0] in filter_key, d.items()))

print(res)  

{'name': 'John', 'job': 'Engineer'}

Explanation:

• d.items() gives us the key-value pairs of the dictionary and filter() function is used with a lambda function to check if the key is in the filter_key list.
• The result of filter() is converted back into a dictionary using dict().

Using map()

map() function can be used to apply a function to each item in an iterable allowing us to process the keys in the dictionary. We can then filter out the values for the specified keys.

d = {'name': 'John', 'age': 25, 'location': 'New York', 'job': 'Engineer'}
filter_key = ['name', 'job']

res = dict(map(lambda key: (key, d[key]) if key in d else (key, None), filter_key))

# Remove any keys that are not found in the dictionary
res = {key: val for key, val in res.items() if val is not None}

print(res) 

{'name': 'John', 'job': 'Engineer'}

Explanation:

• map() is used to apply a lambda function to each key in filter_key and if the key exists in d, the key-value pair is included in the result otherwise it returns None.
• After applying map() we filter out the None values using a dictionary comprehension to get the final result.