Python: Get a list of elements that exist in both lists
Python List: Exercise - 226 with Solution
Write a Python program to get a list of elements that exist in both lists, after applying the provided function to each list element of both.
- Create a set, using map() to apply fn to each element in b.
- Use a list comprehension in combination with fn on a to only keep values contained in both lists.
Sample Solution-1:
Applying a given function:
Python Code:
def intersection_by(a, b, fn):
_b = set(map(fn, b))
return [item for item in a if fn(item) in _b]
from math import floor
print(intersection_by([2.1, 1.2], [2.3, 3.4], floor))
Sample Output:
[2.1]
Flowchart:

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Sample Solution-2:
Without applying any function:
Use a list comprehension on x to only keep values contained in both lists.
Python Code:
def similarity(x, y):
return [item for item in x if item in y]
nums1 = [1, 2, 3, 4]
nums2 = [1, 2, 4, 5]
print("Original lists:")
print(nums1)
print(nums2)
print("\nList of elements that exist in both lists:")
print(similarity(nums1, nums2))
Sample Output:
Original lists: [1, 2, 3, 4] [1, 2, 4, 5] List of elements that exist in both lists: [1, 2, 4]
Flowchart:

Visualize Python code execution:
The following tool visualize what the computer is doing step-by-step as it executes the said program:
Sample Solution-3:
Without applying any function:
- Create a set from a and b.
- Use the built-in set operator & to only keep values contained in both sets, then transform the set back into a list.
Python Code:
def common_elements(l1, l2):
_l1, _l2 = set(l1), set(l2)
return list(_l1 & _l2)
nums1 = [1, 2, 3, 4]
nums2 = [1, 2, 4, 5]
print("Original lists:")
print(nums1)
print(nums2)
print("\nList of elements that exist in both lists:")
print(common_elements(nums1, nums2))
Sample Output:
Original lists: [1, 2, 3, 4] [1, 2, 4, 5] List of elements that exist in both lists: [1, 2, 4]
Flowchart:

Visualize Python code execution:
The following tool visualize what the computer is doing step-by-step as it executes the said program:
Python Code Editor:
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Previous: Write a Python program to retrieve the value of the nested key indicated by the given selector list from a dictionary or list.
Next: Write a Python program to get the symmetric difference between two lists, after applying the provided function to each list element of both.
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Python: Tips of the Day
Given a predicate function, fn, and a prop string, this curried function will then take an object to inspect by calling the property and passing it to the predicate:
Example:
def tips_check_prop(fn, prop): return lambda obj: fn(obj[prop]) check_age = tips_check_prop(lambda x: x >= 25, 'age') user = {'name': 'Owen', 'age': 25} print(check_age(user))
Output:
True
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