Python Program to Extract Elements from a List in a Set

When it is required to extract elements from a list that exist in a set, a simple 'for' loop with membership checking can be used. This technique filters the list to keep only elements that are present in the target set.

Method 1: Using For Loop

Below is a demonstration using a basic for loop with conditional checking ?

my_list = [5, 7, 2, 7, 2, 4, 9, 8, 8]

print("The list is:")
print(my_list)

search_set = {6, 2, 8}
print("The search set is:")
print(search_set)

my_result = []
for element in my_list:
    if element in search_set:
        my_result.append(element)

print("The result is:")
print(my_result)

The list is:
[5, 7, 2, 7, 2, 4, 9, 8, 8]
The search set is:
{8, 2, 6}
The result is:
[2, 2, 8, 8]

Method 2: Using List Comprehension

A more concise approach using list comprehension ?

my_list = [5, 7, 2, 7, 2, 4, 9, 8, 8]
search_set = {6, 2, 8}

result = [element for element in my_list if element in search_set]

print("Original list:", my_list)
print("Search set:", search_set)
print("Filtered result:", result)

Original list: [5, 7, 2, 7, 2, 4, 9, 8, 8]
Search set: {8, 2, 6}
Filtered result: [2, 2, 8, 8]

Method 3: Using filter() Function

Using the built-in filter() function with a lambda expression ?

my_list = [5, 7, 2, 7, 2, 4, 9, 8, 8]
search_set = {6, 2, 8}

result = list(filter(lambda x: x in search_set, my_list))

print("Original list:", my_list)
print("Search set:", search_set)
print("Filtered result:", result)

Original list: [5, 7, 2, 7, 2, 4, 9, 8, 8]
Search set: {8, 2, 6}
Filtered result: [2, 2, 8, 8]

How It Works

• A list with duplicate elements is defined and displayed on the console.

• A set containing target elements is created for membership testing.

• Each method iterates through the list and checks if elements exist in the set.

• Matching elements are collected while preserving their original order and duplicates.

• The `in` operator provides O(1) average lookup time for sets, making it efficient.

Comparison

Conclusion

Use list comprehension for concise and readable code when extracting elements from a list based on set membership. The `in` operator with sets provides efficient O(1) lookup time, making these approaches suitable for large datasets.