Python | Check if two lists have any element in common

Checking if two lists share any common elements is a frequent requirement in Python. It can be efficiently handled using different methods depending on the use case. In this article, we explore some simple and effective ways to perform this check.

Using set Intersection

Set intersection uses Python's built-in set data structure to efficiently identify common elements between two lists. The intersection operation directly returns a set containing elements that are present in both lists.

a = [1, 2, 3, 4]
b = [3, 5, 6]

# Check for common elements
common = set(a) & set(b)

print(bool(common))  

True

Explanation:

• Converts both lists to sets which allowing fast membership testing.
• Performs the & (intersection) operation to find common elements.
• Returns True if any elements overlap.

Let's explore some more methods and see how we can check if two lists have any element in common.

Using any()

This method combines a generator expression with Python’s built-in any() to streamline the process. It stops as soon as it finds the first match, making it more efficient than looping through all elements.

a = [1, 2, 3, 4]
b = [3, 5, 6]

# Check for common elements using any()
common = any(x in a for x in b)

print(common)

True

Explanation:

• The generator expression checks if any element from the first list exists in the second list.
• any() returns True if at least one common element is found.

Using filter()

filter() function can also be employed by applying a condition that checks if an element from one list exists in another list. It works by iterating over the first list and including only the elements that satisfy the condition (i.e., they are also present in the second list).

a = [1, 2, 3, 4]
b = [3, 5, 6]

# Check for common elements using filter()
common = list(filter(lambda x: x in b, a))

print(bool(common))

True

Explanation:

• It Filters the elements of 'a' based on their presence in 'b'.
• Converts the filter object to a list to determine if there are common elements.

Using a Loop

This method uses a loop and involves iterating through one list and checking if each element exists in the second list. This method typically uses the in keyword inside the loop to verify membership.

a = [1, 2, 3, 4]
b = [3, 5, 6]

# Check for common elements using a loop
common = False
for x in a:
    if x in b:
        common = True
        break

print(common)

True

Explanation:

• Here, the loop iterates through the first list and checks if any element exists in the second list.
• It Stops immediately when a common element is found.