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Find Common elements in three Lists using Sets - Python

Last Updated : 19 Feb, 2025

We are given three lists we need to find common elements in all three lists using sets. For example a = [1, 2, 3, 4], b = [2, 3, 5, 6] and c = [1, 2, 3, 7]. We need to find all common elements so that resultant output should be {2, 3}.

Using set.intersection()

set.intersection() method finds common elements between multiple sets by returning a new set containing only elements present in all sets. It efficiently identifies shared elements across any number of sets.

Python


 a = [1, 2, 3, 4]
b = [2, 3, 5, 6]
c = [1, 2, 3, 7]

# Convert lists to sets and find common elements
res = set(a).intersection(b, c)
print(f"Common elements: {res}")

Output

Common elements: {2, 3}

Explanation:

set(a).intersection(b, c) method converts the lists a, b, and c into sets and finds common elements shared among all three sets.
Resulting common elements are stored in the res set and printed as output.

Using & Operator

& operator performs a set intersection in Python returning a set containing only elements that are common to all sets involved. It is a shorthand for intersection() method providing same result.

Python


 a = [1, 2, 3, 4]
b = [2, 3, 5, 6]
c = [1, 2, 3, 7]

# Convert lists to sets and use the & operator
res = set(a) & set(b) & set(c)
print(f"Common elements: {res}")

Output

Common elements: {2, 3}

Explanation:

& operator is used to find intersection of the sets created from lists a, b, and c, returning only elements common to all sets.
Common elements are stored in res set and printed as result

Using Set Comprehension

Set comprehension allows the creation of a set by iterating over a sequence and applying a condition or transformation. It provides a concise way to build a set while filtering or modifying elements during iteration.

Python


 a = [1, 2, 3, 4]
b = [2, 3, 5, 6]
c = [1, 2, 3, 7]

# Set comprehension to find common elements
res = {x for x in a if x in b and x in c}
print(f"Common elements: {res}")

Output

Common elements: {2, 3}

Explanation:

Set comprehension {x for x in a if x in b and x in c} iterates over elements in a and adds them to the result if they are also present in both b and c.
Resulting common elements are stored in "res" set and printed as output.

Using filter() with lambda

filter() function with a lambda allows filtering elements from a sequence based on a condition. It returns an iterator with elements that satisfy condition specified by lambda function.

Python


 a = [1, 2, 3, 4]
b = [2, 3, 5, 6]
c = [1, 2, 3, 7]

# Filter common elements
res = set(filter(lambda x: x in b and x in c, a))
print(f"Common elements: {res}")

Output

Common elements: {2, 3}

Explanation:

filter() function with lambda expression iterates over elements in a keeping only those that are also present in both b and c.
Resulting common elements are converted to a set and printed as the output.

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