Python Set Intersection

Python Set Intersection Methods with Best Examples

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Set in Python is one of the fundamental data structures that store sequential elements.

It is represented by curly brackets and separates every element with a comma.

Sets are mutable and unordered, which means that indexing in a set is not accurate.

What is Python set intersection?

The set intersection in Python can be described as the production of a new set composed of the elements shared by both sets.

In simple words, it returns a set that contains elements that are common to all the sets.

Additional information from the Python official documentation, set intersection() returns a new set with elements common to the set and all others.

Example:

Set1 = {1, 2, 3, 4, 5}
Set2 = {4, 5, 6, 7, 8, 9, 10}

# compute intersection between Set1 and Set2
print(Set1.intersection(Set2))

Illustration of the above example:

Output:

{4, 5}

Syntax of set intersection()

Below is the syntax:

set1.intersection(set2, set3, set4...)

Parameters of set intersection()

Set intersection() accepts an arbitrary number of arguments.

Return value from set intersection()

Set intersection() returns a new set that contains the common to all the given sets.

There are two methods to perform an intersection in a set:

  • The intersection() method
  • The & method.

Python set intersection() method:

Using the set intersection() operator in Python.

Example 1: Working with two sets intersection()

The intersection of two sets using string elements.

Set1 = {"P", "R", "I", "N", "C", "E"}
Set2 = {"C", "E", "S", "A", "R"}

print(Set1.intersection(Set2))

Illustration of the above example program:

Output:

{'E', 'C', 'R'}

Example 2: Working with three sets intersection()

The calculation of the intersection of three sets.

Set1 = {1, 2, 3, 4, 5, 6}
Set2 = {2, 4, 6, 8, 10, 12}
Set3 = {3, 6, 9, 12, 15, 18}

# intersection between set 1 and set 2
print(Set1.intersection(Set2))

# intersection between set 2 and set 3
print(Set2.intersection(Set3))

# intersection between set 3 and set 1
print(Set3.intersection(Set1))

# intersection of all the sets
print("Intersection of All sets:",Set1.intersection(Set2,Set3))

Illustration of the above example program:

Output:

Set1 and Set2: {2, 4, 6}
Set2 and Set3: {12, 6}
Set3 and Set1: {3, 6}
Intersection of All sets: {6}

Example 3: Working with four sets intersection()

The calculation of the intersection of four sets.

Set1 = {1, 2, 3, 4, 5, 6}
Set2 = {2, 4, 6, 8, 10, 12}
Set3 = {3, 6, 9, 12, 15, 18}
Set4 = {4, 8, 12, 16, 20, 24}

print(Set1.intersection(Set4))
print(Set2.intersection(Set4))
print(Set3.intersection(Set4))
print(Set1.intersection(Set2, Set3, Set4))

Illustration of the above example program:

Output:

{4}
{8, 4, 12}
{12}
set()

Python set intersection using & operator method

You can also find the intersection of sets using & operator.

Example:

Set1 = {1, 2, 3, 4, 5, 6}
Set2 = {2, 4, 6, 8, 10, 12}
Set3 = {3, 6, 9, 12, 15, 18}
Set4 = {4, 8, 12, 16, 20, 24}

print(Set1 & Set3)
print(Set1 & Set4)
print(Set1 & Set2 & Set3)
print(Set1 & Set2 & Set3 & Set4)

Illustration of the above example program:

Output:

{3, 6}
{4}
{6}
set()

How do you calculate the intersection between two sets in Python?

To calculate the intersection between the two sets, we have to use the len() method.

Example:

set1 = {1, 2, 3}
set2 = {3, 4, 5}

result = len(set(set1 & set2))

      
print("The number of common elements in both sets:",result)

Output:

The number of common elements in both sets: 1

Python set intersection complexity

Tested the time complexity of the set intersection, according to them.

The runtime complexity of the set.intersection() method on a set with n elements and a set argument with m elements is O(min(n, m)) because you need to check for the smaller set whether each of its elements is a member of the larger set.

Checking membership is O(1), so the runtime complexity is O(min(n, m)) * O(1) = O(min(n, m)).

Summary

After reading this article, we should now have a good understanding of how to use the intersection() method and set intersection & operator method.

You are now ready to use it in an actual program.

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