Intersection() of Sets in Python

September 22, 2023

Intersection() of a Set

The intersection() of two or more sets returns a set that contains all common items from all the sets. The result set contains a distinct element that is, the item that is present in all sets, the result will contain only one appearance of this item. ∩ the symbol denotes the intersection of sets.

PYTHON PROGRAM TO UNION AND INTERSECTION OF TWO SORTED LIST

Intersection of sets in Python

In Python, you can find the intersection of sets using the intersection() method or the & operator. The intersection of two sets contains only the elements that are common to both sets. 

Let us understand this concept with an example, suppose there are two sets A and B, we have to find A ∩ B.

A = { 1 , 2, 3, 4, 5 }

B = { 1, 3, 5, 7, 9 }

A ∩ B = { 1, 3, 5 }

Python Set Intersection()

Syntax :


set1.intersection(set2,set3,…)

The parameter can be only one or more. You can compare as many sets as you like. Separate each set with a comma.

Return Type :

The intersection() method returns a new set with all the common elements from the set and all other sets (passed as an argument).

If the argument is not passed to the intersection(), it returns a shallow copy of the set.

Using the & operator

Run 
#intersection of sets using & operator

#example 1

set1 = {'P', 'Y', 'T', 'H', 'O', 'N' }
set2 = {'C', 'O', 'D', 'I', 'N', 'G' }
print( set1 & set2 )

#example 2
A = { 2, 4, 6, 8, 10, 11, 12 }
B = { 3, 6, 9, 12, 15 }
C = { 4, 8, 12, 16 }
print( A & B & C )
Output :

{'N', 'O'}
{12}

Sets in Python

set add() in python

Python Set union()

Python Set difference() Method

Python Set symmetric_difference()

Using intersection() function

Run 
#intersection of sets using intersection() method

#example 1
set1 = {'P', 'Y', 'T', 'H', 'O', 'N' }
set2 = {'C', 'O', 'D', 'I', 'N', 'G' }
print(set1.intersection(set2) )

#example 2
A = { 2, 4, 6, 8 , 10, 12, 14, 16, 18, 20 }
B = { 3, 6, 9, 12, 15, 18, 21, 24, 27, 30 }
C = { 4, 8, 12, 16, 20, 24, 28, 32, 36, 40 }
print( A.intersection(B,C) )
Output :

{'N', 'O'}
{12}

Intersection of three sets

A , B, C are three sets having some elements.

Approach:
  • First Calculate intersection of two sets (A ∩ B) and store it in any set say X.
  • Then find intersection of X and the third set i.e. (X ∩ C).

A ∩ B ∩ C  =  (A ∩ B) ∩ C  =  A ∩ (B ∩ C)  =  (A ∩ C) ∩ B

Run

#intersection of three sets

A = { 2, 4, 6, 8 , 10, 12, 14, 16, 18, 20 }
B = { 3, 6, 9, 12, 15, 18, 21, 24, 27, 30 }
C = { 4, 8, 12, 16, 20, 24, 28, 32, 36, 40 }

#A & B
x=A.intersection(B)
print("A intersectionb B : ",x)

#A & C
y=A.intersection(C)
print("A intersectionb C : ",y)

#B & C
z=B.intersection(C)
print("B intersectionb C : ",z)

#( A & B ) & C = A & B & C
print("( A & B ) & C  : ",x.intersection(C))

#( A & C ) & B = A & B & C
print("( A & C ) & B  : ",y.intersection(B))

# A & ( B  & C ) = A & B & C
print("A & ( B  & C ) : ",z.intersection(A))

#A & B & C
print( "A & B & C     : ",A.intersection(B,C) )
Output :

A intersectionb B :  {18, 12, 6}
A intersectionb C :  {4, 8, 12, 16, 20}
B intersectionb C :  {24, 12}

(A & B) & C :  {12}
(A & C) & B :  {12}
A & (B & C) :  {12}
A & B & C   :  {12}

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