[Tut] How to Intersect Multiple Sets in Python?

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How to Intersect Multiple Sets in Python?

To intersect multiple sets, stored in a list

Code:

l

, use the Python one-liner

Code:

l.pop().intersection(*l)

that takes the first set from the list, calls the

Code:

intersection()

method on it, and passes the remaining sets as arguments by unpacking them from the list.

A set is a unique collection of unordered elements. The intersection operation creates a new set that consists of the elements that exist in all sets.



So, let’s dive into the formal problem formulation, shall we?

Problem: Given a list or a collection of sets. How to jointhose sets using the intersection operation?

Example: You’ve got a list of sets

Code:

[{1, 2, 3}, {1, 4}, {2, 3, 5}]

and you want to calculate the intersection

Code:

{1}

.

Solution: To intersect a list of sets, use the following strategy:

• Get the first element from the list as a starting point. This assumes the list has at least one element.
  
  
• Call the
  Code:

  intersection()
  method on the first set object.
  
  
• Pass all sets as arguments into the
  Code:

  intersection()
  method by unpacking the list with the asterisk operator
  Code:

  *list
  .
  
  
• The result of the
  Code:

  intersection()
  method is a new set containing all elements that are in all of the sets.
  

Code: Here’s the one-liner codethat intersects a collection of sets.

Code:

# Create the list of sets lst = [{1, 2, 3}, {1, 4}, {1, 2, 3}] # One-Liner to intersect a list of sets print(lst[0].intersection(*lst))

The output of this code is the intersection of the three sets

Code:

{1, 2, 3}

,

Code:

{1, 4}

, and

Code:

{2, 3, 5}

. Only one element appears in all three sets:

Code:

{1}

If you love Python one-liners, check out my new book “Python One-Liners” (Amazon Link) that teaches you a thorough understanding of all single lines of Python code.

Try it yourself: Here’s the code in an interactive code shell that runs it in your browser:

https://trinket.io/embed/python/5eb34b02c7

Exercise: Change the code to calculate the union of the sets in the list!

Related video: A similar problem is to perform the union operation on a list of sets. In the following video, you can watch me explain how to union multiple sets in Python:



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