To intersect multiple sets, stored in a list l, use the Python one-liner l.pop().intersection(*l) that takes the first set from the list, calls the 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 join those sets using the intersection operation?
Example: You’ve got a list of sets [{1, 2, 3}, {1, 4}, {2, 3, 5}] and you want to calculate the intersection {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
intersection()method on the first set object. - Pass all sets as arguments into the
intersection()method by unpacking the list with the asterisk operator*list. - The result of the
intersection()method is a new set containing all elements that are in all of the sets.
Code: Here’s the one-liner code that intersects a collection of sets.
# 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 {1, 2, 3}, {1, 4}, and {2, 3, 5}. Only one element appears in all three sets:
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Try it yourself: Here’s the code in an interactive code shell that runs it in your browser:
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:
Where to Go From Here?
Enough theory, let’s get some practice!
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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.