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:
{1}
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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?
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