Python - Intersection of multiple lists

In this article, we will explore different approaches to find the intersection of multiple lists containing sub-lists. The intersection returns only the common sub-lists present in all input lists.

Using List Comprehension

The simplest approach uses list comprehension to check if each sub-list exists in all other lists ?

# initializing the lists
list_1 = [[1, 2], [3, 4], [5, 6]]
list_2 = [[3, 4], [7, 8]]

# finding the common items from both lists
result = [sub_list for sub_list in list_1 if sub_list in list_2]

# printing the result
print("Intersection using list comprehension:", result)

Intersection using list comprehension: [[3, 4]]

Using Set Intersection

Convert sub-lists to tuples (since lists are not hashable) and use set intersection for better performance ?

# initializing the lists
list_1 = [[1, 2], [3, 4], [5, 6]]
list_2 = [[3, 4], [7, 8]]

# converting each sub list to tuple for set support
tuple_1 = map(tuple, list_1)
tuple_2 = map(tuple, list_2)

# intersection using sets
result = list(map(list, set(tuple_1).intersection(tuple_2)))

# printing the result
print("Intersection using sets:", result)

Intersection using sets: [[3, 4]]

Intersection of Multiple Lists

For finding intersection among more than two lists, use the & operator or intersection() method ?

# initializing multiple lists
list_1 = [[1, 2], [3, 4], [5, 6]]
list_2 = [[3, 4], [5, 6]]
list_3 = [[3, 4], [9, 10]]

# convert to sets of tuples
set_1 = set(map(tuple, list_1))
set_2 = set(map(tuple, list_2))
set_3 = set(map(tuple, list_3))

# find intersection of all three sets
result = list(map(list, set_1 & set_2 & set_3))

print("Intersection of three lists:", result)

Intersection of three lists: [[3, 4]]

Using reduce() for Dynamic Lists

When dealing with a variable number of lists, use functools.reduce() ?

from functools import reduce

# list of lists to intersect
all_lists = [
    [[1, 2], [3, 4], [5, 6]],
    [[3, 4], [5, 6], [7, 8]], 
    [[3, 4], [9, 10]]
]

# convert each list to set of tuples and find intersection
sets = [set(map(tuple, lst)) for lst in all_lists]
result = list(map(list, reduce(set.intersection, sets)))

print("Dynamic intersection:", result)

Dynamic intersection: [[3, 4]]

Comparison

Conclusion

Use set intersection for better performance with large datasets. List comprehension works well for simple cases, while reduce() handles dynamic scenarios with multiple lists efficiently.