Python | Intersection of two nested list

This particular article aims at achieving the task of intersecting two list, in which each element is in itself a list. This is also a useful utility as this kind of task can come in life of programmer if he is in the world of development. Lets discuss some ways to achieve this task.

Method 1 : Naive Method
This is the simplest method to achieve this task and uses the brute force approach of executing a loop and to check if one list contains similar list as of the other list.

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# Python 3 code to demonstrate 
# find intersection of nested list
# using naive method
  
# initializing lists
test_list1 = [ [1, 2], [3, 4], [5, 6] ]
test_list2 = [ [3, 4], [5, 7], [1, 2] ]
  
# printing both lists 
print ("The original list 1 : " + str(test_list1))
print ("The original list 2 : " + str(test_list2))
  
# using naive method 
# to get list intersection
res_list = []
for i in test_list1:
    if i in test_list2:
        res_list.append(i)
  
# printing the intersection 
print ("The intersection of two lists is : " + str(res_list))

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Output :



The original list 1 : [[1, 2], [3, 4], [5, 6]]
The original list 2 : [[3, 4], [5, 7], [1, 2]]
The intersection of two lists is : [[1, 2], [3, 4]]

Method 2 : Using list comprehension
We can perform the similar task as discussed above in comparatively less no. of lines. But the method is similar as above just uses list comprehension approach to perform the task.

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# Python 3 code to demonstrate 
# find intersection of nested list
# using list comprehension
  
# initializing lists
test_list1 = [ [1, 2], [3, 4], [5, 6] ]
test_list2 = [ [3, 4], [5, 7], [1, 2] ]
  
# printing both lists 
print ("The original list 1 : " + str(test_list1))
print ("The original list 2 : " + str(test_list2))
  
# using list comprehension
# to get list intersection
res_list = [i for i in test_list1 if i in test_list2]
  
# printing the intersection 
print ("The intersection of two lists is : " + str(res_list))

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Output :

The original list 1 : [[1, 2], [3, 4], [5, 6]]
The original list 2 : [[3, 4], [5, 7], [1, 2]]
The intersection of two lists is : [[1, 2], [3, 4]]

Method 3 : Using set() + map() and &
The most efficient and recommended method to perform this task is using the combination of set() and map() to achieve it. Firstly converting inner lists to tuples using map, and outer lists to set, use of & operator can perform the set intersection and hence perform this task. Further if it is required to get in lists of list fashion, we can convert outer and inner containers back to list using map().

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# Python 3 code to demonstrate 
# find intersection of nested list
# using map() + set() + &
  
# initializing lists
test_list1 = [ [1, 2], [3, 4], [5, 6] ]
test_list2 = [ [3, 4], [5, 7], [1, 2] ]
  
# printing both lists 
print ("The original list 1 : " + str(test_list1))
print ("The original list 2 : " + str(test_list2))
  
# using map() + set() + &
# to get list intersection
res_set = set(map(tuple, test_list1)) & set(map(tuple, test_list2))
res_list = list(map(list, res_set))
  
# printing the intersection 
print ("The intersection of two lists is : " + str(res_list))

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Output :

The original list 1 : [[1, 2], [3, 4], [5, 6]]
The original list 2 : [[3, 4], [5, 7], [1, 2]]
The intersection of two lists is : [[1, 2], [3, 4]]


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