Given two lists, the task is to write a Python program to remove all the common elements of two lists.
Examples:
Input : list1 = [1, 2, 3, 4, 5]
list2 = [4, 5, 6, 7, 8,]
Output : list1 = [1, 2, 3]
list2 = [6, 7, 8]
Explanation: Lists after removing common elements of both the lists i.e, 4 and 5.
Input : list1 = [1, 2, 3]
list2 = [1, 2, 3]
Output : list1 = []
list2 = []
Explanation: They have all the elements in common in
between them.
Method 1: Using Remove() Method
The remove() method removes the first matching element (which is passed as an argument) from the list.
Python3
# Python program to remove common elements# in the two lists using remove methoddef remove_common(a, b): for i in a[:]: if i in b: a.remove(i) b.remove(i) print("list1 : ", a) print("list2 : ", b)if __name__ == "__main__": a = [1, 2, 3, 4, 5] b = [4, 5, 6, 7, 8] remove_common(a, b) |
list1 : [1, 2, 3] list2 : [6, 7, 8]
Time Complexity: O(n)
Auxiliary Space: O(1)
Method 2: Using List Comprehension
List comprehension gives a shorter syntax when you want to create a new list based on the elements of the existing list.
Python3
# Python program to remove common elements# in the two lists using list comprehensiondef remove_common(a, b): a, b = [i for i in a if i not in b], [j for j in b if j not in a] print("list1 : ", a) print("list2 : ", b)if __name__ == "__main__": a = [1, 2, 3, 4, 5] b = [4, 5, 6, 7, 8] remove_common(a, b) |
Time Complexity: O(n)
Space Complexity: O(n)
Method 3: Using Set’s difference operator
The difference operator – gets items in the first set but not in the second.
Python3
# Python program to remove common elements# in the two lists using Set’s difference# operatordef remove_common(a, b): a, b = list(set(a) - set(b)), list(set(b) - set(a)) print("list1 : ", a) print("list2 : ", b)if __name__ == "__main__": a = [1, 2, 3, 4, 5] b = [4, 5, 6, 7, 8] remove_common(a, b) |
list1 : [1, 2, 3] list2 : [8, 6, 7]
Method 4: Using Python Set difference() Method
The difference() method in python returns a set that contains the difference between two sets i.e, the returned set contains items that exist only in the first set and excludes elements present in both sets.
Python3
# Python program to remove common elements# in the two lists using Set difference()# methoddef remove_common(a, b): a, b = list(set(a).difference(b)), list(set(b).difference(a)) print("list1 : ", a) print("list2 : ", b)if __name__ == "__main__": a = [1, 2, 3, 4, 5] b = [4, 5, 6, 7, 8] remove_common(a, b) |
list1 : [1, 2, 3] list2 : [6, 7, 8]
Method #5: Using Counter() Function
Python3
from collections import Counter# Python program to remove common elements# in the two listsdef remove_common(a, b): freq1 = Counter(a) freq2 = Counter(b) for key in freq1: if key in freq2: a.remove(key) b.remove(key) print("list1 : ", a) print("list2 : ", b)if __name__ == "__main__": a = [1, 2, 3, 4, 5] b = [4, 5, 6, 7, 8] remove_common(a, b) |
list1 : [1, 2, 3] list2 : [6, 7, 8]
Method#6: Using filterfalse() from itertools
This method uses the filterfalse() function along with the __contains__() method of sets to create new lists that contain only elements that are not present in the other list
Python3
from itertools import filterfalsedef remove_common(a, b): a ,b= list(filterfalse(set(b).__contains__, a)), list(filterfalse(set(a).__contains__, b)) print("list1 : ", a) print("list2 : ", b)if __name__ == "__main__": a = [1, 2, 3, 4, 5] b = [4, 5, 6, 7, 8] remove_common(a, b) |
list1 : [1, 2, 3] list2 : [6, 7, 8]
Time complexity: O(N2).
Auxiliary space: O(1)
Another approach: Using set intersection
Python3
def remove_common(a, b): common = set(a) & set(b) a = [i for i in a if i not in common] b = [i for i in b if i not in common] print("list1 : ", a) print("list2 : ", b) a = [1, 2, 3, 4, 5]b = [4, 5, 6, 7, 8]remove_common(a, b) |
list1 : [1, 2, 3] list2 : [6, 7, 8]
Time Complexity: O(nlogn), where n is the number of elements in the list. The set intersection operation takes O(nlogn) time.
Auxiliary Space: O(n), where n is the number of elements in the list. The set requires O(n) space to store the elements.
Explanation:
We convert both the lists into sets and use the set intersection operation to find the common elements.
Then we use list comprehension to remove the common elements from both the lists and return the updated lists.
