Python | Print all the common elements of two lists
Given two lists, print all the common elements of two lists.
Examples:
Input : list1 = [1, 2, 3, 4, 5] list2 = [5, 6, 7, 8, 9] Output : {5} Explanation: The common elements of both the lists are 3 and 4 Input : list1 = [1, 2, 3, 4, 5] list2 = [6, 7, 8, 9] Output : No common elements Explanation: They do not have any elements in common in between themMethod 1:Using Set’s & property
Convert the lists to sets and then print set1&set2. set1&set2 returns the common elements set, where set1 is the list1 and set2 is the list2.
Below is the Python3 implementation of the above approach:
# Python program to find the common elements
# in two lists
def common_member(a, b):
a_set = set(a)
b_set = set(b)
if (a_set & b_set):
print(a_set & b_set)
else:
print("No common elements")
a = [1, 2, 3, 4, 5]
b = [5, 6, 7, 8, 9]
common_member(a, b)
a = [1, 2, 3, 4, 5]
b = [6, 7, 8, 9]
common_member(a, b)
|
Output:
{5} No common elementsMethod 2:Using Set’s intersection property
Convert the list to set by conversion. Use the intersection function to check if both sets have any elements in common. If they have many elements in common, then print the intersection of both sets.
Below is the Python3 implementation of the above approach:
# Python program to find common elements in
# both sets using intersection function in
# sets
# function
def common_member(a, b):
a_set = set(a)
b_set = set(b)
# check length
if len(a_set.intersection(b_set)) > 0:
return(a_set.intersection(b_set))
else:
return("no common elements")
a = [1, 2, 3, 4, 5]
b = [5, 6, 7, 8, 9]
print(common_member(a, b))
a =[1, 2, 3, 4, 5]
b =[6, 7, 8, 9]
print(common_member(a, b))
|
Output:
{5} No common elementsPython | Intersection of two lists
Intersection of two list means we need to take all those elements which are common to both of the initial lists and store them into another list. Now there are various ways in Python, through which we can perform the Intersection of the lists.
Examples:
Method 1:
This is the simplest method where we haven’t used any built-in functions.
# Python program to illustrate the intersection
# of two lists in most simple way
def intersection(lst1, lst2):
lst3 = [value for value in lst1 if value in lst2]
return lst3
# Driver Code
lst1 = [4, 9, 1, 17, 11, 26, 28, 54, 69]
lst2 = [9, 9, 74, 21, 45, 11, 63, 28, 26]
print(intersection(lst1, lst2))
|
Output:
Method 2:
This method includes the use of set() method.
# Python program to illustrate the intersection
# of two lists using set() method
def intersection(lst1, lst2):
return list(set(lst1) & set(lst2))
# Driver Code
lst1 = [15, 9, 10, 56, 23, 78, 5, 4, 9]
lst2 = [9, 4, 5, 36, 47, 26, 10, 45, 87]
print(intersection(lst1, lst2))
|
Output:
Method 3:
In this method we set() the larger list and then use the built-in function called intersection() to compute the intersected list. intersection() is a first-class part of set.
# Python program to illustrate the intersection
# of two lists using set() and intersection()
def Intersection(lst1, lst2):
return set(lst1).intersection(lst2)
# Driver Code
lst1 = [ 4, 9, 1, 17, 11, 26, 28, 28, 26, 66, 91]
lst2 = [9, 9, 74, 21, 45, 11, 63]
print(Intersection(lst1, lst2))
|
Output:
Method 4:
By the use of this hybrid method the complexity of the program falls to O(n). This is an efficient way of doing the following program.
# Python program to illustrate the intersection
# of two lists
def intersection(lst1, lst2):
# Use of hybrid method
temp = set(lst2)
lst3 = [value for value in lst1 if value in temp]
return lst3
# Driver Code
lst1 = [9, 9, 74, 21, 45, 11, 63]
lst2 = [4, 9, 1, 17, 11, 26, 28, 28, 26, 66, 91]
print(intersection(lst1, lst2))
|
Output:
Method 5:
This is the where the intersection is performed over sub-lists inside other lists. Here we have used the concept of filter().
# Python program to illustrate the intersection
# of two lists, sublists and use of filter()
def intersection(lst1, lst2):
lst3 = [list(filter(lambda x: x in lst1, sublist)) for sublist in lst2]
return lst3
# Driver Code
lst1 = [1, 6, 7, 10, 13, 28, 32, 41, 58, 63]
lst2 = [[13, 17, 18, 21, 32], [7, 11, 13, 14, 28], [1, 5, 6, 8, 15, 16]]
print(intersection(lst1, lst2))
|
Working: The filter part takes each sublist’s item and checks to see if it is in the source list. The list comprehension is executed for each sublist in list2.
Output:
Find the common elements in two lists in Python
In this tutorial, We are going to learn how to find the common elements in two lists in Python.
To find the common list from two lists, we have to store the common elements in the third variable. There are various methods to find and store the common elements from two lists.