Python – First occurrence of one list in another
Given two lists, the task is to write a Python program to extract the first element that occurs in list 1 from list 2.
Examples:
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Input : test_list1 = [1, 6, 3, 7, 8, 9, 2], test_list2 = [4, 10, 8, 2, 0, 11]
Output : 8
Explanation : 8 is first element from list 2, that occurs in list 1, in 5th index.
Input : test_list1 = [1, 6, 3, 7, 8, 9, 2], test_list2 = [4, 10, 18, 12, 0, 11]
Output : None
Explanation : No element of list 2 found in list 1.
Approach : Using set() + next()
In this, initially, the check container is converted to set, and each element is checked using next() and generator expression. The next() function returns the first element matching, else if no match element is found, None is returned.
Python3
# Python3 code to demonstrate working of# First occurrence of one list in another# Using next() + set() # initializing liststest_list1 = [1, 6, 3, 7, 8, 9, 2]test_list2 = [4, 10, 8, 2, 0, 11] # printing original listsprint("The original list 1 is : " + str(test_list1))print("The original list 2 is : " + str(test_list2)) # converting test list to setstest_list2 = set(test_list2) # stops when 1st match element is foundres = next((ele for ele in test_list1 if ele in test_list2), None) # printing resultprint("First element in list 1 from 2 : " + str(res)) |
Output:
The original list 1 is : [1, 6, 3, 7, 8, 9, 2] The original list 2 is : [4, 10, 8, 2, 0, 11] First element in list 1 from 2 : 8
