Python – Extract element from list succeeded by K
Given a list, extract the elements which are having K as the next element.
Input : test_list = [2, 3, 5, 7, 8, 5, 3, 5], K = 3
Output : [2, 5]
Explanation : Elements before 3 are 2, 5.Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.
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Input : test_list = [2, 3, 5, 7, 8, 5, 3, 8], K = 8
Output : [7, 3]
Explanation : Elements before 8 are 7, 3.
Method #1: Using loop
In this, we iterate the list and look for each K, and extract the element preceding it.
Python3
# Python3 code to demonstrate working of# Extract elements succeeded by K# Using loop # initializing listtest_list = [2, 3, 5, 7, 8, 5, 3, 5] # printing original listprint("The original list is : " + str(test_list)) # initializing KK = 5 # Using loop to extract elements succeeded by Kres = []for idx in range(len(test_list) - 1): # checking for succession if test_list[idx + 1] == K: res.append(test_list[idx]) # printing resultprint("Extracted elements list : " + str(res)) |
The original list is : [2, 3, 5, 7, 8, 5, 3, 5] Extracted elements list : [3, 8, 3]
Method #2: Using list comprehension
Another way to solve this question, in this, we use list comprehension as shorthand to solve the problem of getting elements.
Python3
# Python3 code to demonstrate working of# Extract elements succeeded by K# Using list comprehension # initializing listtest_list = [2, 3, 5, 7, 8, 5, 3, 5] # printing original listprint("The original list is : " + str(test_list)) # initializing KK = 5 # List comprehension used as shorthandres = [test_list[idx] for idx in range(len(test_list) - 1) if test_list[idx + 1] == K] # printing resultprint("Extracted elements list : " + str(res)) |
The original list is : [2, 3, 5, 7, 8, 5, 3, 5] Extracted elements list : [3, 8, 3]
