Python – Index Value repetition in List

Given a list of elements, The task is to write a Python program to repeat each index value as per the value in that index.

Input : test_list = [3, 0, 4, 2] 
Output : [0, 0, 0, 2, 2, 2, 2, 3, 3] 
Explanation : 0 is repeated 3 times as its index value is 3.

 Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.  

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course. And to begin with your Machine Learning Journey, join the Machine Learning - Basic Level Course

Input : test_list = [3, 4, 2] 
Output : [0, 0, 0, 1, 1, 1, 1, 2, 2] 
Explanation : 1 is repeated 4 times as its value is 4. 
 

Method #1 : Using list comprehension + enumerate()

In this, we perform task of repetition using * operator, and enumerate() is used to get indices along with values for repetition. List comprehension is used to iteration all the elements.

Output:

The original list is : [3, 0, 4, 2]
Constructed List : [0, 0, 0, 2, 2, 2, 2, 3, 3]

Method #2 : Using chain.from_iterable() + list comprehension

In this, we perform the last step of flattening of list using chain.from_iterable(). List comprehension performs the task of iteration of all the elements. 
 

Output:

The original list is : [3, 0, 4, 2]
Constructed List : [0, 0, 0, 2, 2, 2, 2, 3, 3]