Repeat Each Element K times in List - Python

Python | Increase list size by padding each element by N

Last Updated : 17 Apr, 2023

Given a list and an integer N, write a Python program to increase the size of the list by padding each element by N.

Examples:

Input : lst = [1, 2, 3]
        N = 3
Output : [1, 1, 1, 2, 2, 2, 3, 3, 3]

Input : lst = ['cats', 'dogs']
        N = 2
Output : ['cats', 'cats', 'dogs', 'dogs']

Approach #1 : List comprehension

Python3

# Python3 program to increase list size 
# by padding each element by N
 
def increaseSize(lst, N):
     
    return [el for el in lst for _ in range(N)]
         
# Driver code
lst = [1, 2, 3]
N = 3
print(increaseSize(lst, N))

Output:

[1, 1, 1, 2, 2, 2, 3, 3, 3]

Time Complexity: O(n), where n is the number of elements in the list
Auxiliary Space: O(1), constant space needed

Approach #2 : Using functools.reduce() method The reduce function apply a particular function passed in its argument to all of the list elements. Therefore, in this approach we apply a function on each element where it’s occurrence gets multiplied by N.

Python3

# Python3 program to increase list size 
# by padding each element by N
from functools import reduce
 
def increaseSize(lst, N):
     
    return reduce(lambda x, y: x + y, [[el]*N for el in lst])
         
# Driver code
lst = [1, 2, 3]
N = 3
print(increaseSize(lst, N))

Output:

[1, 1, 1, 2, 2, 2, 3, 3, 3]

Approach #3 : Using itertools.chain()

Python3

# Python3 program to increase list size 
# by padding each element by N
from itertools import chain
 
def increaseSize(lst, N):
     
    return list(chain(*([el]*N for el in lst)))
         
# Driver code
lst = [1, 2, 3]
N = 3
print(increaseSize(lst, N))

Output:

[1, 1, 1, 2, 2, 2, 3, 3, 3]

Approach #4 : Using * and extend() method

Initiate a for loop to access list elements
Repeat each list element by using * operator
And add repeated elements to output list(using extend())
Display output list

Python3

# Python3 program to increase list size
# by padding each element by N
 
lst = [1, 2, 3]
N = 3
x=[]
for i in lst:
    x.extend([i]*N)
print(x)

Output

[1, 1, 1, 2, 2, 2, 3, 3, 3]

Time Complexity : O(N)

Auxiliary Space : O(N)

Repeat Each Element K times in List - Python

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Smitha Dinesh Semwal

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