Python | Custom length Matrix

Sometimes, we need to initialize a matrix in Python of variable length from the list containing elements. In this article, we will discuss the variable length method initialization and certain shorthands to do so. Let’s discuss certain ways to perform this.

Method #1 : Using zip() + list comprehension
The zip function combined with the list comprehension can help to achieve this particular task. The zip function can help to zip the counter list with the element list and list comprehension does the work of construction of matrix.

# Python3 code to demonstrate   
# Custom length Matrix  
# using zip() + list comprehension 
  
# initializing list 
test_list = ['a', 'b', 'c'] 
  
# initializing counter list  
counter_list = [1, 4, 2] 
  
# printing original list  
print ("The original list is : " + str(test_list)) 
  
# printing counter list  
print ("The counter list is : " + str(counter_list)) 
  
# using zip() + list comprehension 
# Custom length Matrix  
res = [[i] * j for i, j in zip(test_list, counter_list)] 
  
# printing result 
print ("The custom length matrix is : " + str(res)) 

Output :

The original list is : ['a', 'b', 'c']
The counter list is : [1, 4, 2]
The custom length matrix is : [['a'], ['b', 'b', 'b', 'b'], ['c', 'c']]

Method #2 : Using map() + mul operator
This particular problem can also be solved using the inbuilt mul operator which performs multiplication of liked index elements and map function performs the task of formation of matrix.

# Python3 code to demonstrate   
# Custom length Matrix  
# using map() + mul operator 
from operator import mul 
  
# initializing list 
test_list = ['a', 'b', 'c'] 
  
# initializing counter list  
counter_list = [1, 4, 2] 
  
# printing original list  
print ("The original list is : " + str(test_list)) 
  
# printing counter list  
print ("The counter list is : " + str(counter_list)) 
  
# using map() + mul operator 
# Custom length Matrix  
res = list(map(mul, [['a'], ['b'], ['c']], counter_list)) 
  
# printing result 
print ("The custom length matrix is : " + str(res)) 

Output :

The original list is : ['a', 'b', 'c']
The counter list is : [1, 4, 2]
The custom length matrix is : [['a'], ['b', 'b', 'b', 'b'], ['c', 'c']]

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