Python | Custom Multiplication in list of lists

Last Updated : 25 Apr, 2019

Sometimes, when we are fed with the list of list, we need to multiply each of its element list with a particular element fed by the order in the other list. This particular problem is very specific but knowledge of it can be useful in such cases. Let’s discuss certain ways in which this can be done.

Method #1 : Using loops

This is the Naive and brute force method perform this particular task in which we run a loop to get all the elements and it’s nested components and multiply accordingly.

# Python3 code to demonstrate 
# Custom Multiplication in list of lists 
# Using loops 
  
# initializing list 
test_list = [[5, 6, 8], [7, 4, 3], [8, 10, 12]] 
  
# initializing multiply list  
mult_list = [10, 20, 30] 
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# printing multiply list 
print("The original multiply list : " + str(mult_list)) 
  
# using loops 
# Custom Multiplication in list of lists 
res = [[] for idx in range(len(test_list))] 
for i in range(len(test_list)): 
    for j in range(len(mult_list)): 
        res[i] += [mult_list[i] * test_list[i][j]] 
  
# print result 
print("The list after multiply : " + str(res)) 

Output :

The original list : [[5, 6, 8], [7, 4, 3], [8, 10, 12]]
The original multiply list : [10, 20, 30]
The list after multiply : [[50, 60, 80], [140, 80, 60], [240, 300, 360]]

Method #2 : Using list comprehension + enumerate()

This problem can also be solved in a shorter way using the power of enumerate function to get the indices and value of the container at one time. This is one-liner approach to solve this problem.

# Python3 code to demonstrate 
# Custom Multiplication in list of lists 
# Using list comprehension + enumerate() 
  
# initializing list 
test_list = [[5, 6, 8], [7, 4, 3], [8, 10, 12]] 
  
# initializing multiply list  
mult_list = [10, 20, 30] 
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# printing multiply list 
print("The original multiply list : " + str(mult_list)) 
  
# using list comprehension + enumerate() 
# Custom Multiplication in list of lists 
res = [[mult_list[i] * j for j in sub]  
       for i, sub in enumerate(test_list)] 
  
# print result 
print("The list after multiply : " + str(res)) 

Output :

The original list : [[5, 6, 8], [7, 4, 3], [8, 10, 12]]
The original multiply list : [10, 20, 30]
The list after multiply : [[50, 60, 80], [140, 80, 60], [240, 300, 360]]

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