Python | Multiply each element in a sublist by its index

Given a list of lists, the task is to multiply each element in a sublist by its index and return a summed list.

Given below are a few methods to solve the problem.

Method #1: Using Naive Method

# Python3 code to demonstrate 
# to multiply numbers with position 
# and add them to return num 
  
import numpy as np 
  
# initialising list 
ini_list = [[3, 4, 7], [ 6, 7, 8], [ 10, 7, 5], [ 11, 12, 13]] 
  
# printing initial_list 
print ("initial_list ", ini_list) 
  
res = [] 
# Using Naive Method 
for sub_list in ini_list: 
    sublistsum = 0
  
    for i, value in enumerate(sub_list): 
        sublistsum = sublistsum + i * value 
  
    res.append(sublistsum) 
  
# printing result 
print ("result", res) 

Output:

initial_list  [[3, 4, 7], [6, 7, 8], [10, 7, 5], [11, 12, 13]]
result [18, 23, 17, 38]

Method #2: Using List comprehension

# Python3 code to demonstrate 
# to multiply numbers with position 
# and add them to return num 
  
  
# initialising list 
ini_list = [[3, 4, 7], [ 6, 7, 8], [ 10, 7, 5], [ 11, 12, 13]] 
  
# printing initial_list 
print ("initial_list ", ini_list) 
  
# Using list comprehension 
res = [sum(i * j for i, j in enumerate(sublist))  
                         for sublist in ini_list] 
  
# printing result 
print ("result", res) 
             

Output:

initial_list  [[3, 4, 7], [6, 7, 8], [10, 7, 5], [11, 12, 13]]
result [18, 23, 17, 38]

Method #3: Using numpy

# Python3 code to demonstrate 
# to multiply numbers with position 
# and add them to return num 
  
import numpy as np 
  
# initialising list 
ini_list = [[3, 4, 7], [ 6, 7, 8], [ 10, 7, 5], [ 11, 12, 13]] 
  
# printing initial_list 
print ("initial_list ", ini_list) 
  
# Using numpy 
res = [np.arange(len(sublist)).dot(sublist) for sublist in ini_list] 
  
# printing result 
print ("result", res) 
              
             

Output:

initial_list  [[3, 4, 7], [6, 7, 8], [10, 7, 5], [11, 12, 13]]
result [18, 23, 17, 38]

My Personal Notes

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