Python | Consecutive chunks Product

Some of the classical problems in the programming domain come from different categories and one among them is finding the product of subsets. This particular problem is also common when we need to compute the product and store consecutive group product values. Let’s try different approaches to this problem in Python language. 

Method #1 : Using list comprehension + loop

The list comprehension can be used to perform this particular task to filter out successive groups and the product explicit function can be used to get the product of the filtered solution. 

Python3

# Python3 code to demonstrate
# Consecutive chunks Product
# using list comprehension + loop

# getting Product


def prod(val):
    res = 1
    for ele in val:
        res *= ele
    return res


# Initializing list
test_list = [4, 7, 8, 10, 12, 15, 13, 17, 14]

# Printing original list
print("The original list : " + str(test_list))

# Consecutive chunks Product
# using list comprehension + loop
res = [prod(test_list[x: x + 3]) for x in range(0, len(test_list), 3)]

# Printing result
print("The chunked product list is : " + str(res))

Output : 

The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14]
The chunked product list is : [224, 1800, 3094]

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #2: Using loop + itertools.islice()

The task of slicing the list into chunks is done by islice method here and the conventional task of getting the product is done by the explicit product function as the above method. 

Python3

# Python3 code to demonstrate
# Consecutive chunks Product
# using itertools.islice() + loop

import itertools

# Getting Product
def prod(val):
    res = 1
    for ele in val:
        res *= ele
    return res

# Initializing list
test_list = [4, 7, 8, 10, 12, 15, 13, 17, 14]

# Printing original list
print("The original list : " + str(test_list))

# Consecutive chunks Product
# using itertools.islice() + loop
res = [prod(list(itertools.islice(test_list, i, i + 3)))
       for i in range(0, len(test_list), 3)]

# Printing result
print("The chunked product list is : " + str(res))

Output : 

The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14]
The chunked product list is : [224, 1800, 3094]

Time Complexity: O(n) where n is the number of elements in the list “test_list”. loop + itertools.islice() performs n number of operations.
Auxiliary Space: O(n), extra space is required where n is the number of elements in the list

Method #3 : Using reduce() + lambda

The inbuilt reduce function and the lambda function can also be used to perform this particular task. The reduce function is used to perform the product operation over the chunks and lambda is used to filter out the chunks.

Python3

# Python3 code to demonstrate
# Consecutive chunks Product
# using reduce() + lambda

# Getting Product
from functools import reduce

# Initializing list
test_list = [4, 7, 8, 10, 12, 15, 13, 17, 14]

# Printing original list
print("The original list : " + str(test_list))

# Consecutive chunks Product
# using reduce() + lambda
res = [reduce(lambda x, y: x * y, test_list[x: x + 3])
       for x in range(0, len(test_list), 3)]

# Printing result
print("The chunked product list is : " + str(res))

# This code is contributed by Edula Vinay Kumar Reddy

Output

The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14]
The chunked product list is : [224, 1800, 3094]

Time complexity: O(N)
Auxiliary Space: O(N)

Method #4: Using numpy.array_split() and numpy.prod()

Steps:

1. Import numpy library.
2. Initialize the input list.
3. Split the input list into chunks of 3 using numpy.array_split() function.
4. Calculate the product of each chunk using numpy.prod() function.
5. Store the result in a list.
6. Print the result.

Python3

import numpy as np

# Initializing list
test_list = [4, 7, 8, 10, 12, 15, 13, 17, 14]

# Printing original list
print("The original list : " + str(test_list))

# Consecutive chunks Product
# using numpy.array_split() and numpy.prod()
res = [np.prod(chunk)
       for chunk in np.array_split(test_list, len(test_list)//3)]

# Printing result
print("The chunked product list is : " + str(res))

Output

The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14]
The chunked product list is : [224, 1800, 3094]

Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), where n is the length of the input list.