在 python 中的特定索引之后，在嵌套列表中将元素相乘

Question

I have a nested list and I'd like to multiply all the elements, after a certain index, inside the list with each other. Like for example if my list is like this, (where all the elements inside (a1,f,g etc) are variables)

A=[[a1,a2,a3,f, g, g ],[b1, b2,b3, d, g, d]]

Id like for all the nested elements the third element to be multiplied together. So the output would be as a such,

A=[[a1,a2,a3,f*g**2], [b1, b2, b3, d**2*g]]

In addition, Im wondering if theres a way to separately multiply the remaining elements with the product at the end of each nested list,

A=[[a1*f*g**2,a2*f*g**2, a3*f*g**2], [b1*d**2*g, b2*d**2*g, b3*d**2*g]]

Im not really sure how to begin approaching this so any help is appreciated.

Answer 1

For the first part of the question, you can use a list comprehension to iterate over the sublists of A, followed by list indexing and the reduce function to compute what is required

import functools

A = [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11]]
B = [sublist[:3] + [functools.reduce(lambda x, y: x*y, sublist[3:])] for sublist in A]

print(B)

For the second part its better to do this with an explicit for loop so that the product of the end elements each sublist is only computed once

C = []
for sublist in A:
    end_product = functools.reduce(lambda x, y: x*y, sublist[3:])
    C.append([item*end_product for item in sublist[:3]])
print(C)

In the end this gives

A = [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11]]
B = [[1, 2, 3, 20], [6, 7, 8, 990]]
C = [[20, 40, 60], [5940, 6930, 7920]]

Answer 2

Stealing the other answer's data:

>>> from math import prod
>>> A = [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11]]
>>> for a in A:
        a[3:] = prod(a[3:]),

>>> A
[[1, 2, 3, 20], [6, 7, 8, 990]]

And with our without the above step:

>>> [[x * m for x in a[:3]] for a in A for m in [prod(a[3:])]]
[[20, 40, 60], [5940, 6930, 7920]]

Answer 3

Not sure if this is what you are looking for, but you can do it using a list comprehension and numpy:

from numpy import product

index = 5
A = [[5, 5, 2, 3, 4, 2, 1, 1, 2], [2, 4, 2, 3, 2, 4, 5, 7], [2, 3, 5, 6, 3, 5, 3, 2]]

result = [[b for i, b in enumerate(B) if i < index] + [product(B[index:])] for B in A]

print(result) # [[5, 5, 2, 3, 4, 4], [2, 4, 2, 3, 2, 140], [2, 3, 5, 6, 3, 30]]

and for your second question:

result2 = [[r * R[-1] for r in R[:-1]] for R in result]
print(result2) # [[20, 20, 8, 12, 16], [280, 560, 280, 420, 280], [60, 90, 150, 180, 90]]