Element-wise product of two 2-D lists

Question

I can\'t use Numpy or any other library function as this is a question I have to do, I have to define my own way.

I am writing a function that takes two lists (2 dimensi

Answer 1

You can zip the two lists in a list comprehension, then further zip the resulting sublists and then finally multiply the items:

list2 = [[5,2,9,3,7],[1,3,5,2,2]]
list1 = [[2,3,5,6,7],[5,2,9,3,7]]

result = [[a*b for a, b in zip(i, j)] for i, j in zip(list1, list2)]
print(result)
# [[10, 6, 45, 18, 49], [5, 6, 45, 6, 14]]

Should in case the lists/sublists do not have the same number of elements, itertools.izip_longest can be used to generate fill values such as an empty sublist for the smaller list, or 0 for the shorter sublist:

from itertools import izip_longest

list1 = [[2,3,5,6]]
list2 = [[5,2,9,3,7],[1,3,5,2,2]]
result = [[a*b for a, b in izip_longest(i, j, fillvalue=0)] 
               for i, j in izip_longest(list1, list2, fillvalue=[])]
print(result)
# [[10, 6, 45, 18, 0], [0, 0, 0, 0, 0]]

You may change the inner fillvalue from 0 to 1 to return the elements in the longer sublists as is, instead of a homogeneous 0.

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Reference:

List comprehensions