Compare two lists A, B in Python find all elements in A which correspond to the same number in B

Question

I want to compare two Python lists, \'A\' and \'B\' in such a manner that I can find all elements in A which correspond to the same number in B

Answer 1

A = [5, 7, 9, 12, 8, 16, 25]
B = [2, 1, 3, 2, 3, 1, 4]

Create a specific function that takes two lists (A, B) and a number (n) as arguments. Select all items in A that have the same list position as the items in B that are equivalent to n. zip is used to pair items from A and B with the same list position. This function uses a list comprehension to select the items from A.

>>> def f(A, B, n):
    return [a for a, b in zip(A,B) if b == n]

>>> f(A, B, 2)
[5, 12]
>>> 

The function could be written without a list comprehension:

def g(A, B, n):
    result = []
    for a, b in zip(A, B):
        if b == n:
            result.append(a)
    return result

Using fuctools.partial the list arguments can be fixed:

import functools
f_AB = functools.partial(f, A, B)

Then it could be used like this:

>>> f_AB(3)
[9, 8]

>>> numbers = [3, 4, 2]
>>> for n in numbers:
    print (n, f_AB(n))

(3, [9, 8])
(4, [25])
(2, [5, 12])
>>>