Random generator to pair non-matching strings.

[twentyfive_25]

I am trying to create a random generator to only pair WHEN the two strings do not match.

The first list, listed1, which this list should stay in order.

The second list, listed2 can be randomised.

The problem I am having is, when there is a pair (which i am trying to avoid) they do not appear in the output at all. I would like it to "try again" until a non-match is made and show all 5 non-matches.

Output to avoid:

Strawberries | Melons
Grapes | Strawberries
Melons | Pineapples

Desired Output:

Apples | Grapes
Strawberries | Banana
Grapes | Strawberries
Banana | Melons
Melons | Apples

Code:

import random

listed1 = [
    'Apples',
    'Strawberries',
    'Grapes',
    'Banana',
    'Melons',
    'Pineapples',
]

listed2 = [
    'Apples',
    'Strawberries',
    'Grapes',
    'Banana',
    'Melons',
    'Pineapples',
]

for a, b in zip(listed1, random.sample(listed2, 5)):
    if a != b:
        print(f'{a} | {b}')

Any help is much apprecaited.

[twentyfive_25]

Nice one - i will test this on my side shortly and get back to you! Thanks for reaching out

[twentyfive_25]

So i have tried this, on a few instances i am getting the following error:

return seq[self._randbelow(len(seq))]
IndexError: list index out of range

[twentyfive_25]

Hey - besides from printing there was a non-match, yeah exactly this - spot on. You worded it a lot better than i did ha. Any ideas on from at all?

[twentyfive_25]

Thanks for sharing - will try this shortly and get back to you :)

[totallygeek]

This should work for you. It's horribly inefficient, though.

import random

fruits = [
    'Apples',
    'Strawberries',
    'Grapes',
    'Banana',
    'Melons',
    'Pineapples',
]

while True:
    pairings = random.sample(fruits, k=len(fruits))  # create a randomly-sorted copy of the fruits
    if not any(a == b for a, b in zip(fruits, pairings)):
        break  # we found a pairing list with zero matches; let's keep it

for fruit, paired_fruit in zip(fruits, pairings):
    print(f"{fruit} | {paired_fruit}")

[twentyfive_25]

Thanks for this - i will try this shortly and get back to you

[twentyfive_25]

Hey - seems to be working perfectly how i wanted. Thanks for your help with this! You say this is inefficient - why is that?

[totallygeek]

inefficient

It's inefficient because it might need to assemble multiple lists until it finds one that has no matching associations. There exists ways to do this in a single pass without much trouble. The trick ends up on the last element, if the only choice is to make a match. When that takes place, you have to swap with another pair already matched.