sets of combinations between two lists in python

Question

I have two lists of 12 items and I want to compute the following:

-12 sets of combinations of the items so each item have been combined with each other on the other list after the 12 times. Simplified example:

list_a = ['a','b','c','d']
list_b = ['blue','green','red','white']

The 4 sets of combinations would be:

[
[['a','blue'], ['b','green'], ['c','red'], ['d','white']],
[['a','white'], ['b','red'], ['c','green'], ['d','blue']],
[['a','green'], ['b','white'], ['c','blue'], ['d','red']],
[['a','red'], ['b','blue'], ['c','white'], ['d','green']]
]

I tried with itertools but I get out of memory errors

Edit: I need to get the set with unique combinations. Not ['a','blue'],['a','green']...

More like in the example that I posted earlier

Please provide the itertools code? Since you need 144 combinations, it seems something wrong to have OOM error — Chris
– Chris, Commented Oct 7, 2022 at 1:28
import itertools; list(itertools.product(list_a, list_b)) will do what you want — Kid Charlamagne
– Kid Charlamagne, Commented Oct 7, 2022 at 1:31

chrille0313 · Accepted Answer · 2022-10-07 02:35:42Z

0

As far as I've understood what you are trying to achieve, I came up with the following algorithm. You generate every rotation of b_list and then map each value at index i in a_list to the corresponding value at index i in b_list. Here is the implementation of the explained approach:

list_a = ['a', 'b', 'c', 'd']
list_b = ['blue', 'green', 'red', 'white']

combinations = []

for start in range(len(list_b)):
    combination = []

    for i in range(len(list_b)):
        combination.append([list_a[i], list_b[(start + i) % len(list_b)]])

    combinations.append(combination)
    
print(combinations)

edited Oct 7, 2022 at 2:35

answered Oct 7, 2022 at 1:30

chrille0313

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6 Comments

thunder27 Over a year ago

Thanks for your response. With this I get ['a', 'blue'], ['a', 'green'], ['a', 'red'] while I need every item to repeat only once in every set of combinations

chrille0313 Over a year ago

I don't really understand what you mean. Does the order of the combinations matter?

chrille0313 Over a year ago

Oh, I think I'm starting to get what you want to achieve. Do you only want the rotations of the combinations or do all the permutations matter?

chrille0313 Over a year ago

I will edit my answer with an updated one.

thunder27 Over a year ago

Think as if 12 brothers had 12 shirts to share. They want to organise so in 12 days everyone would have worn every shirt once.

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Jubick · Accepted Answer · 2022-10-07 02:48:03Z

-1

def combine(list_a, list_b):
res = []
for i in range(len(list_a)):
    res.append([])
    for j in range(len(list_b)):
        res[-1].append([list_a[j], list_b[(j + i) % len(list_b)]])
return res

list_a = ['a', 'b', 'c', 'd']
list_b = ['blue', 'green', 'red', 'white']
print(combine(list_a, list_b))

I have this output:

[[['a', 'blue'], ['b', 'green'], ['c', 'red'], ['d', 'white']], 
[['a', 'green'], ['b', 'red'], ['c', 'white'], ['d', 'blue']], 
[['a', 'red'], ['b', 'white'], ['c', 'blue'], ['d', 'green']], 
[['a', 'white'], ['b', 'blue'], ['c', 'green'], ['d', 'red']]]

answered Oct 7, 2022 at 2:48

Jubick

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1 Comment

chrille0313 Over a year ago

This is a duplicate answer to mine with no added insight.

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