Possible combinations of key and values without duplicates

Question

I am trying to get all the unique combinations (not permutations as order is not important) of keys (str) and corresponding values (str) from the dictionary (without duplicates) in a readable form.

items_dict = {
    'item1': {'value1', 'value2', 'value3'},
    'item2': {'value1', 'value4'},
    'item3': {'value5', 'value2', 'value6', 'value1'}
}

I put the values in sets so that one could union them. Maybe using dictionary and sets is not the right way of resolving it.

I tried with:

comb = combinations((items_dict.items()), 2)

but then got tuples of keys and values:

(('item2': {'value1', 'value4'}), ('item1': {'val ...

I need expected results to looks like this to identify combinations of keys and corresponding values separated:

'item1', 'item2': {'value1', 'value2', 'value3', 'value4'}
'item2', 'item 3': {'value5', 'value2', 'value6', 'value1', 'value4'}
'item3', 'item1': {'value1', 'value2', 'value3', 'value5', 'value6'}

Answer 1

So you need the itertools.combinations result of the keys, then the set combines of those keys' values.

import itertools
from typing import Mapping, Tuple, Any

def get_combinations(d: Mapping[Any, set]) -> Mapping[Tuple[Any, Any], set]:
    """Combine keys into pairs and merge values together.

    >>> d = {1: {1, 2}, 2: {3, 4}, 3: {1, 4}}
    >>> get_combinations(d)
    {(1, 2): {1, 2, 3, 4}, (1, 3): {1, 2, 4}, (2, 3): {1, 3, 4}}
    """

    key_combos = itertools.combinations(d.keys(), 2)

    result = {key_combo: set.union(*(d[key] for key in key_combo)) for key_combo in key_combos}
    return result

Answer 2

you could pack that in a dict-comprehension:

from itertools import combinations

items_dict = {
    'item1': {'value1', 'value2', 'value3'},
    'item2': {'value1', 'value4'},
    'item3': {'value5', 'value2', 'value6', 'value1'}
}

res = {(key1, key2):  value1 | value2 
       for (key1, value1), (key2, value2) in combinations(items_dict.items(), r=2)}
 # {('item1', 'item2'): {'value4', 'value3', 'value2', 'value1'}, 
 #  ('item1', 'item3'): {'value5', 'value3', 'value6', 'value2', 'value1'}, 
 #  ('item2', 'item3'): {'value4', 'value5', 'value6', 'value2', 'value1'}}

it might be even more useful to use a frozenset as key of your new dictionary:

res = {frozenset((key1, key2)):  value1 | value2 
       for (key1, value1), (key2, value2) in combinations(items_dict.items(), r=2)}
# {frozenset({'item1', 'item2'}): {'value2', 'value4', 'value1', 'value3'}, 
#  frozenset({'item1', 'item3'}): {'value2', 'value1', 'value3', 'value5', 'value6'}, 
#  frozenset({'item3', 'item2'}): {'value2', 'value4', 'value1', 'value5', 'value6'}}

that way you can access the values without knowing the order that combinations produced:

# those will be the same
res[frozenset(('item3', 'item1'))]
res[frozenset(('item1', 'item3'))]

here is how you could adapt that if you need combinations of more than 2 items:

res = {frozenset(k[0] for k in kv): set.union(*(v[1] for v in kv)) 
       for kv in combinations(items_dict.items(), r=2)}