将函数应用于字典中 2 个键的每个可能组合

Question

I have a very big dictionary that has a word as a key and a vector as value, something like this

groceries = {'apples': array([1,2,1],dtype=float32),
             'bananas': array([1,3,4],dtype=float32),
             'potatoes': array([1,4,4],dtype=float32)}

Each vector is a representation of score for the grocery shop manager. I would like to find score for each possible combination of 2 keys. In this case a score for 'apples+bananas', score for 'bananas+potatoes', and score for 'apples+potatoes'.

So, I need to calculate all the possible sums of every key value with every other key value. I have a function that takes 2 variables:

def summing(u, v):
    return u+v

This function takes variables and sums their values, so the sum for 'apples+bananas' should be [2,5,5]

What would be a scaleable way to do it? I am trying to work with itertools, but I haven't used it before and it became very messy.

Answer 1

You can do:

sums = {key_combo: sum(groceries[k] for k in key_combo) for key_combo in itertools.combinations(groceries, 2)}

Explanation: itertools.combinations creates all combinations. The dictionary comprehension sums the values for each combination and assigns the results to a dictionary keyed with the combinations. Result is:

sums
{('apples', 'bananas'): array([2., 5., 5.], dtype=float32),
 ('apples', 'potatoes'): array([2., 6., 5.], dtype=float32),
 ('bananas', 'potatoes'): array([2., 7., 8.], dtype=float32)}

The function summing is not really necessary, as the numpy arrays know very well how to sum themselves.