Create all possible combinations of lists of different sizes in numpy-CodePudding

I want to create a numpy array with all possible combinations of items from multiple lists of different sizes:

a = [1, 2] 
b = [3, 4]
c = [5, 6, 7] 
d = [8, 9, 10]

In each combination, I want 2 elements. I don't want any duplicates, and I don't want items from the same list to mix together.

I can get all such combinations with 3 elements with np.array(np.meshgrid(a, b, c, d)).T.reshape(-1,3) but I need pairs, not triplets. Doing np.array(np.meshgrid(a, b, c, d)).T.reshape(-1,2) doesn't work because it just cuts off one column of the original array.

Any ideas on how to achieve this?

CodePudding user response：

Similar to Olvin Roght's comment, but if you put your sublists in a list you can do:

>>>> ls = [[1,2],[3,4],[5,6,7],[8,9,10]]
>>>> [item for cmb in combinations(ls, 2) for item in product(*cmb)]
[(1, 3), (1, 4), (2, 3), (2, 4), (1, 5), (1, 6), (1, 7), (2, 5), (2, 6), (2, 7), (1, 8), (1, 9), (1, 10), (2, 8), (2, 9), (2, 10), (3, 5), (3, 6), (3, 7), (4, 5), (4, 6), (4, 7), (3, 8), (3, 9), (3, 10), (4, 8), (4, 9), (4, 10), (5, 8), (5, 9), (5, 10), (6, 8), (6, 9), (6, 10), (7, 8), (7, 9), (7, 10)]

CodePudding user response：

So Itertools is great for this. The first thing you want to do is conjoin your list into a single iterable list (list of lists). The first step is to get all combinations of list.

from itertools import combinations, product

a = [1, 2] 
b = [3, 4]
c = [5, 6, 7] 
d = [8, 9, 10]
total = [a,b,c,d]
for item in combinations(total, 2):
    print(item)

which returns

([1, 2], [3, 4])
([1, 2], [5, 6, 7])
([1, 2], [8, 9, 10])
([3, 4], [5, 6, 7])
([3, 4], [8, 9, 10])
([5, 6, 7], [8, 9, 10])

The you can simply iterate over the individual lists as below

from itertools import combinations

a = [1, 2] 
b = [3, 4]
c = [5, 6, 7] 
d = [8, 9, 10]
total = [a,b,c,d]
for item in combinations(total, 2):
    for sub_item in item[0]:
        for second_sub_item in item[1]:
            print(sub_item, second_sub_item)

print out is