Python Itertools Add List for Every Combination

Question

I need to create every combination for list1, but add list2 to every combination of list1.

For example, this creates a combination for every value for list1:

list1 = ["a", "b" , "c"]
list2 = ["d", "e"]
list(itertools.combinations(list1, 2))
[('a', 'b'), ('a', 'c'), ('b', 'c')]

But I would like the result to be:

[('a', 'b', 'd', 'e'), ('a', 'c'', d', 'e'), ('b', 'c', 'd', 'e')]

I have tried these common approaches, but am getting undesired results:

list1 = ["a", "b" , "c"]
list2 = ["d", "e"]
print(list(itertools.combinations(list1, 2)).extend(list2))
None

print(list(itertools.combinations(list1, 2)) + list2)
[('a', 'b'), ('a', 'c'), ('b', 'c'), 'd', 'e']

print(list(itertools.combinations(list1, 2) + list2))
TypeError: unsupported operand type(s) for +: 'itertools.combinations' and 'list'

Any help would be appreciated. Thanks.

How would you do it if your intermediate result [('a', 'b'), ('a', 'c'), ('b', 'c')] didn't come from using itertools.combinations? — Karl Knechtel
– Karl Knechtel, Commented Apr 13, 2021 at 16:47

aminrd · Accepted Answer · 2021-04-13 16:43:38Z

1

You can first generate a tuple of size 2 combinations for each list separately, then compute the cartesian product of those to combination lists:

import itertools
list1 = ["a", "b" , "c"]
list2 = ["d", "e"]

iter1 = itertools.combinations(list1, 2)
iter2 = itertools.combinations(list2, 2)

# If you want to add a subset of size 2 from list 2: 
product = itertools.product(iter1, iter2)
answer = list(map(lambda x: (*x[0], *x[1]), product))
# [('a', 'b', 'd', 'e'), ('a', 'c', 'd', 'e'), ('b', 'c', 'd', 'e')]

However, if you want to add all elements of list2 you can use:

import itertools
list1 = ["a", "b" , "c"]
list2 = ["d", "e", "f"]

iter1 = itertools.combinations(list1, 2)

# If you want to add all elements of list2
product = itertools.product(iter1, [list2])
answer = list(map(lambda x: (*x[0], *x[1]), product))
# [('a', 'b', 'd', 'e', 'f'), ('a', 'c', 'd', 'e', 'f'), ('b', 'c', 'd', 'e', 'f')]

edited Apr 13, 2021 at 16:43

answered Apr 13, 2021 at 16:34

aminrd

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