Merge sublist with each item of list

Question

I have a list of lists and I need to join them together with each item of list. See example below:

my_list = [1, [2, 3], [4, 5]]

Expected result:

['1', '1.2', '1.3', '1.2.4', '1.2.5', '1.3.4', '1.3.5']

I tried to write the logic but one or other items are always missing.

Asked By: varun22486

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Source

Answer 1

You can use the itertools.product function from the itertools module to generate all possible combinations of items from the lists, then use a list comprehension to join the items together using the desired format.

Here is an example of how you can use it:

import itertools

my_list = [1, [2, 3], [4, 5]]

combinations = list(itertools.product(*my_list))
result = [".".join(map(str, x)) for x in combinations]

print(result)

This will output:

['1.2.4', '1.2.5', '1.3.4', '1.3.5']

Note that this assumes that all of the elements of the list are lists, if you have integer or string mixed in your list, you need to convert them to string before joining them.

Answered By: Emir Çoban

Answer 2

def join_lists(result, prefix, items):
    if not items:
        result.append('.'.join(map(str, prefix)))
    else:
        for i, item in enumerate(items[0]):
            join_lists(result, prefix + [item], items[1:])
        join_lists(result, prefix, items[1:])

my_list = [1, [2, 3], [4, 5]]
result = []
join_lists(result, [1], my_list)
print(result)

will produce:

Output: ['1', '1.2', '1.3', '1.2.4', '1.2.5', '1.3.4', '1.3.5']

Answered By: Seppe Willems

Answer 3

You could do this:

import itertools
my_list = [1, [2, 3], [4, 5]]

# First convert each scalar into list 
my_list = [[e] if not isinstance(e, list) else e for e in my_list]

# and then each element into str
my_list = [list(map(str, e)) for e in my_list]

# Then initialize a result list and keep extending with product of the result 
# with the next element in my_list
t = my_list[0]
out = []
out.extend(t)
for lst in my_list[1:]:
    t = list(map('.'.join, itertools.product(t, lst)))
    out.extend(t)
print(out)

['1', '1.2', '1.3', '1.2.4', '1.2.5', '1.3.4', '1.3.5']

# for the input my_list = [[1,2],3,[4,5]]
my_list = [[1,2],3,[4,5]]
print(out)
['1', '2', '1.3', '2.3', '1.3.4', '1.3.5', '2.3.4', '2.3.5']

Answered By: SomeDude

Answer 4

Using itertools.accumulate:

from itertools import accumulate, product

# ensure sub-items are lists
def as_lst(x):
    return x if isinstance(x, list) else [str(x)]

out = [str(e) for l in (accumulate(map(as_lst, my_list),
                                   lambda *x: ['.'.join(map(str, y))
                                               for y in product(*x)])
                       )
       for e in as_lst(l)]

print(out)

Output:

['1', '1.2', '1.3', '1.2.4', '1.2.5', '1.3.4', '1.3.5']

Output for my_list=[[1,2],3,[4,5]]:

['1', '2', '1.3', '2.3', '1.3.4', '1.3.5', '2.3.4', '2.3.5']

Answered By: mozway

Merge sublist with each item of list

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