Combining two lists ( so [['a', 'b'], ['c', 'd']] = ['ac', 'ad', 'bc', 'bd] ) the pythonic way

Question

Given a list of lists such as:

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

Result should be:

['ace', 'ade', 'bce', 'bde']

The nested lists will be different lengths. Order must be maintained -- i.e. first letter must come from first list, second letter from second list, etc.

Here is my current, recursive solution:

def combine_letters(l)
    if len(l) == 0: 
        return l[0]
    temp = [x + y for x in l[0] for y in l[1]] 
    new = [temp] + l[2:]
    return combine_letters(new)

However, I feel like there should be a quick, maybe even one line, way to do this, possible using the reduce function. Any thoughts?

Thank you!

Edit: this is not exactly analogous to the linked question. First, it is for a arbitrarily large number of sublists. Second, it returns strings rather than tuples.

score 5 · Accepted Answer · answered Dec 05 '14 at 00:55

>>> L = [['a', 'b'], ['c', 'd'], ['e']]
>>> import itertools
>>> list(itertools.product(*L))
[('a', 'c', 'e'), ('a', 'd', 'e'), ('b', 'c', 'e'), ('b', 'd', 'e')]
>>> list(''.join(tup) for tup in list(itertools.product(*L)))
['ace', 'ade', 'bce', 'bde']

Combining two lists ( so [['a', 'b'], ['c', 'd']] = ['ac', 'ad', 'bc', 'bd] ) the pythonic way

1 Answers1