How to apply itertools.product to a nested list in Python

Question

Let say I have a nested list of string

lst = [['a'], ['b', 'c'], ['d', ['e', 'f']]]

I want to generate all possible combination from the nested list to something like this:

new_lst = [['a', 'b', 'd'],
           ['a', 'b', 'e', 'f'],
           ['a', 'c', 'd'],
           ['a', 'c', 'e', 'f']]

I have found some question that may related to my question. how to produce a nested list from two lists in python However, my question is more complicated issue.

I would flatten the list and then use sets. `itertools` probably has a method that does this automatically. — Luke McPuke, Jan 30 '18 at 06:20
possible duplicate of https://stackoverflow.com/questions/8371887/making-all-possible-combinations-of-a-list-in-python — Midhun Mohan, Jan 30 '18 at 06:22
@MidhunMohan in that question they are taking combinations from a simple list while OP is asking product of his particular nested list — Vikas Periyadath, Jan 30 '18 at 06:25
@JonKiparsky, I don't believe you *fixed* the title but diluted it. I believe the correct title would be more like, "How to apply itertools.product to a nested list in Python". — cdlane, Jan 30 '18 at 07:03

Vivek Kalyanarangan · Accepted Answer · 2018-01-30T06:48:56.187

5

Here's what will do the trick -

import itertools
lst = [['a'], ['b', 'c'], ['d', ['e', 'f']]]
outp = list(itertools.product(*lst))
out = []
for i in outp:
    temp = []
    for j in i:
        if isinstance(j, list):
            for k in j:
                temp.append(k)
        else:
            temp.append(j)
    out.append(temp)
print(out)

Start off by forming the output materials using itertools.product and then simply formatting it in a way that the nested lists are flattened out.

Output

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

edited Jan 30 '18 at 06:48

answered Jan 30 '18 at 06:36

Vivek Kalyanarangan

8,951
1
23
42

1

Good answer .try to avoid that `print(here)` statement – Vikas Periyadath Jan 30 '18 at 06:46
1

hmm strange why this was down voted, its a perfectly working solution. – RoadRunner Jan 30 '18 at 06:47
@VikasDamodar took care of it. Thanks! – Vivek Kalyanarangan Jan 30 '18 at 06:47
@RoadRunner Wondering the same :-) – Vivek Kalyanarangan Jan 30 '18 at 06:48

Paul Panzer · Answer 2 · 2018-01-30T07:10:26.320

3

Similar to @VivekKalyanarangan but with a proper flattener:

>>> def flatten(nl):
...     for e in nl:
...         if isinstance(e, str):
...             yield e
...             continue
...         try:
...             yield from flatten(e)
...         except TypeError:
...             yield e
... 

>>> lst = [['a'], ['b', 'c'], ['d', ['e', 'f']]]
>>> 
>>> list(map(list, map(flatten, itertools.product(*lst))))
[['a', 'b', 'd'], ['a', 'b', 'e', 'f'], ['a', 'c', 'd'], ['a', 'c', 'e', 'f']]

edited Jan 30 '18 at 07:10

answered Jan 30 '18 at 06:44

Paul Panzer

51,835
3
54
99

If I change the data to be `lst = [[1], [2, 3], [4, [5, 6]]]`, this solution still works. So what is the `isinstance(e, str)` really doing for you? – cdlane Jan 30 '18 at 07:21

score 1 · Answer 3 · answered Mar 09 '19 at 22:58

You can use chain.from_iterable() to flattern results:

from itertools import product, chain

lst = [['a'], ['b', 'c'], ['d', ['e', 'f']]]

[list(chain.from_iterable(i)) for i in product(*lst)]
# [['a', 'b', 'd'], ['a', 'b', 'e', 'f'], ['a', 'c', 'd'], ['a', 'c', 'e', 'f']]

score -1 · Answer 4 · answered Mar 09 '19 at 22:30

Another way by using list comprehension

>>> ls = [['a'], ['b', 'c'], ['d', ['e', 'f']]]
>>> res = ['']
>>> for elem in ls:
...     res = [list(j) + list(e) for j in res for e in elem]
... 
>>> res
[['a', 'b', 'd'], ['a', 'b', 'e', 'f'], ['a', 'c', 'd'], ['a', 'c', 'e', 'f']]

score -2 · Answer 5 · answered Jan 30 '18 at 06:40

Is this what you're looking for?

from itertools import permutations
lst = [['a'], ['b', 'c'], ['d', ['e', 'f']]]
list(permutations(lst))

Otherwise, give this a try:

lst = ['a','b','c','d','e','f']
list(permutations(lst))   ##will return all possible combos

How to apply itertools.product to a nested list in Python

5 Answers5