lists permutation in python

Question

I have the following lists:

list1 = [ 'A','B','C']
list2 = [ '1', '2' ]

Trying to generate a new list of tuples with the following desired result:

[(A1),(A2),(A1,B1),(A1,B2),(A2,B1),(A2,B2),(A1,B1,C1),(A2,B1,C1)...]

Each tuple will eventully be used to write a single line in an output file.
Note that:

In each tuple, each letter from list1, if defined, must be defined after the preceding letters. for example, if 'B' is defined in a tuple then 'A' must be in the tuple as well and prior to 'B'. tuple (A1,C1) is not desired since 'B' is not defined as well.
Tuples must be unique.
list1 & list2 are just an example and may vary in length.

I tried playing around with itertools, specifically with, product, permutations, combinations for quite some time. I can't seem to pull it off and I don't even have some code worth sharing.

Martijn Pieters · Accepted Answer · 2014-01-07T15:12:12.833

2

Take successive larger slices of list1, and use products of products:

from itertools import product

elements = []
for letter in list1:
    elements.append([''.join(c) for c in product(letter, list2)])
    for combo in product(*elements):
        print combo

The elements list is grown each loop, adding another set of letter + numbers list to produce products from.

This produces:

>>> elements = []
>>> for letter in list1:
...     elements.append([''.join(c) for c in product(letter, list2)])
...     for combo in product(*elements):
...         print combo
... 

('A1',)
('A2',)
('A1', 'B1')
('A1', 'B2')
('A2', 'B1')
('A2', 'B2')
('A1', 'B1', 'C1')
('A1', 'B1', 'C2')
('A1', 'B2', 'C1')
('A1', 'B2', 'C2')
('A2', 'B1', 'C1')
('A2', 'B1', 'C2')
('A2', 'B2', 'C1')
('A2', 'B2', 'C2')

edited Jan 07 '14 at 15:12

answered Jan 07 '14 at 14:58

Martijn Pieters

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I missed a step here. :-) – Martijn Pieters Jan 07 '14 at 15:00
@Nabla: there, fixed it. – Martijn Pieters Jan 07 '14 at 15:04
Yes, I see that now, looking into it. – Martijn Pieters Jan 07 '14 at 15:06
Hi, 10x for the solution. however there is a glitch in it. if you change list1, to [A,bb,C] the result are not as excepted. your solution assumes list1 contain item of length 1 only. – idanshmu Jan 07 '14 at 15:33
@idanshmu: put square brackets around the `letter`: `product([letter], list2)`. – Martijn Pieters Jan 07 '14 at 15:35
yap. did the trick. the only thing left to do is understand how the hell you did it. 10x again. – idanshmu Jan 07 '14 at 15:37

score 1 · Answer 2 · answered Jan 07 '14 at 15:14

1

What about this:

from itertools import product

output = []
for z in [list1[:n+1] for n in range(len(list1))]:
   for y in product(list2, repeat=len(z)):
      output.append(tuple(''.join(u) for u in zip(z, y)))

print(output)

answered Jan 07 '14 at 15:14

richsilv

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Great man. works perfectly. I would have accepted both answer if I could. Martijn Pieters just beat you to it. – idanshmu Jan 07 '14 at 15:40
Not for the first time! – richsilv Jan 07 '14 at 15:40

lists permutation in python

2 Answers2