python: how can I achieve a cartesian product of all the lists in a list?

Question

In particular I am looking if there is some cartesian_product() method built into python or a way to do this with itertools avoid having to write a nested multidimension loop.

for example I have the following

input = [
   [1], 
   [[2]], 
   [3], 
   [[a,b,c] , [[z,x,y]] , [d,f,g]], 
   4
]

expecting:

output = [
    [1,2,3,a,b,c,4]
    [1,2,3,z,x,y,4]
    [1,2,3,d,f,g,4]
]

The one particular challenge is that as in the above input list, an item can have any layer of lists, but it should be able to ignore all of those and still produce a flattened result.

Further, `input` is a keyword in python - do *not* use it as a variable name! — Nir Alfasi, Dec 07 '14 at 05:06
Related: http://stackoverflow.com/questions/533905/get-the-cartesian-product-of-a-series-of-lists-in-python — dmcc, Dec 07 '14 at 05:07

rorra · Answer 1 · 2014-12-07T05:25:47.357

3

input = [
    [1], 
    [[2]], 
    [3], 
    [['a','b','c'] , [['z','x','y']], ['d','f','g']], 
    4
]

input = map(lambda(x): x if isinstance(x, list) else [x], input)

import itertools
for element in itertools.product(*input):
    print element

edited Dec 07 '14 at 05:25

answered Dec 07 '14 at 04:58

rorra

9,593
3
39
61

You have the changed the input from int `4` to list `[4]`? – Tanveer Alam Dec 07 '14 at 05:02
Yes, in order to use itertools.product, just convert any scalar anto a list – rorra Dec 07 '14 at 05:08
Yes thats true but i think should have been included in code implimentation instead of manually updating the input ? – Tanveer Alam Dec 07 '14 at 05:11
could also use a list comprehension: input = [x if isinstance(x, list) else [x] for x in input] – Matt Adams Dec 07 '14 at 05:27
It doesn't print the expected output – Nir Alfasi Dec 07 '14 at 05:37

Nir Alfasi · Accepted Answer · 2014-12-07T17:43:55.830

To add on top of @rorra's answer, in order to print the results "flattened", add the following function:

def flat(l):
    def _flat(l, r):    
        if type(l) is not list:
            r.append(l)
        else:
            for i in l:
                r = r + flat(i)
        return r
    return _flat(l, [])

and then (rorra's code with a slight modification):

_input = [
    [1], 
    [[2]], 
    [3], 
    [['a','b','c'] , [['z','x','y']], ['d','f','g']], 
    4
]

_input = map(lambda(x): x if isinstance(x, list) else [x], _input)

import itertools
for element in itertools.product(*_input):
    print flat(list(element))  # this line was modified

OUTPUT

[1, 2, 3, 'a', 'b', 'c', 4]
[1, 2, 3, 'z', 'x', 'y', 4]
[1, 2, 3, 'd', 'f', 'g', 4]

python: how can I achieve a cartesian product of all the lists in a list?

2 Answers2