How flatten a list of lists one step

Question

I have a list of lists of tuples

A= [ [(1,2,3),(4,5,6)], [(7,8,9),(8,7,6),(5,4,3)],[(2,1,0),(1,3,5)] ]

The outer list can have any number of inner lists, the inner lists can have any number of tuples, a tuple always has 3 integers.

I want to generate all combination of tuples, one from each list:

[(1,2,3),(7,8,9),(2,1,0)]
[(1,2,3),(7,8,9),(1,3,5)]
[(1,2,3),(8,7,6),(2,1,0)]
...
[(4,5,6),(5,4,3),(1,3,5)]

A simple way to do it is to use a function similar to itertools.poduct() but it must be called like this

itertools.product([(1,2,3),(4,5,6)], [(7,8,9),(8,7,6),(5,4,3)],[(2,1,0),(1,3,5)])

i.e the outer list is removed. And I don't know how to do that. Is there a better way to generate all combinations of tuples?

How deep can the nested levels of lists be. Just 2, as in your example? — Kenan Banks, Nov 06 '09 at 16:34
Duplicate: http://stackoverflow.com/search?q=%5Bpython%5D+flatten, http://stackoverflow.com/questions/120886/python-idiom-to-chain-flatten-an-infinite-iterable-of-finite-iterables, http://stackoverflow.com/questions/406121/flattening-a-shallow-list-in-python — S.Lott, Nov 06 '09 at 16:38
@S Lott, related but not duplicates. (I thought so too, initially, the "flatten" keyword is misleading I think. Thought of editing title but didn't find a better expression; maybe "enumerate combinations"... — mjv, Nov 06 '09 at 16:45
Maybe wrong word, but thought it was about "flatten" when I wrote the question. No, it is not homework. I got my degree '83, been working sice then. But new with python. trying to solve a quiz in a swedish newspaper lead to all my questions so far. — lgwest, Nov 06 '09 at 16:59

score 10 · Accepted Answer · answered Nov 06 '09 at 16:38

10

itertools.product(*A)

For more details check the python tutorial

answered Nov 06 '09 at 16:38

Nadia Alramli

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score 2 · Answer 2 · answered Nov 06 '09 at 16:38

2

This works for your example, if there is only one level of nested lists (no lists of lists of lists):

itertools.product(*A)

answered Nov 06 '09 at 16:38

Kenan Banks

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score 2 · Answer 3 · edited Nov 30 '11 at 17:29

2

you can probably call itertools.product like so:

itertools.product(*A) # where A is your list of lists of tuples

This way it expands your list's elements into arguments for the function you are calling.

edited Nov 30 '11 at 17:29

Lesmana

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answered Nov 06 '09 at 16:38

Kevlar

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score 2 · Answer 4 · edited Nov 30 '11 at 17:31

2

Late to the party but ...

I'm new to python and come from a lisp background. This is what I came up with (check out the var names for lulz):

def flatten(lst):
    if lst:
        car,*cdr=lst
        if isinstance(car,(list)):
            if cdr: return flatten(car) + flatten(cdr)
            return flatten(car)
        if cdr: return [car] + flatten(cdr)
        return [car]

Seems to work. Test:

A = [ [(1,2,3),(4,5,6)], [(7,8,9),(8,7,6),(5,4,3)],[(2,1,0),(1,3,5)] ]

flatten(A)

Result:

[(1, 2, 3), (4, 5, 6), (7, 8, 9), (8, 7, 6), (5, 4, 3), (2, 1, 0), (1, 3, 5)]

Note: the line car,*cdr=lst only works in Python 3.0

edited Nov 30 '11 at 17:31

Lesmana

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answered Dec 21 '10 at 03:23

Michael Puckett

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-1 The statement ``car,*cdr=lst`` isn't even legal Python. There is no direct syntax in Python to split a list in its head and tail (sorry 'bout that). – ThomasH Apr 29 '11 at 08:32
@ThomasH: It *is* valid in Python 3. See http://www.python.org/dev/peps/pep-3132/. +1 to counteract needless downvote. – Steven Rumbalski Oct 25 '11 at 21:18
@StevenRumbalski Thanks for the pointer. I thought I was checking the Python 3 docs too, but obviously missed the `*target`. – ThomasH Oct 26 '11 at 16:41

score 1 · Answer 5 · answered Nov 06 '09 at 17:36

This is not exactly one step, but this would do what you want if for some reason you don't want to use the itertools solution:

def crossprod(listoflists):
    if len(listoflists) == 1:
        return listoflists
    else:
        result = []
        remaining_product = prod(listoflists[1:])
        for outertupe in listoflists[0]:
            for innercombo in remaining_product[0]:
                newcombo = [outertupe]
                newcombo.append(innercombo)
                result.append(newcombo)
        return result

score 1 · Answer 6 · edited Nov 30 '11 at 17:31

1

def flatten(A)
    answer = []
    for i in A:
        if type(i) == list:
            ans.extend(i)
        else:
            ans.append(i)
    return ans

edited Nov 30 '11 at 17:31

Lesmana

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answered Nov 08 '09 at 20:23

inspectorG4dget

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you need to fix your indentation. – SilentGhost Nov 08 '09 at 21:21
Terribly sorry for indentation errors. Turns out that copying code from my local IDE does not preserve proper indentation when I paste here – inspectorG4dget Nov 09 '09 at 02:03

score -1 · Answer 7 · edited Sep 05 '13 at 18:27

-1

This may also be achieved using list comprehension.

In [62]: A = [ [(1,2,3),(4,5,6)], [(7,8,9),(8,7,6),(5,4,3)],[(2,1,0),(1,3,5)] ]

In [63]: improved_list = [num for elem in A for num in elem]

In [64]: improved_list
Out[64]: [(1, 2, 3), (4, 5, 6), (7, 8, 9), (8, 7, 6), (5, 4, 3), (2, 1, 0), (1, 3, 5)]

edited Sep 05 '13 at 18:27

jcubic

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answered Oct 20 '12 at 00:10

ronak

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How flatten a list of lists one step

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