How to flatmap list of lists of lists of tuples in Python?

Question

I am using Calendar and recieve list of lists of lists of tuples from it

calendar.Calendar.yeardays2calendar(calendar.Calendar(), year, 1))

Output is:

[[[[(0, 0), (0, 1), (0, 2), (1, 3), (2, 4), (3, 5), (4, 6)], [(5, 0), (6, 1), (7, 2), (8, 3), (9, 4), (10, 5), (11, 6)], [(12, 0), (13, 1),...

I want to flat map it to simple tuples list saving their order. What is the best way to do map list of any deepness into plain list in python 2.7?

Example of what I want:

[(0, 0), (0, 1), (0, 2), (1, 3), (2, 4), (3, 5), (4, 6),(5, 0), (6, 1), (7, 2), (8, 3), (9, 4), (10, 5), (11, 6), (12, 0), (13, 1)...

Tryied code from other questions - didn't help. Sorry for silly questions, I'm new to python

UPD I tried functions from here python list comprehensions; compressing a list of lists? - didn't help

What was the other code you tried , and what was the issue with that ? — Anand S Kumar, Aug 22 '15 at 12:17
I didn't get errors, but it couldn't flatten my list, because all examples were for list of lists like [[1,3,4],[4,3],[3]] which is not my case — maxpovver, Aug 22 '15 at 12:18

Sven Marnach · Accepted Answer · 2015-08-22T12:32:45.067

4

Python has a function to flatten one nesting level. It goes by the unfortunate name itertools.chain.from_iterable(). If you apply it three times, it will flatten three levels:

import itertools
flatten1 = itertools.chain.from_iterable
flattened_data = flatten1(flatten1(flatten1(your_data)))
for a, b in flattened_data:
    # whatever

More generically, a function that flattens n levels would be

def flatten_n(n, iterable):
    for x in reduce(apply, [itertools.chain.from_iterable] * n, iterable):
        yield x

A function that recursively flattens all lists could look like this:

def flatten_lists(a):
    if isinstance(a, list):
        for b in a:
            for x in flatten_lists(b):
                yield x
    else:
        yield a

edited Aug 22 '15 at 12:32

answered Aug 22 '15 at 12:21

Sven Marnach

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I understand this as I am not new to programming, only to python :) But what if it would be deeper? Are there any better ways to that? That work on any deepness – maxpovver Aug 22 '15 at 12:23
@maxpovver: It depends on what you want. If you just flatten arbitrary iterables, you will also flatten out your tuples. You could write a recursive function that flattens all lists, if this is what you want. You could also write a generic function that takes the number of levels you want to flatten as an argument. You can do all that, but you didn't ask for it. :) – Sven Marnach Aug 22 '15 at 12:25
If I get it right, your code won't help on this: [ [ [1,2,3], [1,2,3] ], [ [1,2,3], [1,2,3, [1, 2, 3] ] ]. – maxpovver Aug 22 '15 at 12:25
@maxpovver: No, it doesn't, since this isn't what you asked for. – Sven Marnach Aug 22 '15 at 12:26
tried you code, it loses items order – maxpovver Aug 22 '15 at 12:30
@maxpovver: I don't think so. Can you provide an example? – Sven Marnach Aug 22 '15 at 12:33
there was error in my tuples using @SvenMarnach – maxpovver Aug 22 '15 at 12:36
@maxpovver The third solution I gave is a more memory-efficient alternative to karthikr's answer. – Sven Marnach Aug 22 '15 at 12:42
that's why I accepted yours, thanks! – maxpovver Aug 22 '15 at 12:56

score 3 · Answer 2 · edited May 23 '17 at 12:22

Try this:

def flatten(x):
    if isinstance(x, list):
        return [a for i in x for a in flatten(i)]
    else:
        return [x]

This answer is similar to this: https://stackoverflow.com/a/2158522/1628832 but checking for the specific list type instead of an iterable.

For optimization, memory efficiency, etc.. you can use yield operation too.

Demo

>>> year = 2015
>>> x = calendar.Calendar.yeardays2calendar(calendar.Calendar(), year, 1)
>>> flatten(x)
[(0, 0), (0, 1), (0, 2), (1, 3), (2, 4), (3, 5), (4, 6), (5, 0), (6, 1), (7, 2), (8, 3), (9, 4), (10, 5), (11, 6), (12, 0), (13, 1), (14, 2), (15, 3), (16, 4), (17, 5), (18, 6), (19, 0), (20, 1), (21, 2), (22, 3), (23, 4), (24, 5), (25, 6), ...]

score 0 · Answer 3 · answered Aug 22 '15 at 12:54

If you are using Python 2, the following one liner solution will currently work:

import compiler, itertools

lpairs = [[[[(0, 0), (0, 1), (0, 2), (1, 3), (2, 4), (3, 5), (4, 6)], [(5, 0), (6, 1), (7, 2), (8, 3), (9, 4), (10, 5), (11, 6)], [(12, 0), (13, 1)]]]]

print [(x,y) for x,y in itertools.izip(*[iter(compiler.ast.flatten(lpairs))]*2)]

Gives:

[(0, 0), (0, 1), (0, 2), (1, 3), (2, 4), (3, 5), (4, 6), (5, 0), (6, 1), (7, 2), (8, 3), (9, 4), (10, 5), (11, 6), (12, 0), (13, 1)]

Note, the Python compiler module has been deprecated.

How to flatmap list of lists of lists of tuples in Python?

3 Answers3