Converting a list of tuples into a simple flat list

Question

Say I have a list of tuples like [(1,2), (1,3), (1,4), (1,5), (1,6)]. I’m trying to convert it to a simple list like [1,2,1,3,1,4,1,5,1,6].

How do I do this without having to iterate through each element and add the items one by one to another list?

Are there any fast and efficient ways to do this without actually iterating through the original list of tuples? Perhaps a built-in function or method?

Asked By: davidadamojr

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Source

Answer 1

lst = [(1,2), (1,3), (1,4), (1,5), (1,6)]

import itertools
list(itertools.chain(*lst))
# [1, 2, 1, 3, 1, 4, 1, 5, 1, 6]

Alternatively:

[e for l in lst for e in l]
# [1, 2, 1, 3, 1, 4, 1, 5, 1, 6]

Answered By: David Robinson

Answer 2

Use chain.from_iterable, as it avoids unnecessary all-at-once unpacking (which leads to redundant memory consumption) by lazily advancing through list:

>>> import itertools
>>> L = [(1,2), (1,3), (1,4), (1,5), (1,6)]
>>> list(itertools.chain.from_iterable(L))
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]

Answered By: ovgolovin

Answer 3

Here is the best way to do it in terms of performance and independence of special modules like itertools:

>>> l = [(1,2), (1,3), (1,4), (1,5), (1,6)] 
>>> reduce(list.__add__,map(list,l))
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]

Answered By: Pupkov-Zadnij

Answer 4

“Fundamentally, which one is faster? Using the “itertools” module, or using a list comprehension? I’m basically trying to improve my computation speed here.” – @davidadamojr

I’ve been doing some tests and I find that the code below is actually faster.

list_ = [(1, 2), (1, 3), (1, 4), (1, 5), (1, 6)]
list(sum(list_, ()))

Someone correct me if I’m wrong.

Here are some tests below.

>>> list_ = [(1, 2), (1, 3), (1, 4), (1, 5), (1, 6)]
>>> 
>>> operation_1 = lambda: [tuple_item for tuple_ in list_ for tuple_item in tuple_]
>>> def operation_2 ():
        final_list = []
        for tuple_ in list_:
            for tuple_item in tuple_:
                final_list.append(tuple_item)
        return final_list

>>> operation_3 = lambda: reduce(list.__add__, map(list, list_))
>>> def operation_4 ():
        import itertools
        return list(itertools.chain(*list_))

>>> operation_5 = lambda: list(sum(list_, ()))
>>> 
>>> operation_1()
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]
>>> operation_2()
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]
>>> operation_3()
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]
>>> operation_4()
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]
>>> operation_5()
[1, 2, 1, 3, 1, 4, 1, 5, 1, 6]
>>> 
>>> import timeit
>>> 
>>> print('operation_1 completed in %s seconds.' % (timeit.timeit(operation_1)))
operation_1 completed in 1.57890490223 seconds.
>>> print('operation_2 completed in %s seconds.' % (timeit.timeit(operation_2)))
operation_2 completed in 2.90350501659 seconds.
>>> print('operation_3 completed in %s seconds.' % (timeit.timeit(operation_3)))
operation_3 completed in 5.08437990236 seconds.
>>> print('operation_4 completed in %s seconds.' % (timeit.timeit(operation_4)))
operation_4 completed in 3.85125378138 seconds.
>>> print('operation_5 completed in %s seconds.' % (timeit.timeit(operation_5)))
operation_5 completed in 1.2623826489 seconds.

Answered By: jonathanmarvens

Converting a list of tuples into a simple flat list

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