Possible Duplicate:
Making a flat list out of list of lists in Python
In python 3, how can I convert a list [['a'], ['b']] to ['a','b'] ?
I am a beginner programmer and have not been able to solve this problem myself.
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Sasha Ivanov
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Apart from it being a duplicate, what have you tried? – phant0m Nov 24 '12 at 22:35
3 Answers
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Try this:
a = [['a'],['b']]
a = [item for list in a for item in list]
print a
>>>['a', 'b']
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Try:
[i[0] for i in [['a'], ['b']]
>>> ['a','b']
alexvassel
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3@AshwiniChaudhary working of this line depends on a question that was asked. – alexvassel Nov 24 '12 at 22:39
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Use itertools, specifically itertools.chain (this is much better than devising your own way of doing it):
>>> l = [['a'], ['b']]
>>> print(list(itertools.chain.from_iterable(l)))
['a', 'b']
This is faster than the pure list-comprehension solution as well:
$ python -mtimeit -s'l=[[1,2,3],[4,5,6], [7], [8,9]]*99' '[item for sublist in l for item in sublist]'
10000 loops, best of 3: 53.9 usec per loop
$ python -mtimeit -s'l=[[1,2,3],[4,5,6], [7], [8,9]]*99' 'list(itertools.chain.from_iterable(l))'
10000 loops, best of 3: 29.5 usec per loop
(Tests adapted from this question)
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@RohitJain That is also possible, but probably not as efficient as `itertools`. – arshajii Nov 24 '12 at 22:43
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1@RohitJain `itertools.chain()` should be preferred over `sum()`,coz for e.g `sum()` will not work for list of tuples.even documentation says that http://docs.python.org/2/library/functions.html#sum, we should prefer `chain()`. – Ashwini Chaudhary Nov 24 '12 at 22:49
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