How to return every nth item in a list for Python?

Question

I have a list that is in a similar format as this:

list1 = ['random words go', 'here and','the length varies','blah',
         'i am so confused', 'lala lala la']

What code would be appropriate to return every 3rd item of the list, including the first word? This is the expected output:

["random", "here", "length", "i", "confused", "la"]

I am thinking that I should use the split function, but I don't know how to do this. Can someone also explain how I can make it so the whole list isn't in 'parts' like that? Rather, how can I turn it into one long list, if that makes sense.

possible duplicate of Pythonic way to return list of every n'th item in a larger list — dnozay
– dnozay, Commented Jul 17, 2013 at 0:14
yes, I see that now, the other question is still very relevant for one part of the problem. — dnozay
– dnozay, Commented Jul 17, 2013 at 0:43
What he really wants is to join each phrase as a string, separate by words again into a list, then pick out certain ones. Poorly worded. — erdekhayser
– erdekhayser, Commented Jul 17, 2013 at 1:24

mata · Accepted Answer · 2013-07-17 00:21:27Z

6

This is probably the most readable way to do it:

>>> list1 = ['random words go', 'here and','the length varies','blah', 'i am so confused', 'lala lala la']
>>> result = ' '.join(list1).split()[::3]
['random', 'here', 'length', 'i', 'confused', 'la']

or without joining and splitting the list again:

from itertools import chain
result = list(chain.from_iterable(s.split() for s in list1))[::3]

then you can just join the result:

>>> ' '.join(result)
'random here length i confused la'

edited Jul 17, 2013 at 0:21

answered Jul 17, 2013 at 0:11

mata

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1 Comment

John La Rooy Over a year ago

@BedSheets ' '.join(...)

Jon Clements · Accepted Answer · 2013-07-17 00:26:16Z

3

Go for:

list1 = ['random words go', 'here and','the length varies','blah', 'i am so confused', 'lala lala la']

from itertools import chain, islice    
sentence = ' '.join(islice(chain.from_iterable(el.split() for el in list1), None, None, 3))
# random here length i confused la

edited Jul 17, 2013 at 0:26

answered Jul 17, 2013 at 0:13

Jon Clements

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Hal Canary · Accepted Answer · 2013-07-17 00:24:51Z

1

[word for item in list1 for word in item.split()][0::3]

answered Jul 17, 2013 at 0:24

Hal Canary

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John La Rooy · Accepted Answer · 2013-07-17 00:22:36Z

0

Another memory efficient version

>>> list1 = ['random words go', 'here and','the length varies','blah', 'i am so confused', 'lala lala la']
>>> from itertools import chain, islice
>>> ' '.join(islice(chain.from_iterable(map(str.split, list1)), 0, None, 3))
'random here length i confused la'

answered Jul 17, 2013 at 0:22

John La Rooy

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AnnaRaven · Accepted Answer · 2013-07-17 00:27:07Z

0

To turn it into one long list:

>>> list6 = []
>>> for s in list1:
...   for word in s.split():
...     list6.append(word)
... 
>>> list6
['random', 'words', 'go', 'here', 'and', 'the', 'length', 'varies',     'blah', 'i', 'am', 'so', 'confused', 'lala', 'lala', 'la']
>>>

Then you can do the slicing as suggested with [::3]

>>> list6[::3]
['random', 'here', 'length', 'i', 'confused', 'la']

If you want it in one string:

>>> ' '.join(list6[::3])
'random here length i confused la'
>>>>

answered Jul 17, 2013 at 0:27

AnnaRaven

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tenstar · Accepted Answer · 2013-07-17 00:37:40Z

0

Try this:

>>> list1 = ['random words go', 'here and','the length varies','blah', 'i am so confused', 'lala lala la']
>>> result = ' '.join(list1).split()[::3]
['random', 'here', 'length', 'i', 'confused', 'la']

answered Jul 17, 2013 at 0:37

tenstar

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