Finding every nth element in a list

Question

How can I find every nth element of a list?

For a list [1,2,3,4,5,6], returnNth(l,2) should return [1,3,5] and for a list ["dog", "cat", 3, "hamster", True], returnNth(u,2) should return ['dog', 3, True]. How can I do this?

its was introduced in python2.3; see the docs for that--> http://docs.python.org/release/2.3.5/whatsnew/section-slices.html — namit, Feb 04 '13 at 04:19

score 47 · Accepted Answer · edited Nov 16 '19 at 15:07

47

You just need lst[::n].

Example:

>>> lst=[1,2,3,4,5,6,7,8,9,10]
>>> lst[::3]
[1, 4, 7, 10]
>>>

edited Nov 16 '19 at 15:07

Mark Amery

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answered Feb 04 '13 at 04:15

us2012

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what if we want [2,5,8] ? – Rohan Marwah Dec 02 '20 at 12:59
4

@Cosmic `lst[1::3]` – us2012 Dec 02 '20 at 13:01

score 3 · Answer 2 · edited Nov 16 '19 at 15:04

3

In [119]: def returnNth(lst, n):
   .....:     return lst[::n]
   .....:

In [120]: returnNth([1,2,3,4,5], 2)
Out[120]: [1, 3, 5]

In [121]: returnNth(["dog", "cat", 3, "hamster", True], 2)
Out[121]: ['dog', 3, True]

edited Nov 16 '19 at 15:04

Mark Amery

143,130
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answered Feb 04 '13 at 04:16

avasal

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sufinsha · Answer 3 · 2013-02-04T04:42:03.850

-1

I you need the every nth element....

  def returnNth(lst, n):
        # 'list ==> list, return every nth element in lst for n > 0'
        return lst[::n]

edited Feb 04 '13 at 04:42

answered Feb 04 '13 at 04:27

sufinsha

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-1; this doesn't add anything new that wasn't already provided by the other two answers, posted 10 minutes' earlier. – Mark Amery Nov 16 '19 at 15:09

Finding every nth element in a list

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