python create several lists from one list

Question

I have list something like mylist = [1,2,3,4,5,6] now I need to loop over this list and create 3 new lists like this

 new1 = [1,4]
 new2 = [2,5]
 new3 = [3,6]

What is the easiest way to do this?

What criterion do you have for making the new lists? Do you want to break the original into three equal parts? Separate the original every 2 items? What would happen if you had 8 items in mylist? — ASGM
– ASGM, Commented Jun 8, 2013 at 10:10
main list can have unlimited items. Need to create only 3 new lists. First and 4th item need to be in the same list. Also second and 5th, 3rd and 6th like on the example. So first list will look like ` new1=[1,4,7...] — Goran
– Goran, Commented Jun 8, 2013 at 10:22

Community · Accepted Answer · 2017-05-23 11:57:24Z

9

Use slicing:

>>> mylist = [1,2,3,4,5,6]
>>> mylist[::3]
[1, 4]
>>> mylist[1::3]
[2, 5]
>>> mylist[2::3]
[3, 6]

>>> lis = range(1,21)
>>> new1, new2, new3 = [lis[i::3] for i in xrange(3)]
>>> new1
[1, 4, 7, 10, 13, 16, 19]
>>> new2
[2, 5, 8, 11, 14, 17, 20]
>>> new3
[3, 6, 9, 12, 15, 18]

A good read in case you're new to slicing: Explain Python's slice notation

edited May 23, 2017 at 11:57

CommunityBot

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answered Jun 8, 2013 at 10:08

Ashwini Chaudhary

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2 Comments

ASGM Over a year ago

@Goran it doesn't. But if you want it to, you need to be more specific in your question about the behavior you're expecting.

Goran Over a year ago

I need 3 new lists but main list can have unlimited items. First and 4th item must be in the same list etc as on the example

jamylak · Accepted Answer · 2013-06-08 10:31:06Z

2

Maybe you should be using numpy

>>> import numpy as np
>>> arr = np.array([1,2,3,4,5,6])
>>> arr.reshape((arr.size//3, 3)).T
array([[1, 4],
       [2, 5],
       [3, 6]])

answered Jun 8, 2013 at 10:31

jamylak

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