I have a python list and an index of an item I want to start a loop on the list starting from the element after my index. For example I have:
original_list = [1,2,3,4,5]
my_index = 2
new_list = [4,5,1,2,3]
I am trying to achieve the new list.
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3 Answers
7
Just use list slicing, like this
>>> original_list, my_index = [1, 2, 3, 4, 5], 2
>>> original_list[my_index + 1:] + original_list[:my_index + 1]
[4, 5, 1, 2, 3]
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thefourtheye
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For large lists, use itertools.islice – fredtantini Jan 06 '15 at 09:24
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@fredtantini and `itertools.chain` but this would only help for very huge lists – jamylak Jan 06 '15 at 09:55
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An alternative is `list(islice(cycle(original_list), my_index+1, my_index+len(original_list)+1)` but i can't think of a case where this would be useful haha – jamylak Jan 06 '15 at 09:58
4
Or you can use collections.deque and can use deque.rotate.
In [70]: original_list = [1,2,3,4,5]
In [71]: import collections
In [72]: deq = collections.deque(original_list)
In [77]: deq.rotate(2)
In [78]: deq
Out[78]: deque([4, 5, 1, 2, 3])
Vishnu Upadhyay
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This is another possibility:
>>> olist = [1,2,3,4,5]
>>> print [olist[n-2] for n in xrange(len(olist))]
[4, 5, 1, 2, 3]
Eithos
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