Reorder an array in python

Question

I want to sort an array, so it starts off at

order = [0,1,2,3,4,5] #loop around trying all columns`

and then will go through, trying all combinations of this so 1,2,3,4,5,0 etc, and stop once it has tried all of them.

Is there anyway to do this in python?

• Grijesh Chauhan: order.sort() works..
• santosh-patil: Do you want all the rotations or all the permutations?
• Niccolò: Do you want to produce all possible permutations or you want to find A particular one and stop the search there?

Answer 1

If you just want to "rotate" a list, have a look at the deque class:

>>> from collections import deque
>>> order = [0,1,2,3,4,5]
>>> order.sort() # ensure order is sorted
>>> q = deque(order)
>>> for _ in xrange(len(q)):
... q.rotate(-1)
... print q
...
deque([1, 2, 3, 4, 5, 0])
deque([2, 3, 4, 5, 0, 1])
deque([3, 4, 5, 0, 1, 2])
deque([4, 5, 0, 1, 2, 3])
deque([5, 0, 1, 2, 3, 4])
deque([0, 1, 2, 3, 4, 5])
>>>

Answer 2

If you mean all permutations, rather than the rotations in Dominic's answer:

import itertools
permutations = [ p for p in itertools.permutations(order) ]

There's 720 permutations in total so I won't print them :)

• André Laszlo: [p for p in <iterable>] <==> list(<iterable>) Converting an iterator to a list can be very expensive, especially for permutations, which would consume O(n!) memory. Yikes.
• James Little: Sure, depending on what he wants to do with the permutations, he may not need them stored in a list. In which case much better to iterate over itertools.permutations(order) directly. Good point!