[Tutor] Permutations

[Kristoffer Erlandsson]

On Fri, Sep 19, 2003 at 08:50:59AM -0400, Carlo Bifulco wrote:
> Hi folks,
> 
> I have a small computing problem that I solved in an extremely ugly and 
> ad hoc way. I am submitting it here since I am sure that there must be 
> much better ways to address  it  (and I am obviously not able to find 
> them).
> 
> Here is what I would like to be able to do:
> >>> permute(["a"])
> [['a']]
> >>> permute(["a","b"])
> [['a'], ['a', 'b'], ['b']]
> >>> permute(["a","b","c"])
> [['a'], ['a', 'b'], ['a', 'c'], ['a', 'b', 'c'], ['b'], ['b', 'c'], ['c']]
> >>> permute (["a","b","c","d"])
> [['a'], ['a', 'b'], ['a', 'c'], ['a', 'd'], ['a', 'b', 'c'], ['a', 'b', 
> 'd'], ['a', 'c', 'd'], ['a', 'b', 'c', 'd'], ['b'], ['b', 'c'], ['b', 
> 'd'], ['b', 'c', 'd'], ['c'], ['c', 'd'], ['d']]

[snip]

Check this out:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/190465

especially the xuniqueCombinations function, which seems to be exactly
what you are looking for:

>>> for i in range(len(l)):
...     for a in xuniqueCombinations(l, i):
...             print a
... 
[]
['a']
['b']
['c']
['d']
['a', 'b']
['a', 'c']
['a', 'd']
['b', 'c']
['b', 'd']
['c', 'd']
['a', 'b', 'c']
['a', 'b', 'd']
['a', 'c', 'd']
['b', 'c', 'd']

Hope that helps.

Regards,

-- 
Kristoffer Erlandsson                               http://errl.info