all possible combinations

Duncan Smith buzzard at urubu.freeserve.co.uk
Wed Jul 13 18:07:33 CEST 2005


rbt wrote:
> On Wed, 2005-07-13 at 11:09 -0400, rbt wrote:
> 
>>On Wed, 2005-07-13 at 10:21 -0400, rbt wrote:
>>
>>>Say I have a list that has 3 letters in it:
>>>
>>>['a', 'b', 'c']
>>>
>>>I want to print all the possible 4 digit combinations of those 3
>>>letters:
>>>
>>>4^3 = 64
>>>
>>>aaaa
>>>abaa
>>>aaba
>>>aaab
>>>acaa
>>>aaca
>>>aaac
>>>...
>>>
>>>What is the most efficient way to do this? 
>>
>>Expanding this to 4^4 (256) to test the random.sample function produces
>>interesting results. It never finds more than 24 combinations out of the
>>possible 256. This leads to the question... how 'random' is sample ;)
>>
>>Try it for yourselves:
>>
>>test = list('1234')
>>
>>combinations = []
>>while 1:
>>    combo = random.sample(test, 4)
>>    possibility = ''.join(combo)
>>    if possibility not in combinations:
>>        print possibility    
>>        combinations.append(possibility)
>>        continue
>>    else:
>>        continue
>>
> 
> 
> Someone pointed out off-list that this is doing permutation, not
> combination. Is there a way to make random.sample to do combinations?
> 

Probably not in any sensible way.  But what you list in your original
post are not distinct combinations.  e.g. abaa and aaba are both 3 a's
and 1 b.  Maybe you mean that order does matter (and you're actually
looking for all distinct permutations of all combinations)?

Duncan



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