Pulling all n-sized combinations from a list

[Swroteb]

Paul Rubin wrote:
> I think the natural approach is to make a generator that yields a
> 5-tuple for each combination, and then have your application iterate
> over that generator.  Here's my version:
>
>     def comb(x,n):
>         """Generate combinations of n items from list x"""
>         if n==0:
>             yield []
>             return
>         for i in xrange(len(x)-n+1):
>             for r in comb(x[i+1:], n-1):
>                 yield [x[i]] + r
>
>     for c in comb([1,2,3,4,5], 3):
>         print c
>
> The output is:
>     >>>
>     [1, 2, 3]
>     [1, 2, 4]
>     [1, 2, 5]
>     [1, 3, 4]
>     [1, 3, 5]
>     [1, 4, 5]
>     [2, 3, 4]
>     [2, 3, 5]
>     [2, 4, 5]
>     [3, 4, 5]
>     >>>

Ah, this definitely seems to work!  It's a lot nicer in appearance than
my previous code, that's for sure.  It actually runs in approximately
the same amount of time though.  So, using your comb method, I have the
following code now:

        myCombinations = comb(myList, 5)
        for a, b, c, d, e in myCombinations:
            # my code

myList is 48 elements in size, so I'm going to get 1712304
combinations.  From what I can tell, my speed problems aren't in the
list generation anymore.

Thanks for the assistance, Paul!  I appreciate it.  :)