On Sat, Sep 24, 2011 at 12:06 AM, Dr. Phillip M. Feldman
<phillip.m.feld...@gmail.com> wrote:
>
> I wrote a small generator function that produces multinomial combinations.
> (Python's itertools module does ordinary combinations, but not multinomial
> combinations). The code essentially works, except that the the last
> combination in each tuple is not enclosed in a nested tuple:
>
> In [2]: x= multinomial_combinations(range(7),[2,1,2])
>
> In [3]: x.next()
> Out[3]: ((0, 1), (2,), 3, 4)
>
> (The 3 and 4 should be enclosed in a nested tuple).
>
> Any suggestions as to what I'm doing wrong will be appreciated. My code
> follows:
>
> def multinomial_combinations(items, ns):
>
> if len(ns) == 1:
> for c in itertools.combinations(items, ns[0]):
> yield c
FWIW, changing the base case to:
if not ns:
yield ()
appears to fix the issue. (Disclaimer: Have not done additional testing.)
Cheers,
Chris
> else:
> for c_first in itertools.combinations(items, ns[0]):
> items_remaining= set(items) - set(c_first)
> for c_other in multinomial_combinations(items_remaining, ns[1:]):
> yield (c_first,) + c_other
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