[SciPy-user] Finding all combinations of numbers
David Warde-Farley
dwf@cs.toronto....
Sun Jan 13 01:05:08 CST 2008
On 13-Jan-08, at 1:34 AM, Andrew Straw wrote:
> def setOfSubsets(L):
> """find all subsets of L
>
> from Alex Martelli:
> http://mail.python.org/pipermail/python-list/2001-January/067815.html
> """
> N = len(L)
> return [ [ L[i] for i in range(N)
> if X & (1L<<i) ]
> for X in range(2**N) ]
Hi Andrew,
That's a clever little snippet. :)
Just to point out to Roger in case he wants to use it: if I read it
correctly, it doesn't include L (which is, like the empty set,
unwanted in practice) because range(x) gives you [0,1,...x-1]. So for
the list [1,2,3] it will return all subsets of size 1 and size 2, plus
the empty list.
If you wanted to exclude the empty, replace range(2**N) with
range(1,2**N), skipping the number 0. If you want it to include the
entire list, make the upper limit 2**N+1.
Cheers,
DWF
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