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MathGroup Archive 2000

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Re: generating subsets

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21604] Re: [mg21588] generating subsets
  • From: BobHanlon at aol.com
  • Date: Sun, 16 Jan 2000 22:43:50 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Needs["DiscreteMath`Combinatorica`"]

subSets[elements_List] := 
  Module[{k}, 
    Flatten[Table[KSubsets[elements, k], {k, 0, Length[elements]}], 1]]

subSets[{a, b, c}]

{{}, {a}, {b}, {c}, {a, b}, {a, c}, {b, c}, {a, b, c}}

Length[subSets[{a, b, c, d, e, f, g, h, i}]] // Timing

{0.25*Second, 512}

Bob Hanlon

In a message dated 1/16/2000 5:22:27 AM, mgass at bach.math.csbsju.edu writes:

>I need an _efficient_  procedure for generating all the subsets
>of a given set.  The procedure should produce output as follows:
>
>subSets[{a,b,c}]
>produces
>{{}, {a}, {b}, {c}, {a,b}, {a,c}, {b,c}, {a,b,c}}
>
>I have written a recursive procedure to do this, but
>it takes quite a while to generate, say, the 512 subsets
>of a 9 element set and I need to work with somewhat larger
>sets.
>


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