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MathGroup Archive 1996

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Re: Combinations function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg5470] Re: [mg5447] Combinations function?
  • From: Robert Pratt <rpratt at math.unc.edu>
  • Date: Wed, 11 Dec 1996 03:15:54 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Use the function KSubsets in the Combinatorica standard package.

In[1]:= Needs["DiscreteMath`Combinatorica`"]

In[2]:= ?KSubsets
KSubsets[l,k] returns all subsets of set l containing exactly k elements,
   ordered lexicographically.

In[2]:= KSubsets[{a,b,c,d},3]

Out[2]= {{a, b, c}, {a, b, d}, {a, c, d}, {b, c, d}}

Rob Pratt
Department of Mathematics
The University of North Carolina at Chapel Hill
CB# 3250, 331 Phillips Hall
Chapel Hill, NC  27599-3250

rpratt at math.unc.edu

On Sat, 7 Dec 1996, Erik Kulstad wrote:

> There is already a function to obtain the number of permutations possible
> from a set (or list); but does anyone know of a function to obtain the
> combinations?
> 
> For example, if the set is {a,b,c,d}, I want to list all 3-member
> combinations possible, yielding {{a,b,c},{a,b,d},{a,c,d},{b,c,d}}. 
> 
> 
> Thanks in advance,
> Erik Kulstad
> 
> 
> 
> 


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