Re: List manipulation

*To*: mathgroup at smc.vnet.net*Subject*: [mg7433] Re: [mg7390] List manipulation*From*: Robert Pratt <rpratt at math.unc.edu>*Date*: Sat, 31 May 1997 15:08:31 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

You mean that there will be 8-choose-4 = 70 elements. Try 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[Range[8],4] Out[2]= {{1, 2, 3, 4}, {1, 2, 3, 5}, {1, 2, 3, 6}, {1, 2, 3, 7}, > {1, 2, 3, 8}, {1, 2, 4, 5}, {1, 2, 4, 6}, {1, 2, 4, 7}, {1, 2, 4, 8}, > {1, 2, 5, 6}, {1, 2, 5, 7}, {1, 2, 5, 8}, {1, 2, 6, 7}, {1, 2, 6, 8}, > {1, 2, 7, 8}, {1, 3, 4, 5}, {1, 3, 4, 6}, {1, 3, 4, 7}, {1, 3, 4, 8}, > {1, 3, 5, 6}, {1, 3, 5, 7}, {1, 3, 5, 8}, {1, 3, 6, 7}, {1, 3, 6, 8}, > {1, 3, 7, 8}, {1, 4, 5, 6}, {1, 4, 5, 7}, {1, 4, 5, 8}, {1, 4, 6, 7}, > {1, 4, 6, 8}, {1, 4, 7, 8}, {1, 5, 6, 7}, {1, 5, 6, 8}, {1, 5, 7, 8}, > {1, 6, 7, 8}, {2, 3, 4, 5}, {2, 3, 4, 6}, {2, 3, 4, 7}, {2, 3, 4, 8}, > {2, 3, 5, 6}, {2, 3, 5, 7}, {2, 3, 5, 8}, {2, 3, 6, 7}, {2, 3, 6, 8}, > {2, 3, 7, 8}, {2, 4, 5, 6}, {2, 4, 5, 7}, {2, 4, 5, 8}, {2, 4, 6, 7}, > {2, 4, 6, 8}, {2, 4, 7, 8}, {2, 5, 6, 7}, {2, 5, 6, 8}, {2, 5, 7, 8}, > {2, 6, 7, 8}, {3, 4, 5, 6}, {3, 4, 5, 7}, {3, 4, 5, 8}, {3, 4, 6, 7}, > {3, 4, 6, 8}, {3, 4, 7, 8}, {3, 5, 6, 7}, {3, 5, 6, 8}, {3, 5, 7, 8}, > {3, 6, 7, 8}, {4, 5, 6, 7}, {4, 5, 6, 8}, {4, 5, 7, 8}, {4, 6, 7, 8}, > {5, 6, 7, 8}} In[3]:= Length[%] Out[3]= 70 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 http://www.math.unc.edu/Grads/rpratt/ On Fri, 30 May 1997, V. Nandagopal wrote: > Hello, > > I have a list X={1,2,3,4,5,6,7,8}. How do I get a list of the > folllowing kind: > > S={{1,2,3,4}, {1,2,3,5}, {1,2,3,6}, .....}. > > S will have 8-choose-2 = 70 elements. Each element of S should have length > 4. > > Is there any function which does such list making? Something of > the form > > ?????[list, n] > > Thanks in advance. > > > V. Nandagopal > School of Mathematics > Tata Institute of Fundamental Research > Colaba, Bombay 400 005, India > > e-mail: nandgopa at math.tifr.res.in > > > >