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MathGroup Archive 2006

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RE: subsets of a set

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70051] RE: [mg70001] subsets of a set
  • From: "Erickson Paul-CPTP18" <Paul.Erickson at Motorola.com>
  • Date: Sun, 1 Oct 2006 04:09:40 -0400 (EDT)

Do you want 
lst = Subsets[Range[7], {3}]
? 

-----Original Message-----
From: dimmechan at yahoo.com [mailto:dimmechan at yahoo.com] 
To: mathgroup at smc.vnet.net
Subject: [mg70051] [mg70001] subsets of a set

In page 226 of John Gray's Mastering Mathematica (unfortunately I had the 1994's edition) there is the following exercise:

"Given a finite set (presented as a list) and an integer k find all k-element subsets of the set".

There is one solution however for practicing (no there is no professor that asked me this for homeworks! I work individually...) I search for other

So considering the following list

lst = Tuples[Range[7], 3];

I can erase the sublists containg at least two same elements

Cases[lst, {x_, y_, z_} /; x ß?  y && x ß?  z && y ß?  z]

but after I cannot erase the permutations of e.g. {1,2,3}; that is in the output there are the sublists {1,2,3}, {2,1,3},{3,1,2} e.t.c. for other triplets.

I look for both functional as well pattern matching approaches.

Thanks


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