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subsets of a set

  • To: mathgroup at
  • Subject: [mg70001] subsets of a set
  • From: dimmechan at
  • Date: Sat, 30 Sep 2006 05:12:23 -0400 (EDT)

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

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.


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