Re: subsets of a set
- To: mathgroup at smc.vnet.net
- Subject: [mg70031] Re: subsets of a set
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Sun, 1 Oct 2006 04:08:12 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <efld41$d3i$1@smc.vnet.net>
dimmechan at yahoo.com wrote:
> 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
>
Indeed,
Sort /@ lst // Union
is enough. (I was experimenting for something else.)
Jean-Marc