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MathGroup Archive 2007

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Re: Combination List

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77882] Re: Combination List
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 19 Jun 2007 06:33:03 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <f55qci$k58$1@smc.vnet.net>

Bruno Campanini wrote:
> I know combinations of 4 elements taken 3 by 3 is 4,
> that is Binomial[4,3] = 4
> How can I get the list:
> 1 2 3 
> 1 2 4
> 1 3 4
> 1 4 2
--^^^^^
I believe the last line is a typo (otherwise your request does not make 
any sense).

> The same way I get permuations list from Permutations[{...}]
> ???
> 
> Bruno
> 

What you are looking for is the list of all subsets of exactly 3 
elements. The built in function *Subsets* with its second argument set 
to {3} will do what you want.

In[1]:=
lst = {1, 2, 3, 4};
Subsets[lst, {3}]

Out[2]=
{{1, 2, 3}, {1, 2, 4}, {1, 3, 4}, {2, 3, 4}}

Regards,
Jean-Marc


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