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Re: list equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg121974] Re: list equation
  • From: Chris Arthur <chris.arthur1 at gmail.com>
  • Date: Fri, 7 Oct 2011 04:51:02 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201110060824.EAA22708@smc.vnet.net>

Table[{i,j},{i,1,i},{j,1,100}]

On Thu, Oct 6, 2011 at 3:24 AM, dimitris <dimmechan at yahoo.com> wrote:

> Hello to all.
>
> Let
>
> lst = Tuples[Range[100], 2];
>
> In the previous list appear elements such us {x,y} and {y,x}. (e.g.
> {3,4} and {4,3}).
> I want to create a new list with {y,x} dropped (that is, in the new
> list appears only {3,4}
> and not {4,3}).
>
> I use
>
> lstnew = Union[lst, SameTest -> (#1 == Reverse[#2] &)]
>
> However it is needed almost 150 sec for this procedure ($Version->5.2
> for Windows)
> I know that my laptop is too old but I guess there is a more efficient
> way to
> create lstnew.
>
> Any ideas?
>
> Thanks a lot
>
> Dimitris
>


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