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MathGroup Archive 2011

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list equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg121915] list equation
  • From: dimitris <dimmechan at yahoo.com>
  • Date: Thu, 6 Oct 2011 04:24:55 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

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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