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Re: list equation

  • To: mathgroup at
  • Subject: [mg121938] Re: list equation
  • From: "Harvey P. Dale" <hpd1 at>
  • Date: Fri, 7 Oct 2011 04:44:30 -0400 (EDT)
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-----Original Message-----
From: dimitris [mailto:dimmechan at]
Sent: Thursday, October 06, 2011 4:25 AM
To: mathgroup at
Subject: [mg121938] list equation

Hello to all.


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


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