Re: list equation

*To*: mathgroup at smc.vnet.net*Subject*: [mg121938] Re: list equation*From*: "Harvey P. Dale" <hpd1 at nyu.edu>*Date*: Fri, 7 Oct 2011 04:44:30 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201110060824.EAA22708@smc.vnet.net>

Dimitris: Union[Sort/@lst] Best, Harvey -----Original Message----- From: dimitris [mailto:dimmechan at yahoo.com] Sent: Thursday, October 06, 2011 4:25 AM To: mathgroup at smc.vnet.net Subject: [mg121938] list equation 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

**References**:**list equation***From:*dimitris <dimmechan@yahoo.com>