Re: list equation

*To*: mathgroup at smc.vnet.net*Subject*: [mg121929] Re: list equation*From*: Richard Hofler <rhofler at bus.ucf.edu>*Date*: Fri, 7 Oct 2011 04:42:53 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201110060824.EAA22708@smc.vnet.net>

Hello Dimitris, Try this. In[36]:= Clear[lst] lst=Tuples[Range[5],2] Length[lst] shortLst = DeleteDuplicates[lst,#1==Reverse[#2]&] Length[shortLst] Out[37]= {{1,1},{1,2},{1,3},{1,4},{1,5},{2,1},{2,2},{2,3},{2,4},{2,5},{3,1},{3,2},{3,3},{3,4},{3,5},{4,1},{4,2},{4,3},{4,4},{4,5},{5,1},{5,2},{5,3},{5,4},{5,5}} Out[38]= 25 Out[39]= {{1,1},{1,2},{1,3},{1,4},{1,5},{2,2},{2,3},{2,4},{2,5},{3,3},{3,4},{3,5},{4,4},{4,5},{5,5}} Out[40]= 15 Richard Hofler ________________________________________ From: dimitris [dimmechan at yahoo.com] Sent: Thursday, October 06, 2011 4:24 AM To: mathgroup at smc.vnet.net Subject: [mg121929] 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>