Re: list equation
- To: mathgroup at smc.vnet.net
- Subject: [mg121933] Re: list equation
- From: Peter Pein <petsie at dordos.net>
- Date: Fri, 7 Oct 2011 04:43:36 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <j6jpek$me8$1@smc.vnet.net>
Am 06.10.2011 10:38, schrieb dimitris:
> Hello to all.
>
> Let
>
> lst = Tuples[Range[100], 2];
>
> In the previous list appear elements such us {x,y} and {y,x}. (e.g.
> {3,4} and {4,3}).
> I want to create a new list with {y,x} dropped (that is, in the new
> list appears only {3,4}
> and not {4,3}).
>
> I use
>
> lstnew = Union[lst, SameTest -> (#1 == Reverse[#2] &)]
>
> However it is needed almost 150 sec for this procedure ($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
>
lstnew = Subsets[Range[100], {2}];
or if you need lst for other purposes:
lstnew = Union[Sort /@ lst];
hth,
Peter