Re: sort procedure

*To*: mathgroup at smc.vnet.net*Subject*: [mg52510] Re: [mg52483] sort procedure*From*: DrBob <drbob at bigfoot.com>*Date*: Tue, 30 Nov 2004 05:24:24 -0500 (EST)*References*: <200411290622.BAA27959@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

Here are two methods. I like the second a little better, I think. data=Array[{#,N@Sin@#}&,{5}]; Sort[data,#1[[2]]<=#2[[2]]&] data[[Ordering[data[[All,{2,1}]]]]] {{5,-0.958924},{4,-0.756802},{3,0.14112},{1,0.841471},{2,0.909297}} {{5,-0.958924},{4,-0.756802},{3,0.14112},{1,0.841471},{2,0.909297}} If the second element of each pair is exact (Sin@n rather than N@Sin@n, for instance), the Sort isn't numerical by default: data = Array[{#1, Sin[#1]} & , {5}]; Sort[data, #1[[2]] <= #2[[2]] & ] data[[Ordering[data[[All,{2, 1}]]]]] {{5, Sin[5]}, {4, Sin[4]}, {3, Sin[3]}, {1, Sin[1]}, {2, Sin[2]}} {{1, Sin[1]}, {2, Sin[2]}, {3, Sin[3]}, {4, Sin[4]}, {5, Sin[5]}} But we can do it any of these three ways: data = Array[{#1, Sin[#1]} & , {5}]; Sort[data, N[#1[[2]]] <= N[#2[[2]]] & ] Sort[data, N[#1[[2]] <= #2[[2]]] & ] data[[Ordering[N[data[[All,{2, 1}]]]]]] {{5,Sin[5]},{4,Sin[4]},{3,Sin[3]},{1,Sin[1]},{2,Sin[2]}} {{5,Sin[5]},{4,Sin[4]},{3,Sin[3]},{1,Sin[1]},{2,Sin[2]}} {{5,Sin[5]},{4,Sin[4]},{3,Sin[3]},{1,Sin[1]},{2,Sin[2]}} The last method works because, for instance, Sin[1]<=Sin[2] is unevaluated (until N is applied). That's also why the previous Sort didn't change the order. Bobby On Mon, 29 Nov 2004 01:22:30 -0500 (EST), paolo <tarpanelli at libero.it> wrote: > If I have a data serie of n paired observations (x_t,x_t-1) ordered according to time, how can i re-order this serie according to the size of x_t-1 > > The procedure Sort it seems it does not work well. > anyone has suggestions? > thanks > > P. > > > > ____________________________________________________________ > Libero ADSL: navighi gratis a 1.2 Mega, senza canone e costi di attivazione. > Abbonati subito su http://www.libero.it > > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**sort procedure***From:*"paolo " <tarpanelli@libero.it>