Re: Re: Find last NZ in list
- To: mathgroup at smc.vnet.net
- Subject: [mg46187] Re: [mg46163] Re: Find last NZ in list
- From: János Löbb <janos.lobb at yale.edu>
- Date: Tue, 10 Feb 2004 00:06:00 -0500 (EST)
- References: <200402060915.EAA19244@smc.vnet.net> <c02cp5$54m$1@smc.vnet.net> <200402091054.FAA20993@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
I see... I was a little naive...
Here is a better one - still not using explicit loop.
nn = 20000
a = Table[0, {nn}];
a[[666]] = dante
a[[665]] = lucifer
a[[111]] = Maria
Timing[Last[Position[a, x_ /; (x 0 || Head[x] == Symbol)]]]
{0.54 Second, {666}}
Mea culpa for the previous one.
J?nos
On Feb 9, 2004, at 5:54 AM, Carlos Felippa wrote:
> Many thanks for the submissions. Here is a comparison of five
> functions and their timings on a mac g4.
>
> FindLastNonzero[a_]:=Module[{n=Length[a]},
> For [i=n,i>0,i--, If [a[[i]]==0,Continue[],Return[i],
> Return[i]]]; Return[0]]; (* CAF *)
> FindLastNonzero1[a_]:=Module[{n=Length[a]},
> For [i=n,i>0,i--, If [a[[i]]!=0,Return[i],Continue[],
> Return[i]]]; Return[0]]; (* CAF *)
> FindLastNonzero2[a_]:=Catch[Do[If[a[[i]]=!
> =0,Throw[i]],{i,Length[a],1,-1}];0];
> (* Andrzej Kozlowski *)
> FindLastNonzero3[a_]:=First[Position[a, _?(# == 0 &)]] - 1; (*
> J?nos Lobb *)
> FindLastNonzero4[lst_]:=
> Module[{tmp=DeleteCases[lst,0]},
> If[Length[tmp]!=0,Last[tmp],0] ]; (* Bo Le *)
> FindLastNonZero5[liste_] :=
> If[Position[(StringMatchQ[#1, "0"] & ) /@
> ToString /@ liste, False] != {},
> Last[Position[(StringMatchQ[#1, "0"] & ) /@
> ToString /@ liste, False]][[1]], 0]; (* Florian Jaccard *)
>
> nn=20000; a=Table[0,{nn}]; a[[666]]=dante;
> Print[Timing[FindLastNonzero [a]]];
> Print[Timing[FindLastNonzero1[a]]];
> Print[Timing[FindLastNonzero2[a]]];
> Print[Timing[FindLastNonzero3[a]]]; (* fails on this example *)
> Print[Timing[FindLastNonzero4[a]]]; (* returns entry, not index *)
> (* Print[Timing[FindLastNonzero5[a]]]; does not work *)
>
> {0.55 Second,666}
> {0.4 Second,666}
> {0.133333 Second,666}
> {0.2 Second,{0}}
> {0.0333333 Second,dante}
>
> FindLastNonzero4 is fastest but requires another Position search for
> the entry index . Of those that work in one shot, FindLastNonzero2 is
> fastest.
>
> The most elegant functional solution would be to say
> i = FirstPosition[Reverse[a],!=0];
> as a built in function. But this doesnt exist.
>
>
-------------------------------------------------
clear perl code is better than unclear awk code; but NOTHING comes
close to unclear perl code
http://www.faqs.org/faqs/computer-lang/awk/faq/
- References:
- Find last NZ in list
- From: carlos@colorado.edu (Carlos Felippa)
- Re: Find last NZ in list
- From: carlos@colorado.edu (Carlos Felippa)
- Find last NZ in list