Find last NZ in list

*To*: mathgroup at smc.vnet.net*Subject*: [mg46102] Find last NZ in list*From*: carlos at colorado.edu (Carlos Felippa)*Date*: Fri, 6 Feb 2004 04:15:25 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

This is kind of an "esthetics" question. In a program I am writing I need to find the last nonzero entry of a 1D list millions of times. For example FindLastNonzero[{1,2,3,4,0,a,b-b,0,0}] -> 6, and FindLastNonzero[{0,0,0,0,0,0,0}] -> 0. Here are two ugly C-style implementations: FindLastNonzero[a_]:=Module[{n=Length[a]}, For [i=n,i>0,i--, If [a[[i]]==0,Continue[],Return[i],Return[i]]]; Return[0]]; FindLastNonzero[a_]:=Module[{n=Length[a]}, For [i=n,i>0,i--, If [a[[i]]!=0,Return[i],Continue[i],Return[i]]]; Return[0]]; Is there a built-in function, or something more elegant, available to do this job? Find only works for text streams. Note that the If case "cannot tell if entry is NZ" is important for symbolic lists. That case should be evaluated as NZ.

**Follow-Ups**:**Re: Find last NZ in list***From:*János Löbb <janos.lobb@yale.edu>

**Re: Find last NZ in list***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>