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Position of Last Element in List

• To: mathgroup at smc.vnet.net
• Subject: [mg94130] Position of Last Element in List
• From: Raffy <raffy at mac.com>
• Date: Fri, 5 Dec 2008 05:33:50 -0500 (EST)

I'm looking for the fastest way to find the last position of an
element at level 1 in a list.

The fastest way, which is still extremely bloated and extremely slow,
appears to be:

lastPos[v_List,p_:True,default_:$Failed]:=(
$Temp=Position[Reverse[v],p,{1},1,Heads->False];
If[Length[$Temp]>0,$Temp[[1,1]],default]
);

Any suggestions?

Use the following code to compare against lastPos:

v = Range[1000000];
Do[lastPos[v,900000],{100}]//Timing

• Follow-Ups:
  • Re: Position of Last Element in List
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
  • Re: Position of Last Element in List
    • From: Carl Woll <carlw@wolfram.com>