Re: How to find the index of a maximal element in a list?

*To*: mathgroup at smc.vnet.net*Subject*: [mg72944] Re: How to find the index of a maximal element in a list?*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Fri, 26 Jan 2007 06:22:27 -0500 (EST)*Organization*: The Open University, Milton Keynes, UK*References*: <epa2rr$iue$1@smc.vnet.net>

Valter Sorana wrote: > I may have a mental block, but I cannot find anything better than > > Position[listName,Max[listName]] > > that traverses the list twice - once to find the maximum and once to find where it is. > > Isn't there a way to get both the index and the max value in one go? > > (of course one could write a loop that does this, but I want to avoid loops) > > Thanks, > > Valter. > Hi Valter, You could use the function Ordering [1] with its last argument set to -1. (Ordering[list, -n] gives the positions of the last n elements of Sort[list]; consequently, Ordering[list, -1] gives the position of the largest element in list.) In[1]:= lst=Table[Random[], {10^7}]; In[2]:= Position[lst,Max[lst]]//Timing Out[2]= {13.266 Second,{{8204211}}} In[3]:= Ordering[lst,-1]//Timing Out[3]= {0.125 Second,{8204211}} Regards, Jean-Marc [1] http://documents.wolfram.com/mathematica/functions/Ordering