>>>>> "MikeM" == Michael M Meyer <mikem at
salter-point.com>
>>>>> on Sat, 07 Sep 2002 18:40:01 -0700 writes:
MikeM> which(x==max(x)) will return the indices fo all
MikeM> elements that are equal to the max. So the first max
MikeM> would be which(x==max(x))[1] (At least this works in
MikeM> R, I assume it does in S-plus....?) --Mike
yes, (of course).
However, the above solution is quite sub-optimal at least in
principle:
1) run through all of x finding the *value* of the max()
2) run through all of x comparing x[i] with the max(), returning
a logical vector of TRUE/FALSE
3) extract the TRUE indices
For this reason, and because it's such a common task, I had
introduced the functions
which.min() and which.max()
into R, a while ago [R 1.1.0 (June 15, 2000)].
Speed comparison when x is of length 10000,
shows a speedup of about a factor of 13 {varying between 9 & 20}.
S-plus is not yet compatible here.. :-) ;-)
>> ***> Abdulkadir Hussein wrote (Fri, 06 Sep 2002 17:55:33
>> MDT) Hi S-group, Is anyone aware of a function in S-plus
>> which returns the index (position) of the first global
>> max of a vector x? ... I would appreciate any
>> suggestions..
>>
>> Regards Abdul
>> __________________________________________________________________
>> Abdulkadir Ahmed Hussein Department of Mathematical
>> Sciences University of Alberta Edmonton, Alberta Canada
>> T6G 2G1 Office: CAB 664 Phone: (403)436-4943 W3:
>> http://www.stat.ualberta.ca/~hussein
>> ___________________________________________________________________
Martin Maechler <maechler at stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum LEO C16 Leonhardstr. 27
ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND
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