[R] Question regarding R plot

[David Winsemius]

On Apr 17, 2010, at 12:45 PM, Charles C. Berry wrote:

> On Sat, 17 Apr 2010, Akito Y. Kawahara wrote:
>
>> Hi, I am new to R, and have a quick question regarding an R script
>> that I received from a kind colleague.
>>
>> I am trying to determine the "peak" (maximum value) of the graph that
>> is plotted when executing the following. There is an input file  
>> called
>> "rates_values.txt" which begins as:
>>
>> rateValue
>> 0.375693
>> 0
>> 1.71274
>> 0
>> 0
>> 1.02832
>> 0
>> 0.16343
>> 1.02349
>> 0
>> 0
>> 1.47258
>> 0.703522
>> 0.390541
>> 1.83415
>>
>>
>>
>> The script, below, must run with the rates_values.txt in the same  
>> dir.
>>
>> #-------
>> rates<-read.table("rates_values.txt",header=T)
>> attach(rates)
>> scores<-function(x){
>> l<-length(rateValue)
>> total<-0
>> for(i in 1:l){
>>   value<-16*rateValue[i]*rateValue[i]*x*exp(-4*rateValue[i]*x)
>>   total<-total+value
>> }
>> return(total)
>> }
>>
>>
>> #-------
>> #preparing the plot
>> linewidth=3
>> linetype=3
>> color="blue"
>> xvalue=0.5
>>
>> plot(scores,xvalue,0,type="n",font.axis=2,xlim=c(xvalue,0))
>> curve 
>> (scores 
>> ,xvalue,add=TRUE,col=color,lty=linetype,lwd=linewidth,xlim=c(xvalue, 
>> 0))

I was a bit puzzled by these lines, since in most R plotting tasks one  
uses plot(x, y, ...). So unless the task it to plot some inverse  
function, then the arguments are reversed. Furthermore, scores was  
defined above as a function of "x", and yet is being offered to plot  
with no arguments. What is intended?


>>
>> #-------
>>
>> Can anyone help me figure out how to determine the peak (maximum
>> "scores") value in the plot that is generated?
>
>
> Yes. Anyone who knows something called 'the calculus' could help.  
> And they could point out that the 0's in the data really do not  
> matter.
>
> If the 0's are real data that should influence the result, it seems  
> there is something wrong with scores() and you might do well to get  
> a consult from a statistician.
>
> If you are still determined to solve the problem as stated, see
>
> 	?optimise
>
>
> Something like
>
> 	optimise( scores, range(rateValue), maximum=TRUE )
>
> should do it.
>
> HTH,
>
> Chuck
>
>
> It should be about 11.7
>> but I would like to get an exact value. This should be a relatively
>> easy question, but I'm new to R, and what I have tried doesn't seem  
>> to
>> work.
>>
>> Thanks!
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> Charles C. Berry                            (858) 534-2098
>                                            Dept of Family/Preventive  
> Medicine
> E mailto:cberry at tajo.ucsd.edu	            UC San Diego
> http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego  
> 92093-0901
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT