[R] scoping issues?

[Jan T. Kim]

On Thu, Dec 08, 2005 at 06:47:05AM -0500, tom wright wrote:
> Can anyone please help me understand whats happening here?
> Thanks
> Tom
> 
> getAmpRatio<-function(v_amps){
>     #calculates the amplitude ratios between the 3 largest amps and the
> rest
>     bigamp<-0
>     map<-rep(TRUE,length(v_amps))
> 
>     for(iLoc in 1:3){
>         bigamp<-bigamp+max(v_amps)
>         map[which.max(v_amps)]<-FALSE
>         v_amps<-v_amps[map]
>         map<-rep(TRUE,length(v_amps))
>     }
>     browser()
>     return(bigamp/mean(v_amps))
> }
> 
> amps<-c(1,2,3,3,3,2,1)
> getAmpRatio(amps)
> 
> Browse[1]> v_amps
> [1] 1 1 2 2 1
> Browse[1]> c(amps[1],amps[2],amps[3],amps[7],amps[8])
> [1] 1 1 2 2 1
> Browse[1]> mean(v_amps)
> [1] 1.4

This computes the mean of the set {1, 1, 2, 2, 1}, which is 7 / 5 = 1.4

> Browse[1]> mean(amps[1],amps[2],amps[3],amps[7],amps[8])
> [1] 1

This computes the mean of amps[1], i.e. of the set {1}, which is 1 / 1 = 1.

The remaining parameters are matched to the special variable length
formal parameter of the mean function, which, upon eventual dispatch
to mean.default are basically ignored, as far as I see.

Perhaps, you meant

    mean(c(amps[1], amps[2], amps[3], amps[7], amps[8]))

which effectively calls mean with one argument of length 5, as opposed
to 5 arguments of length 1, as your call does.

Best regards, Jan
-- 
 +- Jan T. Kim -------------------------------------------------------+
 |             email: jtk at cmp.uea.ac.uk                               |
 |             WWW:   http://www.cmp.uea.ac.uk/people/jtk             |
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