[R] The fastest way to select and execute a few selected functions inside a function

[Ales Ziberna]

----- Original Message ----- 
From: "Ales Ziberna" <aleszib at gmail.com>
To: "R-help" <r-help at stat.math.ethz.ch>
Sent: Wednesday, December 14, 2005 6:05 PM
Subject: The fastest way to select and execute a few selected functions 
inside a function


Dear useRs?



I have the following problem! I have a function that calls one or more
functions, depending on the input parameters. I am searching for the fastest
way to select and execute the selected functions and return their results in
a list. The number of possible functions is 10, however usually only 2 are
selected (although sometimes more, even all).



For examples, if I have function "myf" and the possible functions that I
want to call are "mean", "max" and "sum". I have thought of one way (myf) to
do that and am interested if there maybe exists a faster way (the speed is
very important, since this can be repeated millions of times in my
function).





myf<-function(FUN, x){

            f<-list(mean=mean, max=max, sum=sum)

            res<- vector( mode="list")

            for(i in FUN){

                        res[[i]]<-f[[i]](x)

            }

            return(res)

}

myf(FUN=c("mean","max"),x=1:10)





In this case, it would be faster if I would compute all functions, even if I
need only one:

myf.all<-function(x){

            list(mean=mean(x), max=max(x), sum=sum(x))

}



> gc();system.time(for(i in 1:10000)myf.all(1:20))

         used (Mb) gc trigger (Mb) max used (Mb)

Ncells 165659  4.5     350000  9.4   350000  9.4

Vcells  61135  0.5     786432  6.0   283043  2.2

[1] 0.90 0.00 1.08   NA   NA

> gc();system.time(for(i in 1:10000)myf(FUN="mean",1:20))

         used (Mb) gc trigger (Mb) max used (Mb)

Ncells 165659  4.5     350000  9.4   350000  9.4

Vcells  61135  0.5     786432  6.0   283043  2.2

[1] 1.14 0.00 1.40   NA   NA



This does (usually) not happen in my case, since most of functions I
consider are more complex.



Thanks in advance for any suggestions!


Best regards,

Ales Ziberna