[R] The fastest way to select and execute a few selected functions inside a function
Ales Ziberna
aleszib at gmail.com
Wed Dec 14 18:05:19 CET 2005
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
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