Thanks, this is the closest to what i want (gives the same result as
cumprod()) ...but using this function seems actually slower than the loop (is
it normal ?):
a1<-runif(100000)
cadd<-function(x) Reduce("*", x, accumulate = TRUE)
looop<-function(a1){
j<-length(a1)
for(i in 2:j){
a1[i]<-a1[i-1]*a1[i]
}
a1
}
>
> system.time(cadd(a1))
user system elapsed
1.344 0.004 1.353
> system.time(cumprod(a1))
user system elapsed
0.004 0.000 0.002
> system.time(looop(a1))
user system elapsed
0.772 0.000 0.775
>
>On Tue, 13 Oct 2009, Kaveh Vakili wrote:
>
>>
>> Hi all,
>>
>> I was wondering whether it is possible to use the lapply() function
>> to alter the value of the input, something in the spirit of :
>>
>> a1<-runif(100)
>> a2<-function(i){
>> a1[i]<-a1[i-1]*a1[i];a1[i]
>> }
>> a3<-lapply(2:100,a2)
>>
>> Something akin to a for() loop, but using the lapply() infrastructure.
>> I haven't been able to get rapply() to do this.
>
>Maybe you want to check out
>
> ?Reduce
>
>For the example above, something like
>
>a3 <- Reduce( "*", a1, accumulate = TRUE )
>
>
>HTH,
>
>Chuck
>
>>
>> The reason is that the "real" a2 function is a difficult function that only
>> needs to be evaluated if the value of a1[i-1] meets some criteria.
>>
>> Thanks in advance,
>>
>> ______________________________________________
>> R-help@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:cbe...@tajo.ucsd.edu UC San Diego
>http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
>
>
>
>
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