[R] Loop removal possible?

[Martyn Plummer]

I think this will work:

hilf.w <- function(w){
        y <- 0:sum(w)
        z <- y*(y+1)/2
        indices <- cumsum(c(1,w))
        diff(z[indices])
}

Martyn

On 21-Aug-00 Jan Goebel wrote:
> Dear all,
> 
> may be somebody have ideas to my following problem:
> 
> I have to multiplicate each element of a vector with his position
> in the sorted vector. This isn't a problem ;-)
> But now i have a weighting vector with the weight of each observation,
> and my problem starts. A little example (due to my bad english) maybe
> helps to understand:
> 
> x<-c(10,40,50,100)  # income vector for instance
> w<-c(2,1,3,2)       # the weight for each observation in x with the same
> length
> 
> simple is without the weighting
> x * (1:length(x))
> 
> with weighting the expanded x vector looks like
> "position"    x[i]
> 1             10
> 2             10
> 3             40
> 4             50
> 5             50
> 6             50
> 7             100
> 8             100
> 
> To avoid expanding (memory and time consuming) i want to calculate
> 
> (1+2)*10
> 3 *40
> (4+5+6)*50
> (7+8)*100
> 
> My solution looks like:
> 
> hilf.w <- function(w) {
>   k <- rep(0,length(w))
>   e <- cumsum(w)       # the end position
>   a <- e-(w-1)         # the beginning position
>   for (i in 1:length(w)) {# <<- this loop i want to remove ??
>     k[i] <- sum(a[i]:e[i])
>   }
>   return(k)
> }
> 
> for the example the function calculate:
> 
>> hilf.w(w)
> [1]  3  3 15 15
> 
> Thanks a lot in advance for any suggestions,
> 
> Jan Goebel (jgoebel at diw.de)
> DIW Berlin
> SOEP
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