[R] sliding window over a large vector

[Stavros Macrakis]

For this particular proble (counting), doesn't cumsum solve it
effectively and efficiently?

    vv <- cumsum(v)
    vv[n:length(vv)] - vv[1:(length(vv)-n+1]

Of course, this doesn't work for the general case of an arbitrary
sliding window function.

     -s

On 12/15/08, Chris Oldmeadow <c.oldmeadow at student.qut.edu.au> wrote:
> Hi all,
>
> I have a very large binary vector, I wish to calculate the number of
> 1's  over sliding windows.
>
> this is my very slow function
>
> slide<-function(seq,window){
>    n<-length(seq)-window
>    tot<-c()
>    tot[1]<-sum(seq[1:window])
>    for (i in 2:n) {
>       tot[i]<- tot[i-1]-seq[i-1]+seq[i]
>    }
>    return(tot)
> }
>
> this works well for for reasonably sized vectors. Does anybody know a
> way for large vectors ( length=12 million), im trying to avoid using C.
>
> Thanks,
> Chris
>
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