[R] help with loop

[Gabor Grothendieck]

This is a telescoping sum that can be calculated analytically as:

(a[2] - a[1]) + ... + (a[n] - a[n-1]) = a[n] - a[1]



On Thu, Mar 12, 2009 at 9:04 AM, Rafael Moral
<rafa_moral2004 at yahoo.com.br> wrote:
> Dear useRs,
> I'm trying to write a loop to sum my data in the following way:
> (the second - the first) + (the third - the second) + (the fourth - the third) + ...
> for each column.
>
> So, I wrote something like this:
>
>   c <- list()
>   for(i in 1:ncol(mydata)) {
>   for(j in 2:nrow(mydata)) {
>   c[[i]] <- sum(yc[j,i] - yc[(j-1),i])
>   }}}
>
> As for the columns it works pretty fine, but it only returns the last subtraction, however, I need the sum of all subtractions.
>
> Any ideas?
>
> Regards,
> Rafael.
>
>
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