[R] A function slightly different from diff()

[dimitrijoe@ipea.gov.br]

Hi,

I wonder if the following function has already been implemented in (some) R
(package):

                summ <- function(x, lag=1) # x is a vector
                        {
                            n <- length(x)
                            x[(1+lag):n] + x[1:(n-lag)]
                        }

which (I think) the only difference from diff() is "+" instead of "-", for
differences=1.

Thank you,
Dimitri Szerman