Equivalent SAS Retain/Lag in R

A simple example: This SAS code lags a variable x and adds a variable year that has a constant value:

data one;
   retain year 2013;
   input x @@;
   y=lag1(x);
   z=lag2(x);
   datalines;
1 2 3 4 5 6
;

In R, you could write your own lag function like this:

mylag <- function(x,k) c(rep(NA,k),head(x,-k))

This single line adds k times NA at the beginning of the vector, and drops the last k values from the vector. The result is a lagged vector as given by lag1 etc. in SAS.

this allows something like :

nrs <- 1:6 # equivalent to datalines
one <- data.frame(
   x = nrs,
   y = mylag(nrs,1),
   z = mylag(nrs,2),
   year = 2013  # R automatically loops, so no extra command needed
)

The result is :

> one
  x  y  z year
1 1 NA NA 2013
2 2  1 NA 2013
3 3  2  1 2013
4 4  3  2 2013
5 5  4  3 2013
6 6  5  4 2013