FW: [R] basic indexing

[Prof Brian D Ripley]

On Wed, 10 Oct 2001, Warnes, Gregory R wrote:

>  >  -----Original Message-----
>  >  From: Duncan Murdoch [mailto:dmurdoch at pair.com]
>  >
>  >  On Tue, 9 Oct 2001 21:00:32 -0400, Michaell Taylor
> [michaell.taylor at reis.com]:
>  >
>  >  >in stata this would be
>  >  >gen z=x[N-1]
>  >
>  >  In R use z <- c(NA, x[-length(x)])
>
> This can be captured conveniently in the simple function:
>
> lag <- function(x, n)
> 	c( rep(NA,n), x[1:(length(x)-n)] )
>
> which is used as
>
> > y
> [1] 8 9 2 8 8
> > lag(y,1)
> [1] NA 8 9 2 8
> > lag(y,2)
> [1] NA NA 8 9 2

There is of course already a generic function called lag in R (in package
ts), so overwriting it would not be a good idea.

Especially since this one has argument n of the opposite sign to the
generic definition.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._