[R] lead

[Adaikalavan Ramasamy]

How about

  revLag <- function(x, shift=1) rev( Lag(rev(x), shift) )

  x <- 1:5
  revLag(x, shift=2)


As a matter of fact, here is a generalized version of Lag to include 
negative shifts.

myLag <- function (x, shift = 1){

     xLen <- length(x)
     ret <- as.vector(character(xLen), mode = storage.mode(x))
     attrib <- attributes(x)
     if (!is.null(attrib$label))
         atr$label <- paste(attrib$label, "lagged", shift, "observations")

     if (shift == 0) return(x)

     if( xLen <= abs(shift) ) return(ret)

     if (shift < 0) x <- rev(x)
     retrange = 1:abs(shift)
     ret[-retrange] <- x[1:(xLen - abs(shift))]
     if (shift < 0) ret <- rev(ret)

     attributes(ret) <- attrib
     return(ret)
}

and some test examples:

myLag(1:5, shift=2)
  [1] NA NA  1  2  3

myLag(letters[1:4], shift=2)
[1] ""  ""  "a" "b"

myLag(factor(letters[1:4]), shift=2)
  [1] <NA> <NA> a    b
  Levels: a b c d

myLag(1:5, shift=-2)
  [1]  3  4  5 NA NA

myLag(letters[1:4], shift=-2)
  [1] "c" "d" ""  ""

myLag(factor(letters[1:4]), shift=-2)
  [1] c    d    <NA> <NA>
  Levels: a b c d

Regards, Adai




Aydemir, Zava (FID) wrote:
> Hi,
>  
> is there any function in R that shifts elements of a vector to the
> opposite direction of what Lag()  of the Hmisc package does? (something
> like, Lag(x, shift = -1) )
>  
> Thanks
>  
> Zava
> --------------------------------------------------------
> 
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