#  File src/library/stats/R/lag.R
#  Part of the R package, https://www.R-project.org
#
#  Copyright (C) 1995-2012 The R Core Team
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  A copy of the GNU General Public License is available at
#  https://www.R-project.org/Licenses/

lag <- function(x, ...) UseMethod("lag")

lag.default <- function(x, k = 1, ...)
{
    if(k != round(k)) {
        k <- round(k)
        warning("'k' is not an integer")
    }
    x <- hasTsp(x)
    p <- tsp(x)
    tsp(x) <- p - (k/p[3L]) * c(1, 1, 0)
    x
}