The R Project SVN R

## file update.R
## copyright (C) 1998 W. N. Venables and B. D. Ripley
##
update.default <-
    function (object, formula., ..., evaluate = TRUE)
{
    if (is.null(call <- object$call))
    stop("need an object with call component")
    extras <- match.call(expand.dots = FALSE)$...
    if (!missing(formula.))
    call$formula <- update.formula(formula(object), formula.)
    if(length(extras) > 0) {
    existing <- !is.na(match(names(extras), names(call)))
    ## do these individually to allow NULL to remove entries.
    for (a in names(extras)[existing]) call[[a]] <- extras[[a]]
    if(any(!existing)) {
        call <- c(as.list(call), extras[!existing])
        call <- as.call(call)
    }
    }
    if(evaluate) eval(call, sys.frame(sys.parent()))
    else call
}

update.formula <- function (old, new) {
    tmp <- .Internal(update.formula(as.formula(old), as.formula(new)))
    formula(terms.formula(tmp))
}