lowess <- function(x, y=NULL, f=2/3, iter=3, delta=.01*diff(range(xy$x[o]))) {
    xy <- xy.coords(x,y)
    n <- as.integer(length(xy$x))
    if(n == 0) stop("'x' is empty")
    o <- order(xy$x)
    .C("lowess",
       x=as.double(xy$x[o]),
       as.double(xy$y[o]),
       n,
       as.double(f),
       as.integer(iter),
       as.double(delta),
       y=double(n),
       double(n),
       double(n), PACKAGE="base")[c("x","y")]
}