identifyPCH <- function(x, y=NULL, n=length(x), labels = seq_along(x), pch=19, col=2,...)
{
    xy <- xy.coords(x, y); x <- xy$x; y <- xy$y
    sel <- rep(FALSE, length(x)); res <- integer(0)
    while(sum(sel) < n) {
        ans <- identify(x[!sel], y[!sel], n=1, plot=FALSE, ...)
        if(!length(ans)) break
        ans <- which(!sel)[ans]
        points(x[ans], y[ans], pch = pch,col=col)
        sel[ans] <- TRUE
        res <- c(res, ans)
    }
    res
}