

   AAdddd PPooiinnttss ttoo aa PPlloott

        points(x, ...)
        points.default(x, y=NULL, type="p", pch=1, col="black", bg=NA, cex=1, ...)

   AArrgguummeennttss::

       x, y: coordinate vectors of points to plot.

       type: character indicating the type of plotting; actu-
             ally any of the `type's as in `plot(..)'.

        pch: plotting `character', i.e. symbol to use.  `pch'
             can either be a `character' or an integer code for
             a set of graphics symbols.  The full set of S sym-
             bols is available with `pch=0:18'.

             In addition, there is a special set of R plotting
             symbols which can be obtained with `pch=19:25' and
             can be colored and filled with different colors:

                * `pch=19': solid circle,

                * `pch=20': bullet,

                * `pch=21': circle,

                * `pch=22': square,

                * `pch=23': diamond,

                * `pch=24': triangle point-up,

                * `pch=25': triangle point down.

        col: color code or name, see `colors', `palette'.

         bg: background (``fill'') color for open plot symbols

        cex: character expansion

        ...: Further graphical parameters (see `plot.xy' and
             `par') may also be supplied as arguments.

   DDeessccrriippttiioonn::

        `points' is a generic function to draw a sequence of
        points at the specified coordinates.  The specified
        character(s) are plotted, centered at the coordinates.

        Graphical parameters are permitted as arguments to this
        function.

   SSeeee AAllssoo::

        `plot', `lines', and the underlying ``primitive''
        `plot.xy'.

   EExxaammpplleess::

        plot(-4:4, -4:4, type = "n")# setting up coord. system
        points(rnorm(200), rnorm(200), col = "red")
        points(rnorm(100)/2, rnorm(100)/2, col = "blue", cex = 1.5)

        ##-------- Showing all the extra & some char graphics symbols ------------
        Pex <- if(.Device=="postscript") 5 else 20
        ipch <- 1:(np <- 25+11); k <- floor(sqrt(np)); dd <- c(-1,1)/2
        rx <- dd + range(ix <- (ipch-1) %/% k)
        ry <- dd + range(iy <- 3 + (k-1)-(ipch-1) %% k)
        pch <- as.list(ipch)
        pch[25+ 1:11] <- as.list(c("*",".", "o","O","0","+","-",":","|","%","#"))
        plot(rx, ry, type="n", axes = F, xlab = "", ylab = "",
             main = "plot symbols :  points (..  pch = * )")
        abline(v = ix, h = iy, col = "lightgray", lty = "dotted")
        for(i in 1:np) {
          pc <- pch[[i]]
          points(ix[i], iy[i], pch = pc, col = "red", bg = "yellow", cex = Pex)
          ## red symbols with a yellow interior (where available)
          text(ix[i] - .3, iy[i], pc, col = "brown", cex = 1.5)
        }

