\HeaderA{points}{Add Points to a Plot}{points}
\methaliasA{points.default}{points}{points.default}
\keyword{aplot}{points}
\begin{Description}\relax
\code{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.
\end{Description}
\begin{Usage}
\begin{verbatim}
points(x, ...)

## Default S3 method:
points(x, y = NULL, type = "p", ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x, y}] coordinate vectors of points to plot.
\item[\code{type}] character indicating the type of plotting; actually any of
the \code{type}s as in \code{\LinkA{plot.default}{plot.default}}.
\item[\code{...}] Further graphical parameters may also be supplied as
arguments.  See Details.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The coordinates can be passed in a plotting structure
(a list with \code{x} and \code{y} components), a two-column matrix, a
time series, \dots.  See \code{\LinkA{xy.coords}{xy.coords}}.

Graphical parameters commonly used are
\describe{
\item[\code{pch}] plotting \sQuote{character}, i.e., symbol to use.  This can
either be a single character or an integer code for one of a set of
graphics symbols.  The full set of S symbols is available with
\code{pch=0:18}, see the last picture from \code{example(points)},
i.e., the examples below.

In addition, there is a special set of \R{} plotting symbols which
can be obtained with \code{pch=19:25} and \code{21:25} can be
colored and filled with different colors:
\Itemize{
\item \code{pch=19}: solid circle,
\item \code{pch=20}: bullet (smaller circle),
\item \code{pch=21}: circle,
\item \code{pch=22}: square,
\item \code{pch=23}: diamond,
\item \code{pch=24}: triangle point-up,
\item \code{pch=25}: triangle point down.
}
Values \code{pch=26:32} are currently unused, and \code{pch=32:255}
give the text symbol in a single-byte locale.  In a multi-byte locale
such as UTF-8, numeric values of \code{pch} greater than or equal to
32 specify a Unicode code point (except for the symbol font as
selected by \code{\LinkA{par}{par}(font = 5)}).

If \code{pch} is an integer or character \code{NA} or an empty
character string, the point is omitted from the plot.

Value \code{pch="."} is handled specially.  It is a rectangle of
side 0.01 inch (scaled by \code{cex}).  In addition, if \code{cex =
        1} (the default), each side is at least one pixel (1/72 inch on
the \code{\LinkA{pdf}{pdf}}, \code{\LinkA{postscript}{postscript}} and
\code{\LinkA{xfig}{xfig}} devices).

\item[\code{col}] color code or name, see \code{\LinkA{par}{par}}.
\item[\code{bg}] background (fill) color for the open plot
symbols given by \code{pch=21:25}.
\item[\code{cex}] character (or symbol) expansion: a numerical vector.
This works as a multiple of \code{\LinkA{par}{par}("cex")}.
\item[\code{lwd}] line width for drawing symbols see \code{\LinkA{par}{par}}.
}
Others less commonly used are \code{lty} and \code{lwd} for
types such as \code{"b"} and \code{"l"}.

Graphical parameters \code{pch}, \code{col}, \code{bg}, \code{cex} and
\code{lwd} can be vectors (which will be recycled as needed) giving a
value for each point plotted.  If lines are to be plotted (e.g. for
\code{type = "b"} the first element of \code{lwd} is used.

Points whose \code{x}, \code{y}, \code{pch}, \code{col} or \code{cex}
value is \code{NA} are omitted from the plot.
\end{Details}
\begin{Note}\relax
What is meant by \sQuote{a single character} is locale-dependent.

The encoding may not have symbols for some or all of the characters in
\code{pch=128:255}
\end{Note}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{plot}{plot}}, \code{\LinkA{lines}{lines}}, and the underlying
workhorse function \code{\LinkA{plot.xy}{plot.xy}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
require(stats) # for rnorm
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)

op <- par(bg = "light blue")
x <- seq(0,2*pi, len=51)
## something "between type='b' and type='o'":
plot(x, sin(x), type="o", pch=21, bg=par("bg"), col = "blue", cex=.6,
 main='plot(..., type="o", pch=21, bg=par("bg"))')
par(op)

##-------- Showing all the extra & some char graphics symbols ------------
pchShow <-
  function(extras = c("*",".", "o","O","0","+","-","|","%","#"),
           cex = 3, ## good for both .Device=="postscript" and "x11"
           col = "red3", bg = "gold", coltext = "brown", cextext = 1.2,
           main = paste("plot symbols :  points (...  pch = *, cex =", cex,")"))
  {
    nex <- length(extras)
    np  <- 26 + nex
    ipch <- 0:(np-1)
    k <- floor(sqrt(np))
    dd <- c(-1,1)/2
    rx <- dd + range(ix <- ipch %/% k)
    ry <- dd + range(iy <- 3 + (k-1)- ipch %% k)
    pch <- as.list(ipch) # list with integers & strings
    if(nex > 0) pch[26+ 1:nex] <- as.list(extras)
    plot(rx, ry, type="n", axes = FALSE, xlab = "", ylab = "", main = main)
    abline(v = ix, h = iy, col = "lightgray", lty = "dotted")
    for(i in 1:np) {
      pc <- pch[[i]]
      ## 'col' symbols with a 'bg'-colored interior (where available) :
      points(ix[i], iy[i], pch = pc, col = col, bg = bg, cex = cex)
      if(cextext > 0)
          text(ix[i] - .3, iy[i], pc, col = coltext, cex = cextext)
    }
  }

pchShow()
pchShow(c("o","O","0"), cex = 2.5)
pchShow({}, cex = 4, cextext=0, main=NULL)
\end{ExampleCode}
\end{Examples}

