\name{points}
\alias{points}
\alias{points.default}
\title{Add Points to a Plot}
\description{
  \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.
}
\usage{
points(x, \dots)

\method{points}{default}(x, y = NULL, type = "p", pch = par("pch"),
       col = par("col"), bg = NA, cex = 1, \dots)
}
\arguments{
  \item{x, y}{coordinate vectors of points to plot.}
  \item{type}{character indicating the type of plotting; actually any of
    the \code{type}s as in \code{\link{plot}}.}
  \item{pch}{plotting \dQuote{character}, i.e., symbol to use.  \code{pch} can
    either be a \code{\link{character}} or an integer code for 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.
    % (currently, \R uses circles instead of octagons).

    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 the encoding in use (see \code{\link{postscript}}).
  }
  \item{col}{color code or name, see \code{\link{par}}.}
  \item{bg}{background (\dQuote{fill}) color for open plot symbols}
  \item{cex}{character expansion: a numerical vector.}
  \item{\dots}{Further graphical parameters (see \code{\link{plot.xy}}
    and \code{\link{par}}) may also be supplied as arguments.}
}
\details{
  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{\link{xy.coords}}.

  Arguments \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.
  Points whose \code{x}, \code{y}, \code{pch}, \code{col} or \code{cex}
  value is \code{NA} are omitted from the plot.

  Graphical parameters are permitted as arguments to this function.
}
\references{
  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
  \emph{The New S Language}.
  Wadsworth \& Brooks/Cole.
}
\seealso{
  \code{\link{plot}}, \code{\link{lines}}, and the underlying
  \dQuote{primitive} \code{\link{plot.xy}}.
}
\examples{
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 ------------
Pex <- 3 ## good for both .Device=="postscript" and "x11"
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 = FALSE, xlab = "", ylab = "",
     main = paste("plot symbols :  points (...  pch = *, cex =", Pex,")"))
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 = 1.2)
}
}
\keyword{aplot}
