\HeaderA{points}{Add Points to a Plot}{points}
\aliasA{pch}{points}{pch}
\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 \sQuote{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}}.  If supplied
separately, they must be of the same length.

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 examples below.

Value \code{pch="."} (equivalently \code{pch = 46}) 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).

For other text symbols, \code{cex = 1} corresponds to the default
fontsize of the device, often specified by an argument
\code{pointsize}.  For \code{pch} in \code{0:25} the default size
is about 75\% of the character height (see \code{par("cin")}).

\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{Section}{'pch' values}
Values of \code{pch} are stored internally as integers.  The
interpretation is
\Itemize{
\item \code{NA\_integer\_}: no symbol.
\item \code{0:18}: S-compatible vector symbols.
\item \code{19:25}: further \R{} vector symbols.
\item \code{26:31}: unused (and ignored).
\item \code{32:127}: ASCII characters.
\item \code{128:255} native characters \emph{only in a
single-byte locale and for the symbol font}.  (\code{128:159} are
only used on Windows.)
\item \code{-32 ...} Unicode point (where supported).
}
Note that unlike S (which uses octagons), symbols \code{1}, \code{10},
\code{13} and \code{16} use circles.  The filled shapes \code{15:18}
do not include a border.

The following  \R{} plotting symbols are can be obtained with
\code{pch=19:25}: those with \code{21:25} can be colored and
filled with different colors: \code{col} gives the border color
and \code{bg} the background color.
\Itemize{
\item \code{pch=19}: solid circle,
\item \code{pch=20}: bullet (smaller solid circle, 2/3 the size of 19),
\item \code{pch=21}: filled circle,
\item \code{pch=22}: filled square,
\item \code{pch=23}: filled diamond,
\item \code{pch=24}: filled triangle point-up,
\item \code{pch=25}: filled triangle point down.
}
Note that all of these both fill the shape and draw a border.  Some
care in interpretation is needed when semi-transparent colours are
used for both fill and border (and the result might be device-specific
and even viewer-specific for \code{\LinkA{pdf}{pdf}}).

The difference between \code{pch=16} and \code{pch=19} is that the
latter uses a border and so is perceptibly larger when \code{lty} is
large relative to \code{cex}.

Values \code{pch=26:31} are currently unused and \code{pch=32:127}
give the ASCII characters.  In a single-byte locale
\code{pch=128:255} give the corresponding character (if any) in
the locale's character set.  Where supported by the OS, negative
values specify a Unicode point, so e.g. \code{-0x2642L}
is a \sQuote{male sign} and \code{-0x20ACL} is the Euro.

A character string consisting of a single character is converted to an
integer: \code{32:127} for ASCII characters, and usually to the
Unicode point number otherwise.  (In non-Latin-1 single-byte locales,
\code{128:255} will be used for 8-bit characters.)

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

If \code{pch} is \code{NULL} or otherwise of length 0,
\code{par("pch")} is used.

If the symbol font (\code{\LinkA{par}{par}(font = 5)}) is used, numerical
values should be used for \code{pch}: the range is
\code{c(32:126, 160:254)} in all locales (but \code{240} is not
defined (used for \sQuote{apple} on Mac OS) and \code{160}, Euro, may
not be present).
\end{Section}
\begin{Note}\relax
A single-byte encoding may include the characters in
\code{pch=128:255}, and if it does, a font may not include all (or
even any) of them.

Not all negative numbers are valid as Unicode points, and no check is
done.  A display device is likely to use a rectangle for (or omit)
Unicode points that do not exist or which it does not have a glyph.
\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] - 0.3, iy[i], pc, col = coltext, cex = cextext)
    }
  }

pchShow()
pchShow(c("o","O","0"), cex = 2.5)
pchShow(NULL, cex = 4, cextext = 0, main = NULL)


## ------------ test code for various pch specifications -------------
# Try this in various font families (including Hershey)
# and locales.  Use sign=-1 asserts we want Latin-1.
# Standard cases in a MBCS locale will not plot the top half.
TestChars <- function(sign=1, font=1, ...)
{
   if(font == 5) { sign <- 1; r <- c(32:126, 160:254)
   } else if (l10n_info()$MBCS) r <- 32:126 else r <- 32:255
   if (sign == -1) r <- c(32:126, 160:255)
   par(pty="s")
   plot(c(-1,16), c(-1,16), type="n", xlab="", ylab="",
        xaxs="i", yaxs="i")
   grid(17, 17, lty=1)
   for(i in r) try(points(i%%16, i%/%16, pch=sign*i, font=font,...))
}
TestChars()
try(TestChars(sign=-1)) # needs MBCS support
TestChars(font=5) # Euro might be at 160.  Mac OS has apple at 240.
\end{ExampleCode}
\end{Examples}

