R: Add Points to a Plot

points {graphics}

R Documentation

Add Points to a Plot

Description

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, ...)

## Default S3 method:
points(x, y = NULL, type = "p", pch = par("pch"),
       col = par("col"), bg = NA, cex = 1, ...)

Arguments

x, y

coordinate vectors of points to plot.

type

character indicating the type of plotting; actually any of the types as in plot.

pch

plotting “character”, i.e., symbol to use. pch 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 pch=0:18, see the last picture from example(points), i.e., the examples below.

In addition, there is a special set of R plotting symbols which can be obtained with pch=19:25 and 21:25 can be colored and filled with different colors:

pch=19: solid circle,
pch=20: bullet (smaller circle),
pch=21: circle,
pch=22: square,
pch=23: diamond,
pch=24: triangle point-up,
pch=25: triangle point down.

Values pch=26:32 are currently unused, and pch=32:255 give the text symbol in a single-byte locale. In a multi-byte locale such as UTF-8, numeric values of pch greater than or equal to 32 specify a Unicode code point.

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

Value pch="." is handled specially. It is a rectangle of side 0.01 inch (scaled by cex). In addition, if cex = 1 (the default), each side is at least one pixel (1/72 inch on the pdf, postscript and xfig devices). The details here have been changed for 2.1.0 and are subject to change.

col

color code or name, see par.

bg

background (“fill”) color for open plot symbols

cex

character (or symbol) expansion: a numerical vector.

...

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

Details

The coordinates can be passed in a plotting structure (a list with x and y components), a two-column matrix, a time series, .... See xy.coords.

Arguments pch, col, bg, cex and lwd can be vectors (which will be recycled as needed) giving a value for each point plotted. Points whose x, y, pch, col or cex value is NA are omitted from the plot.

Graphical parameters are permitted as arguments to this function.

Note

What is meant by ‘a single character’ is locale-dependent.

The encoding may not have symbols for some or all of the characters in pch=128:255

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth \& Brooks/Cole.

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)
}

[Package graphics version 2.1.1 ]