points
Add Points to a Plot
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.
- Keywords
- aplot
Usage
points(x, …)# S3 method for default
points(x, y = NULL, type = "p", …)
Arguments
- x, y
coordinate vectors of points to plot.
- type
character indicating the type of plotting; actually any of the
types as inplot.default.- …
Further graphical parameters may also be supplied as arguments. See ‘Details’.
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. If supplied
separately, they must be of the same length.
Graphical parameters commonly used are
pchplotting ‘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
pch = 0:18, see the examples below. (NB: R uses circles instead of the octagons used in S.)Value
pch = "."(equivalentlypch = 46) is handled specially. It is a rectangle of side 0.01 inch (scaled bycex). In addition, ifcex = 1(the default), each side is at least one pixel (1/72 inch on thepdf,postscriptandxfigdevices).For other text symbols,
cex = 1corresponds to the default fontsize of the device, often specified by an argumentpointsize. Forpchin0:25the default size is about 75% of the character height (seepar("cin")).colcolor code or name, see
par.bgbackground (fill) color for the open plot symbols given by
pch = 21:25.cexcharacter (or symbol) expansion: a numerical vector. This works as a multiple of
par("cex").lwdline width for drawing symbols see
par.
Others less commonly used are lty and lwd for
types such as "b" and "l".
The graphical parameters pch, col, bg,
cex and 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 type = "b") the first element of lwd
is used.
Points whose x, y, pch, col or cex
value is NA are omitted from the plot.
Note
A single-byte encoding may include the characters in
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 code points, and no check is done. A display device is likely to use a rectangle for (or omit) Unicode code points which are invalid or for which it does not have a glyph in the font used.
What happens for very small or zero values of cex is
device-dependent: symbols or characters may become invisible or
they may be plotted at a fixed minimum size. Circles of zero radius
will not be plotted.
'pch' values
Values of pch are stored internally as integers. The
interpretation is
NA_integer_: no symbol.0:18: S-compatible vector symbols.19:25: further R vector symbols.26:31: unused (and ignored).32:127: ASCII characters.128:255native characters only in a single-byte locale and for the symbol font. (128:159are only used on Windows.)-32 …Unicode code point (where supported).
Note that unlike S (which uses octagons), symbols 1, 10,
13 and 16 use circles. The filled shapes 15:18
do not include a border.
The following R plotting symbols are can be obtained with
pch = 19:25: those with 21:25 can be colored and
filled with different colors: col gives the border color
and bg the background color
(which is "grey" in the figure)
pch = 19: solid circle,pch = 20: bullet (smaller solid circle, 2/3 the size of19),pch = 21: filled circle,pch = 22: filled square,pch = 23: filled diamond,pch = 24: filled triangle point-up,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 pdf).
The difference between pch = 16 and pch = 19 is that the
latter uses a border and so is perceptibly larger when lwd is
large relative to cex.
Values pch = 26:31 are currently unused and pch = 32:127
give the ASCII characters. In a single-byte locale
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 code point, so e.g.-0x2642L
is a ‘male sign’ and -0x20ACL is the Euro.
A character string consisting of a single character is converted to an
integer: 32:127 for ASCII characters, and usually to the
Unicode code point otherwise. (In non-Latin-1 single-byte locales,
128:255 will be used for 8-bit characters.)
If pch supplied is a logical, integer or character
NA or an empty character string the point is omitted from
the plot.
If pch is NULL or otherwise of length 0,
par("pch") is used.
If the symbol font (par(font = 5)) is used, numerical
values should be used for pch: the range is
c(32:126, 160:254) in all locales (but 240 is not
defined (used for ‘apple’ on macOS) and 160, Euro, may
not be present).
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
points.formula for the formula method;
plot, lines, and the underlying
workhorse function plot.xy.
Examples
library(graphics)
# NOT RUN {
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)
# }
# NOT RUN {
## The figure was produced by calls like
png("pch.png", height = 0.7, width = 7, res = 100, units = "in")
par(mar = rep(0,4))
plot(c(-1, 26), 0:1, type = "n", axes = FALSE)
text(0:25, 0.6, 0:25, cex = 0.5)
points(0:25, rep(0.3, 26), pch = 0:25, bg = "grey")
# }
# NOT RUN {
##-------- 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)
# }
# NOT RUN {
## ------------ 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, ...)
{
MB <- l10n_info()$MBCS
r <- if(font == 5) { sign <- 1; c(32:126, 160:254)
} else if(MB) 32:126 else 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",
main = sprintf("sign = %d, font = %d", sign, font))
grid(17, 17, lty = 1) ; mtext(paste("MBCS:", MB))
for(i in r) try(points(i%%16, i%/%16, pch = sign*i, font = font,...))
}
TestChars()
try(TestChars(sign = -1))
TestChars(font = 5) # Euro might be at 160 (0+10*16).
# macOS has apple at 240 (0+15*16).
try(TestChars(-1, font = 2)) # bold
# }