legend {base}

R Documentation

Add Legends to Plots

Description

This function can be used to add legends to plots. Note that a call to the function locator can be used in place of the x and y arguments.

Usage

legend(x, y, legend, fill, col = "black", lty, lwd, pch,
       angle = NULL, density = NULL,
       bty = "o", bg = par("bg"), pt.bg = NA, cex = 1, xjust = 0, yjust = 1,
       x.intersp = 1, y.intersp = 1, adj = 0,
       text.width = NULL, merge = do.lines && has.pch, trace = FALSE,
       ncol = 1, horiz = FALSE)

Arguments

x, y	the x and y location of the legend. x can be a list with x and y components.
legend	a vector of text values or an expression of length \ge 1 to appear in the legend.
fill	if specified, this argument will cause boxes filled with the specified colors to appear beside the legend text.
col	the color of points or lines appearing in the legend.
lty, lwd	the line types and widths for lines appearing in the legend. One of these two must be specified for line drawing.
pch	the plotting symbols appearing in the legend, either as vector of 1-character strings, or one (multi character) string. Must be specified for symbol drawing.
angle	angle of shading lines.
density	the density of shading lines, if numeric and positive.
bty	the type of box to be drawn around the legend.
bg	the background color for the legend box.
pt.bg	the background color for the points.
cex	character expansion factor relative to current par("cex").
xjust	how the legend is to be justified relative to the legend x location. A value of 0 means left justified, 0.5 means centered and 1 means right justified.
yjust	the same as xjust for the legend y location.
x.intersp	character interspacing factor for horizontal (x) spacing.
y.intersp	the same for vertical (y) line distances.
adj	numeric of length 1 or 2; the string adjustment for legend text. Useful for y-adjustment when labels are plotmath expressions.
text.width	the width of the legend text in x ("user") coordinates. Defaults to the proper value computed by strwidth(legend).
merge	logical; if TRUE, “merge” points and lines but not filled boxes. Defaults to TRUE if there are points and lines.
trace	logical; if TRUE, shows how legend does all its magical computations.
ncol	the number of columns in which to set the legend items (default is 1, a vertical legend).
horiz	logical; if TRUE, set the legend horizontally rather than vertically (specifying horiz overrides the ncol specification).

Details

“Attribute” arguments such as col, pch, lty, etc, are recycled if necessary. merge is not.

Points are drawn after lines in order that they can cover the line with their background color pt.bg, if applicable.

Value

A (invisible) list with list components

rect	a list with components w,h positive numbers giving width and height of the legend's box. left,top x and y coordinates of upper left corner of the box.
text	a list with components x,y numeric vectors of length length(legend), giving the x and y coordinates of the legend's text(s).

See Also

plot, barplot which uses legend(), and text for more examples of math expressions.

Examples

## Run the example in `?matplot' or the following:
leg.txt <- c("Setosa     Petals", "Setosa     Sepals",
             "Versicolor Petals", "Versicolor Sepals")
y.leg <- c(4.5, 3, 2.1, 1.4, .7)
cexv  <- c(1.2, 1, 4/5, 2/3, 1/2)
matplot(c(1,8), c(0,4.5), type = "n", xlab = "Length", ylab = "Width",
        main = "Petal and Sepal Dimensions in Iris Blossoms")
for (i in seq(cexv)) {
  text  (1, y.leg[i]-.1, paste("cex=",formatC(cexv[i])), cex=.8, adj = 0)
  legend(3, y.leg[i], leg.txt, pch = "sSvV", col = c(1, 3), cex = cexv[i])
}
## `merge = TRUE' for merging lines & points:
x <- seq(-pi, pi, len = 65)
plot(x, sin(x), type = "l", ylim = c(-1.2, 1.8), col = 3, lty = 2)
points(x, cos(x), pch = 3, col = 4)
lines(x, tan(x), type = "b", lty = 1, pch = 4, col = 6)
title("legend(..., lty = c(2, -1, 1), pch = c(-1,3,4), merge = TRUE)",
      cex.main = 1.1)
legend(-1, 1.9, c("sin", "cos", "tan"), col = c(3,4,6),
       lty = c(2, -1, 1), pch = c(-1, 3, 4), merge = TRUE, bg='gray90')

##--- log scaled Examples ------------------------------
leg.txt <- c("a one", "a two")

par(mfrow = c(2,2))
for(ll in c("","x","y","xy")) {
  plot(2:10, log=ll, main=paste("log = '",ll,"'", sep=""))
  abline(1,1)
  lines(2:3,3:4, col=2) #
  points(2,2, col=3)    #
  rect(2,3,3,2, col=4)
  text(c(3,3),2:3, c("rect(2,3,3,2, col=4)",
                     "text(c(3,3),2:3,\"c(rect(...)\")"), adj = c(0,.3))
  legend(list(x=2,y=8), legend = leg.txt, col=2:3, pch=1:2,
         lty=1, merge=TRUE)#, trace=TRUE)
}
par(mfrow=c(1,1))

##-- Math expressions:  ------------------------------
plot(x, sin(x), type="l", col = 2,xlab=expression(phi),ylab=expression(f(phi)))
abline(h=-1:1, v=pi/2*(-6:6), col="gray90")
lines(x, cos(x), col = 3, lty = 2)
ex.cs1 <- expression(plain(sin) * phi,  paste("cos", phi))# 2 ways
str(legend(-3, .9, ex.cs1, lty=1:2, col=2:3, adj = c(0, .6)))# adj y !

x <- rexp(100, rate = .5)
hist(x, main = "Mean and Median of a Skewed Distribution")
abline(v = mean(x),   col=2, lty=2, lwd=2)
abline(v = median(x), col=3, lty=3, lwd=2)
ex12 <- expression(bar(x) == sum(over(x[i], n), i==1, n),
                   hat(x) == median(x[i], i==1,n))
str(legend(4.1, 30, ex12, col = 2:3, lty=2:3, lwd=2))

## `Filled' boxes -- for more, see example(plotfactor)
data(PlantGrowth)
plot(cut(weight, 3) ~ group, data = PlantGrowth,
     col = NULL, density = 16*(1:3))

## Using `ncol' :
x <- 0:64/64
matplot(x, outer(x, 1:7, function(x, k) sin(k * pi * x)),
        type = "o", col = 1:7, ylim = c(-1, 1.5), pch = "*")
op <- par(bg="antiquewhite1")
legend(0, 1.5, paste("sin(",1:7,"pi * x)"), col=1:7, lty=1:7, pch = "*",
       ncol = 4, cex=.8)
legend(.8,1.2, paste("sin(",1:7,"pi * x)"), col=1:7, lty=1:7, pch = "*",cex=.8)
legend(0, -.1, paste("sin(",1:4,"pi * x)"), col=1:4, lty=1:4, ncol=2, cex=.8)
legend(0, -.4, paste("sin(",5:7,"pi * x)"), col=5:7,  pch=24, ncol=2, cex=1.5,
       pt.bg="pink")
par(op)

## point covering line :
y <- sin(3*pi*x)
plot(x,y,type="l",col="blue", main = "points with bg & legend(*, pt.bg)")
points(x,y,pch=21,bg="white")
legend(.4,1,"sin(c x)",pch=21,pt.bg="white",lty=1, col = "blue")

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