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 = 1, pch,
       bty = "o", bg = par("bg"), cex = 1, xjust = 0, yjust = 1,
       x.intersp = 1, y.intersp = 1, adj = 0,
       text.width = NULL, merge = do.lines && has.pch)

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 >= 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.
bty the type of box to be drawn around the legend.
bg the background color for the legend box.
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.

Details

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

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(.9,  y.leg[i], paste("cex=",formatC(cexv[i])),srt=90,adj=1, cex=.7)
  legend(1, 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=T)#, trace=T)
}
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
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))
legend(4.1, 30, ex12, col = 2:3, lty=2:3, lwd=2)
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