legend: Add Legends to Plots

Description

This is a modified version of legend() in the base package, which allows for printing spectra of colours in the legend, as used in this package. 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,
       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.

bty

the type of box to be drawn around the legend.

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).

Value

A (invisible) list with list components
recta list with components [object Object],[object Object]
texta list with components [object Object]

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.

Examples

Run this code

## 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))

## 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 = "*")
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")

## 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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