legend
Add Legends to Plots
This function can be used to add legends to plots. Note that a call
to the function locator(1)
can be used in place of the x
and y
arguments.
 Keywords
 aplot
Usage
legend(x, y = NULL, legend, fill = NULL, col = par("col"),
border = "black", lty, lwd, pch,
angle = 45, density = NULL, bty = "o", bg = par("bg"),
box.lwd = par("lwd"), box.lty = par("lty"), box.col = par("fg"),
pt.bg = NA, cex = 1, pt.cex = cex, pt.lwd = lwd,
xjust = 0, yjust = 1, x.intersp = 1, y.intersp = 1,
adj = c(0, 0.5), text.width = NULL, text.col = par("col"),
text.font = NULL, merge = do.lines && has.pch, trace = FALSE,
plot = TRUE, ncol = 1, horiz = FALSE, title = NULL,
inset = 0, xpd, title.col = text.col, title.adj = 0.5,
seg.len = 2)
Arguments
 x, y
the x and y coordinates to be used to position the legend. They can be specified by keyword or in any way which is accepted by
xy.coords
: See ‘Details’. legend
a character or expression vector of length \(\ge 1\) to appear in the legend. Other objects will be coerced by
as.graphicsAnnot
. fill
if specified, this argument will cause boxes filled with the specified colors (or shaded in the specified colors) to appear beside the legend text.
 col
the color of points or lines appearing in the legend.
 border
the border color for the boxes (used only if
fill
is specified). 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, as numeric vector or a vector of 1character strings (see
points
). Unlikepoints
, this can all be specified as a single multicharacter string. Must be specified for symbol drawing. angle
angle of shading lines.
 density
the density of shading lines, if numeric and positive. If
NULL
or negative orNA
color filling is assumed. bty
the type of box to be drawn around the legend. The allowed values are
"o"
(the default) and"n"
. bg
the background color for the legend box. (Note that this is only used if
bty != "n"
.) box.lty, box.lwd, box.col
the line type, width and color for the legend box (if
bty = "o"
). pt.bg
the background color for the
points
, corresponding to its argumentbg
. cex
character expansion factor relative to current
par("cex")
. Used for text, and provides the default forpt.cex
. pt.cex
expansion factor(s) for the points.
 pt.lwd
line width for the points, defaults to the one for lines, or if that is not set, to
par("lwd")
. 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 yadjustment when
labels
are plotmath expressions. text.width
the width of the legend text in x (
"user"
) coordinates. (Should be a single positive number even for a reversed x axis.) Defaults to the proper value computed bystrwidth(legend)
. text.col
the color used for the legend text.
 text.font
the font used for the legend text, see
text
. merge
logical; if
TRUE
, merge points and lines but not filled boxes. Defaults toTRUE
if there are points and lines. trace
logical; if
TRUE
, shows howlegend
does all its magical computations. plot
logical. If
FALSE
, nothing is plotted but the sizes are returned. 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 (specifyinghoriz
overrides thencol
specification). title
a character string or lengthone expression giving a title to be placed at the top of the legend. Other objects will be coerced by
as.graphicsAnnot
. inset
inset distance(s) from the margins as a fraction of the plot region when legend is placed by keyword.
 xpd
if supplied, a value of the graphical parameter
xpd
to be used while the legend is being drawn. title.col
color for
title
. title.adj
horizontal adjustment for
title
: see the help forpar("adj")
. seg.len
the length of lines drawn to illustrate
lty
and/orlwd
(in units of character widths).
Details
Arguments x
, y
, legend
are interpreted in a
nonstandard way to allow the coordinates to be specified via
one or two arguments. If legend
is missing and y
is not
numeric, it is assumed that the second argument is intended to be
legend
and that the first argument specifies the coordinates.
The coordinates can be specified in any way which is accepted by
xy.coords
. If this gives the coordinates of one point,
it is used as the topleft coordinate of the rectangle containing the
legend. If it gives the coordinates of two points, these specify
opposite corners of the rectangle (either pair of corners, in any
order).
The location may also be specified by setting x
to a single
keyword from the list "bottomright"
, "bottom"
,
"bottomleft"
, "left"
, "topleft"
,
"top"
, "topright"
, "right"
and
"center"
. This places the legend on the inside of the plot
frame at the given location. Partial argument matching is used. The
optional inset
argument specifies how far the legend is inset
from the plot margins. If a single value is given, it is used for
both margins; if two values are given, the first is used for x

distance, the second for y
distance.
Attribute arguments such as col
, pch
, lty
, etc,
are recycled if necessary: merge
is not. Set entries of
lty
to 0
or set entries of lwd
to NA
to
suppress lines in corresponding legend entries; set pch
values to NA
to suppress points.
Points are drawn after lines in order that they can cover the
line with their background color pt.bg
, if applicable.
See the examples for how to rightjustify labels.
Since they are not used for Unicode code points, values 31:1
are silently omitted, as are NA
and ""
values.
Value
A list with list components
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.
a list with components
x, y
numeric vectors of length
length(legend)
, giving the x and y coordinates of the legend's text(s).
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Murrell, P. (2005) R Graphics. Chapman & Hall/CRC Press.
See Also
plot
, barplot
which uses legend()
, and
text
for more examples of math expressions.
Examples
library(graphics)
# NOT RUN {
## 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]  0.1, paste("cex=", formatC(cexv[i])), cex = 0.8, adj = 0)
legend(3, y.leg[i], leg.txt, pch = "sSvV", col = c(1, 3), cex = cexv[i])
}
## cex *vector* [in R <= 3.5.1 has 'if(xc < 0)' w/ length(xc) == 2]
legend(6,1, leg.txt, pch = "sSvV", col = c(1, 3), cex = 1+(1:2)/8)
## '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(NA, 3, 4), merge = TRUE)",
cex.main = 1.1)
legend(1, 1.9, c("sin", "cos", "tan"), col = c(3, 4, 6),
text.col = "green4", lty = c(2, 1, 1), pch = c(NA, 3, 4),
merge = TRUE, bg = "gray90")
## rightjustifying a set of labels: thanks to Uwe Ligges
x < 1:5; y1 < 1/x; y2 < 2/x
plot(rep(x, 2), c(y1, y2), type = "n", xlab = "x", ylab = "y")
lines(x, y1); lines(x, y2, lty = 2)
temp < legend("topright", legend = c(" ", " "),
text.width = strwidth("1,000,000"),
lty = 1:2, xjust = 1, yjust = 1,
title = "Line Types")
text(temp$rect$left + temp$rect$w, temp$text$y,
c("1,000", "1,000,000"), pos = 2)
## 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 = paste0("log = '", ll, "'"))
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, 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: 
x < seq(pi, pi, len = 65)
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
utils::str(legend(3, .9, ex.cs1, lty = 1:2, plot = FALSE,
adj = c(0, 0.6))) # adj y !
legend(3, 0.9, ex.cs1, lty = 1:2, col = 2:3, adj = c(0, 0.6))
require(stats)
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))
utils::str(legend(4.1, 30, ex12, col = 2:3, lty = 2:3, lwd = 2))
## 'Filled' boxes  for more, see example(plot.factor)
op < par(bg = "white") # to get an opaque box for the legend
plot(cut(weight, 3) ~ group, data = PlantGrowth, col = NULL,
density = 16*(1:3))
par(op)
## 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 = 0.8)
legend(.8,1.2, paste("sin(", 1:7, "pi * x)"), col = 1:7, lty = 1:7,
pch = "*", cex = 0.8)
legend(0, .1, paste("sin(", 1:4, "pi * x)"), col = 1:4, lty = 1:4,
ncol = 2, cex = 0.8)
legend(0, .4, paste("sin(", 5:7, "pi * x)"), col = 4:6, pch = 24,
ncol = 2, cex = 1.5, lwd = 2, pt.bg = "pink", pt.cex = 1:3)
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")
## legends with titles at different locations
plot(x, y, type = "n")
legend("bottomright", "(x,y)", pch=1, title= "bottomright")
legend("bottom", "(x,y)", pch=1, title= "bottom")
legend("bottomleft", "(x,y)", pch=1, title= "bottomleft")
legend("left", "(x,y)", pch=1, title= "left")
legend("topleft", "(x,y)", pch=1, title= "topleft, inset = .05", inset = .05)
legend("top", "(x,y)", pch=1, title= "top")
legend("topright", "(x,y)", pch=1, title= "topright, inset = .02",inset = .02)
legend("right", "(x,y)", pch=1, title= "right")
legend("center", "(x,y)", pch=1, title= "center")
# using text.font (and text.col):
op < par(mfrow = c(2, 2), mar = rep(2.1, 4))
c6 < terrain.colors(10)[1:6]
for(i in 1:4) {
plot(1, type = "n", axes = FALSE, ann = FALSE); title(paste("text.font =",i))
legend("top", legend = LETTERS[1:6], col = c6,
ncol = 2, cex = 2, lwd = 3, text.font = i, text.col = c6)
}
par(op)
# }