legend Add Legends to Plots
Description
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.
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 co-ordinates to be used to position the legend. They can be specified by keyword or in any way which is accepted by |
legend | a character or expression vector of length ≥ 1 to appear in the legend. Other objects will be coerced by |
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 |
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 1-character strings (see |
angle | angle of shading lines. |
density | the density of shading lines, if numeric and positive. If |
bty | the type of box to be drawn around the legend. The allowed values are |
bg | the background color for the legend box. (Note that this is only used if |
box.lty, box.lwd, box.col | the line type, width and color for the legend box (if |
pt.bg | the background color for the |
cex | character expansion factor relative to current |
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 |
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 |
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 |
text.width | the width of the legend text in x ( |
text.col | the color used for the legend text. |
text.font | the font used for the legend text, see |
merge | logical; if |
trace | logical; if |
plot | logical. If |
ncol | the number of columns in which to set the legend items (default is 1, a vertical legend). |
horiz | logical; if |
title | a character string or length-one expression giving a title to be placed at the top of the legend. Other objects will be coerced by |
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 |
title.col | color for |
title.adj | horizontal adjustment for |
seg.len | the length of lines drawn to illustrate |
Details
Arguments x, y, legend are interpreted in a non-standard 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 top-left 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 right-justify 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
rect | a list with components
|
text | a list with components
|
returned invisibly.
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
## 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, length.out = 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")
## right-justifying 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, length.out = 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)
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Licensed under the GNU General Public License.