You can customize many features of your graphs (fonts, colors, axes, titles) through graphic options.

One way is to specify these options in through the par( ) function. If you set parameter values here, the changes will be in effect for the rest of the session or until you change them again. The format is par(optionname=value, optionname=value, ...)

# Set a graphical parameter using par()

par()              # view current settings
opar <- par()      # make a copy of current settings
par(col.lab="red") # red x and y labels
hist(mtcars$mpg)   # create a plot with these new settings
par(opar)          # restore original settings

A second way to specify graphical parameters is by providing the optionname=value pairs directly to a high level plotting function. In this case, the options are only in effect for that specific graph.

# Set a graphical parameter within the plotting function
hist(mtcars$mpg, col.lab="red")

See the help for a specific high level plotting function (e.g. plot, hist, boxplot) to determine which graphical parameters can be set this way.

The remainder of this section describes some of the more important graphical parameters that you can set.

Text and Symbol Size

The following options can be used to control text and symbol size in graphs.

Plotting Symbols

Use the pch= option to specify symbols to use when plotting points. For symbols 21 through 25, specify border color (col=) and fill color (bg=).

Lines

You can change lines using the following options. This is particularly useful for reference lines, axes, and fit lines.

Colors

Options that specify colors include the following.

You can specify colors in R by index, name, hexadecimal, or RGB.
For example col=1, col="white", and col="#FFFFFF" are equivalent.

The following chart was produced with code developed by Earl F. Glynn. See his Color Chart for all the details you would ever need about using colors in R.

You can also create a vector of n contiguous colors using the functions rainbow(n), heat.colors(n), terrain.colors(n), topo.colors(n), and cm.colors(n).

colors() returns all available color names.

Fonts

You can easily set font size and style, but font family is a bit more complicated.

In windows, mono is mapped to "TT Courier New", serif is mapped to"TT Times New Roman", sans is mapped to "TT Arial", mono is mapped to "TT Courier New", and symbol is mapped to "TT Symbol" (TT=True Type). You can add your own mappings.

# Type family examples - creating new mappings
plot(1:10,1:10,type="n")
windowsFonts(
 A=windowsFont("Arial Black"),
  B=windowsFont("Bookman Old Style"),
  C=windowsFont("Comic Sans MS"),
  D=windowsFont("Symbol")
)
text(3,3,"Hello World Default")
text(4,4,family="A","Hello World from Arial Black")
text(5,5,family="B","Hello World from Bookman Old Style")
text(6,6,family="C","Hello World from Comic Sans MS")
text(7,7,family="D", "Hello World from Symbol")

click to view

Margins and Graph Size

You can control the margin size using the following parameters.

For complete information on margins, see Earl F. Glynn's margin tutorial.

Axes and Text

Many high level plotting functions (plot, hist, boxplot, etc.) allow you to include axis and text options (as well as other graphical parameters). For example

# Specify axis options within plot()
plot(x, y, main="title", sub="subtitle",
  xlab="X-axis label", ylab="y-axix label",
  xlim=c(xmin, xmax), ylim=c(ymin, ymax))

For finer control or for modularization, you can use the functions described below.

Titles

Use the title( ) function to add labels to a plot.

title(main="main title", sub="sub-title",
   xlab="x-axis label", ylab="y-axis label")

Many other graphical parameters (such as text size, font, rotation, and color) can also be specified in the title( ) function.

# Add a red title and a blue subtitle. Make x and y
# labels 25% smaller than the default and green.
title(main="My Title", col.main="red",
  sub="My Sub-title", col.sub="blue",
  xlab="My X label", ylab="My Y label",
  col.lab="green", cex.lab=0.75)

Text Annotations

Text can be added to graphs using the text( ) and mtext( ) functions. text( ) places text within the graph while mtext( ) places text in one of the four margins.

(To practice adding text to plots in R, try this interactive exercise.)

text(location, "text to place", pos, ...)
mtext("text to place", side, line=n, ...)

Common options are described below.

Other common options are cex, col, and font (for size, color, and font style respectively).

Labeling points

You can use the text( ) function (see above) for labeling point as well as for adding other text annotations. Specify location as a set of x, y coordinates and specify the text to place as a vector of labels. The x, y, and label vectors should all be the same length.

# Example of labeling points
attach(mtcars)
plot(wt, mpg, main="Milage vs. Car Weight",
   xlab="Weight", ylab="Mileage", pch=18, col="blue")
text(wt, mpg, row.names(mtcars), cex=0.6, pos=4, col="red")

click to view

Math Annotations

You can add mathematically formulas to a graph using TEX-like rules. See help(plotmath) for details and examples.

Axes

You can create custom axes using the axis( ) function.

axis(side, at=, labels=, pos=, lty=, col=, las=, tck=, ...)

where

If you are going to create a custom axis, you should suppress the axis automatically generated by your high level plotting function. The option axes=FALSE suppresses both x and y axes. xaxt="n" and yaxt="n" suppress the x and y axis respectively. Here is a (somewhat overblown) example.

# A Silly Axis Example

# specify the data
x <- c(1:10); y <- x; z <- 10/x

# create extra margin room on the right for an axis
par(mar=c(5, 4, 4, 8) + 0.1)

# plot x vs. y
plot(x, y,type="b", pch=21, col="red",
   yaxt="n", lty=3, xlab="", ylab="")

# add x vs. 1/x
lines(x, z, type="b", pch=22, col="blue", lty=2)

# draw an axis on the left
axis(2, at=x,labels=x, col.axis="red", las=2)

# draw an axis on the right, with smaller text and ticks
axis(4, at=z,labels=round(z,digits=2),
  col.axis="blue", las=2, cex.axis=0.7, tck=-.01)

# add a title for the right axis
mtext("y=1/x", side=4, line=3, cex.lab=1,las=2, col="blue")

# add a main title and bottom and left axis labels
title("An Example of Creative Axes", xlab="X values",
   ylab="Y=X")

click to view

Minor Tick Marks

The minor.tick( ) function in the Hmisc package adds minor tick marks.

# Add minor tick marks
library(Hmisc)
minor.tick(nx=n, ny=n, tick.ratio=n)

nx is the number of minor tick marks to place between x-axis major tick marks.
ny does the same for the y-axis. tick.ratio is the size of the minor tick mark relative to the major tick mark. The length of the major tick mark is retrieved from par("tck").

Reference Lines

Add reference lines to a graph using the abline( ) function.

abline(h=yvalues, v=xvalues)

Other graphical parameters (such as line type, color, and width) can also be specified in the abline( ) function.

# add solid horizontal lines at y=1,5,7
abline(h=c(1,5,7))
# add dashed blue verical lines at x = 1,3,5,7,9
abline(v=seq(1,10,2),lty=2,col="blue")

Note: You can also use the grid( ) function to add reference lines.

Legend

Add a legend with the legend() function.

legend(location, title, legend, ...)

Common options are described below.

Other common legend options include bty for box type, bg for background color, cex for size, and text.col for text color. Setting horiz=TRUE sets the legend horizontally rather than vertically.

# Legend Example
attach(mtcars)
boxplot(mpg~cyl, main="Milage by Car Weight",
   yaxt="n", xlab="Milage", horizontal=TRUE,
   col=terrain.colors(3))
legend("topright", inset=.05, title="Number of Cylinders",
   c("4","6","8"), fill=terrain.colors(3), horiz=TRUE)

click to view

For more on legends, see help(legend). The examples in the help are particularly informative.