Customizing Graphs

Base graphics options

plot()• The workhorse plotting function• plot(x) plots values of x in

sequence or a barplot• plot(x, y) produces a scatterplot• plot(y~x, data=data.frame)

produces a scatterplot• Many statistical functions produce

results that can be plotted using plot

Variations on plot()• type = “p”, “l”, “b”, or “n” for

points, lines, both, or no plot (also “c”, “o”, “h”, “s”, “S”)

• asp = sets the y/x aspect ratio (asp=1 for mapping)

• Full control over labels, axes, symbols, lines, etc

Parameter cex=• cex controls the size of text and

symbols in a graph• cex = 1 is the default size (except

for main= where it is 2)• cex.main, cex.sub, cex.lab,

cex.axis control specific parts of the plot

• cex = alone usually controls the size of pch, the plot character

Symbol/Line Styles• pch = (plot character) specifies the

symbol set• cex = symbol size• lty = specifies the line type• lwd = specifies the line thickness

Parameter col=• col = controls the color of a symbol

or line• col.axis, col.lab, col.main, col.sub

control colors of other parts of the graph

• bg = background color• col takes a name or hexadecimal

color value

Color• colors() for list of 657 named

colors• palette() gives the default list of

eight colors• gray() gives grayscale from black -

gray(0) to white – gray(1)

Color Palettes• rainbow(number) generates a

spectrum from red to violet based on hue, saturation, and value (hsv)

• rainbow_hcl(number) similar, but using hue, chroma, and luminance color space (hcl)

• Help pages for these give several other palettes

Fonts• family = sets the font family –

“serif”, “sans”, and “mono” – others may be defined by specific graphic devices

• font = sets the font, 1 plain, 2 bold, 3 italic, 4 bold italic, 5 symbol

• Fonts may be device dependent

Labels• main = “This is the title”,

cex.main, col.main, font.main• sub = “This is the subtitle”,

cex.sub, col.sub, font.sub• Axis labels

– lab = “This is the x-axis label”– ylab = “This is the y-axis label”– cex.lab, col.lab, font.lab, las (0, 1, 2,

3)

Axes• Default usually selects reasonable

axes• xlim, ylim set limits for axes• xaxp, yaxp set tick marks• xlog, ylog to use log scale• xaxt , yaxt “n” suppresses plotting

axis()• Use to add a customized axis or

position an axis on the top or right of the plot or in the margin of the plot

• at = specifies location of tickmarks• labels = specifies labels

Adding to a Graph 1• Plot sets up coordinates• grid – add gridlines• abline – add regression, vertical, or

horizontal lines (full plot window)• points – add points• lines – add lines• segment – add line segments

Adding to a Graph 2• text – add text to plot• legend (locator, position, coords)• arrows – draw arrows• rect – draw rectangles• polygon – draw polygons• ellipse – draw probability ellipse• matlines – draw multiple lines

Margins• Must be set before calling plot• oldpar <- par() # to save current• par(mar= c(bottom, left, top,

right)) if you need more space for labels, titles, etc

Multiple Graphs• par(mfrow=c(rows, cols)) plots in

rows• Par(mfcol=c(rows, cols)) plots in

columns