Graphical Parameters

The following arguments can be specified within any graphical function to specify titles, where string is the title inserted in quotes, or a character vector containing the title:

main="string"

main title, above plot, in enlarged characters

sub="string"

sub-title for bottom of plot

main="# of chin ups \n Females"

for titles and sub-titles to run over more than one line, use \n in the character string to start a new line

xlab="string", ylab="string"

labels for the x an y axes

axes=

logical flag specifying axes=F forces Splus to omit drawing the axes

xlim=, ylim=

vectors giving the min and max values for the x and y axes

Splus may extend the axes further to produce pretty tick labels

log=

specifies the axes to be logarithmic (ie.: log="xy")

type=

type of plot:

• "p" points
• "l" lines
• "b" both
• "o" both - overstruck
• "h" high density
• "n" null (sets up the axes to be filled in later)

> par(mfrow=c(2,3))
                       * it is possible to specify the number and
                         arrangement of graphs on a page using the
                         mfrow= option
                       * mfrow=c(2,3) allows 6 plots to appear on
                         a page (2 rows of 6 plots each)
                       * because the mfrow argument was used within
                         the par function, the set up will stay in effect 
                         for all subsequent graphs

> par(mfrow=c(1,1))    
                       * restores the normal one-graph-per-page form
                       * this could also be done by invoking a new
                         graphic device
                         > X11()
> par(mfcol=c(3,2))    
                       * the page is set up as above except that the
                         graphs are printed columnwise, mfrow prints
                         graphs row by row

pch=

plotting character, the default is pch="*"

it is possible to specify either a character, using quotes, or a numeric value, causing Splus to use one of a set of predefined values:

   Basic symbols            Superimposed symbols        Filled in symbols

   0  square                    7  0 and 4                15  square
   1  octagon                   8  3 and 4                16  octagon
   2  triangle                  9  3 and 5                17  triangle
   3  cross                    10  1 and 3                18  diamond
   4  X                        11  2 and 6
   5  diamond                  12  0 and 3
   6  inverted triangle        13  1 and 4
                               14  0 and 2

cex=

character expansion, ie.: cex=0.5 gives half the standard character size

lty=

line type: a value of 1 gives solid lines, values of 2,3... will select a non-solid line type

lwd=

line width: the default value is 1. Increasing values produce thicker lines

col=

numeric color specification (default is 1)

adj=

string justification:

• 0 left justify
• 1 right justify
• 0.5 centre
• or any other fraction

oma=

a vector specifying the margins on each of the four sides of a multiple figure region:

c(bottom, left, top, right)

where the values specified are the number of lines of text

ask=

logical value

ask=T means graphical device will prompt before going to the next page/screen of output (prevents plots from being erased before they are studied)

lab=

controls number of tick intervals and length of labels

• x= number of tick intervals on x axis (default = 5)
• y= number of tick intervals on y axis (default = 5)
• llen= length of labels on both axes (default = 7)
• eg.: lab=c(x=6, y=4, llen=9)

las=

type of axis labels:

0 parallel to axis

1 horizontal

2 perpendicular to axis

Other Useful FUnctions

points(x,y,pch= )

the function points() allows you to add variables to the current plot

lines(x,y,lty= )

the function lines() allows you to add lines to the current plot

abline

adds a line to a plot

arguments can be specified as:

• (a,b) where a = intercept and b = slope
• (coef) vector containing the intercept a and slope b
• (reg) a regression object
• (h= ) vector of y-coordinates for horizontal lines
• (v= ) vector of x-coordinates for vertical lines

legend(x,y,legend= )

puts a box at the specified x,y coordinates with examples (if possible) of the lines/points/shading used in the graph identified by user-defined text

identify(x,y,labels= )

similar to legend(), identify() prints text (labels) at the specified points

locator(n= ,type= )

returns the coordinates specified interactively on a plot

default is n=500, type="n"

by changing type, points and/or lines may be added to the plot

the locator() function can be used within the function legend() or identify() instead of specifying the x and y coordinates: legend(locator(1),legend)

the point is identified by placing the cursor over the point and pressing the left mouse button

to exit locator without identifying all "n" points, press the middle mouse button

title(main= , sub= , xlab= , ylab= )

adds titles and/or axis labels to the current plot

will overwrite any existing titles and/or axis labels

segments(x1,y1,x2,y2)

adds a line segment with endpoints (x1,y1) and (x2,y2) to the current plot

arrows(x1,y1,x2,y2)

adds an arrow to the current plot

for a description of optional arguments, type help(segments)

text(x,y,labels)

adds text to the current plot

the coordinates can be given by two arguments (x and y) or by a single argument x which is a univariate time series, a complex vector, a matrix with 2 columns, or a list containing components named x and y

mtext("string",side= )

adds text in the margins of the current plot

side specifies the side on which the text is to be placed

1. bottom
2. left (default)
3. top
4. right

other options are available for this function, use help(mtext)

axis

adds an axis to the current plot

box

surrounds the current plot with a box

Further Reading