Add and customize titles

How this chapter is organized?

• Change main title and axis labels
• title colors
• The font style for titles
• Change the font size
• Use the title() function
• Customize the titles using par() function.

Read more —> Add titles to a plot in R software.

Plot titles can be specified either directly to the plotting functions during the plot creation or by using the title() function (to add titles on an existing plot).

# Add titles
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        col.main="red", col.lab="blue", col.sub="black")

# Increase the size of titles
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        cex.main=2, cex.lab=1.7, cex.sub=1.2)

Read more —> Add titles to a plot in R software.

Add legends

How this chapter is organized?

• R legend function
• Title, text font and background color of the legend box
• Border of the legend box
• Specify legend position by keywords

Read more —> Add legends to plots

The legend() function can be used. A simplified format is :

legend(x, y=NULL, legend, col)

# Generate some data
x<-1:10; y1=x*x; y2=2*y1
# First line plot
plot(x, y1, type="b", pch=19, col="red", xlab="x", ylab="y")
# Add a second line
lines(x, y2, pch=18, col="blue", type="b", lty=2)
# Add legends
legend("topleft", legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8)

Read more —> Add legends to plots

Add texts

How this chapter is organized?

• Add texts within the graph
• Add text in the margins of the graph
• Add mathematical annotation to a plot

Read more —> Add text to a plot

To add a text to a plot in R, the text() function [to draw a text inside the plotting area] and mtext()[to put a text in one of the four margins of the plot] function can be used.

A simplified format for text() is :

text(x, y, labels)

plot(cars[1:10,], pch=19)
text(cars[1:10,],  row.names(cars[1:10,]), 
     cex=0.65, pos=1,col="red") 

Read more —> Add text to a plot

Add straight lines

How this chapter is organized?

• Add a vertical line
• Add an horizontal line
• Add regression line

Read more —> abline R function : An easy way to add straight lines to a plot using R software

The R function abline() can be used to add straight lines (vertical, horizontal or regression lines) to a graph.

A simplified format is :

abline(a=NULL, b=NULL, h=NULL, v=NULL, ...)

# Add horizontal and vertical lines
#++++++++++++++++++++++++++++++++++
plot(cars, pch=19)
abline(v=15, col="blue") # Add vertical line
# Add horizontal line, change line color, size and type
abline(h=60, col="red", lty=2, lwd=3)

# Fit regression line
#++++++++++++++++++++++++++++++++++
require(stats)
reg<-lm(dist ~ speed, data = cars)
coeff=coefficients(reg)
# equation of the regression line : 
eq = paste0("y = ", round(coeff[2],1), "*x ", round(coeff[1],1))
plot(cars, main=eq, pch=18)
abline(reg, col="blue", lwd=2)

Read more —> abline R function : An easy way to add straight lines to a plot using R software

Add an axis to a plot

axis() function can be used.

A simplified format is :

axis(side, at=NULL, labels=TRUE)

x<-1:4; y=x*x
plot(x, y, pch=18, col="red", type="b",
     frame=FALSE, xaxt="n") # Remove x axis
axis(1, 1:4, LETTERS[1:4], col.axis="blue")
axis(3, col = "darkgreen", lty = 2, lwd = 0.5)
axis(4, col = "violet", col.axis = "dark violet", lwd = 2)

Read more —> Add an axis to a plot with R software.

Change axis scale : minimum, maximum and log scale

xlim and ylim arguments can be used to change the limits for x and y axis. Format : xlim = c(min, max); ylim = c(min, max).

log transformation can be performed using the parameters : log=“x”, log=“y” or log=“xy”.

x<-1:10; y=x*x
plot(x, y) # Simple graph
plot(x, y, xlim=c(1,15), ylim=c(1,150))# Enlarge the scale
plot(x, y, log="y")# Log scale

Read more —> Axis scale in R software : minimum, maximum and log scale.

Customize tick mark labels

• Color, font style and font size of tick mark labels :
• Orientation of tick mark labels
• Hide tick marks
• Change the string rotation of tick mark labels
• Use the par() function

x<-1:10; y<-x*x
# Simple graph
plot(x, y)
# Custom plot : blue text, italic-bold, magnification
plot(x,y, col.axis="blue", font.axis=4, cex.axis=1.5)

Read more —> Customize tick mark labels.

Change plotting symbols

The following points symbols can be used in R :

Point symbols can be changed using the argument pch.

x<-c(2.2, 3, 3.8, 4.5, 7, 8.5, 6.7, 5.5)
y<-c(4, 5.5, 4.5, 9, 11, 15.2, 13.3, 10.5)
# Change plotting symbol using pch
plot(x, y, pch = 19, col="blue")
plot(x, y, pch = 18, col="red")
plot(x, y, pch = 24, cex=2, col="blue", bg="red", lwd=2)

Read more —> R plot pch symbols : The different point shapes available in R.

Change line types

The following line types are available in R :

Line types can be changed using the graphical parameter lty.

x=1:10; y=x*x
plot(x, y, type="l") # Solid line (by default)
plot(x, y, type="l", lty="dashed")# Use dashed line type
plot(x, y, type="l", lty="dashed", lwd=3)# Change line width

Read more —> Line types in R : lty.

Change colors

• Built-in color names in R
• Specifying colors by hexadecimal code
• Using RColorBrewer palettes
• Use Wes Anderson color palettes
• Create a vector of n contiguous colors

Colors can be specified by names (e.g col=red) or with hexadecimal code (e.gcol = “#FFCC00”).

# use color names
barplot(c(2,5), col=c("blue", "red"))
# use hexadecimal color code
barplot(c(2,5), col=c("#009999", "#0000FF"))

Hexadecimal color charts :

(Source: http://www.visibone.com)

RColorBrewer package can also be used to create a nice looking color palettes. Read our article : Colors in R.

Read more —> Colors in R.

Related articles

Click on the following articles to read more.

Plotting symbols in R

Different plotting symbols are available in R. The graphical argument used to specify point shapes is pch.

Line types in R

The argument lty can be used to specify the line type. To change line width, the argument lwd can be used.

Colors in R

Colors can be specified either by name (e.g col = “red”) or as a hexadecimal code (such as col = “#FFCC00”). You can also use other color systems such as ones taken from the RColorBrewer package.

Add titles to a plot

Plot titles can be specified either directly to the plotting functions during the plot creation or by using the title() function (to add titles on an existing plot).

Add legends to plots

To add legends to plots in R, the R legend() function can be used.

Add texts to a plot

To add a text to a plot in R, the text() and mtext() R functions can be used.

Add straight lines

The R function abline() can be used to add vertical, horizontal or regression lines to a graph.

Add an axis to a plot

axis() function can be used to add a secondary axis to a plot.

Change axis scale in R

The goal of this article is to show you how to set x and y axis limites by specifying the minimum and the maximum values of each axis. We’ll also see how to set the log scale.

Infos

This analysis has been performed using R statistical software (ver. 3.2.4).

R legend function

To add legends to plots in R, the R legend() function can be used. A simplified format of the function is :

legend(x, y=NULL, legend, fill, col, bg)

Example :

# Generate some data
x<-1:10; y1=x*x; y2=2*y1

plot(x, y1, type="b", pch=19, col="red", xlab="x", ylab="y")
# Add a line
lines(x, y2, pch=18, col="blue", type="b", lty=2)
# Add a legend
legend(1, 95, legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8)

To avoid repeating the above R code, we can create a custom plot function as follow :

makePlot<-function(){
  x<-1:10; y1=x*x; y2=2*y1
  plot(x, y1, type="b", pch=19, col="red", xlab="x", ylab="y")
  lines(x, y2, pch=18, col="blue", type="b", lty=2)
}

Title, text font and background color of the legend box

The arguments below can be used :

• title: The title of the legend
• text.font: an integer specifying the font style of the legend text; possible values are :
  • 1: normal
  • 2: bold
  • 3: italic
  • 4: bold and italic
• bg: background color of the legend box

makePlot()
# Add a legend to the plot
legend(1, 95, legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8,
       title="Line types", text.font=4, bg='lightblue')

Border of the legend box

The arguments box.lty, box.lwd and box.col can be used to modify the line type, width and color for the legend box border, respectively.

# Remove legend border using box.lty = 0
makePlot()
legend(1, 95, legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8,
       box.lty=0)

# Change the border
makePlot()
legend(1, 95, legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8,
       box.lty=2, box.lwd=2, box.col="green")

Specify legend position by keywords

The position of the legend can be specified also using the following keywords : "bottomright", "bottom", "bottomleft", "left", "topleft", "top", "topright", "right" and "center".

The effect of using each of these keywords are shown in the figure below :

#  Example 1: line plot
makePlot()
legend("topleft", legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8)

attach(mtcars)
boxplot(mpg~cyl, 
        xlab="Cylinders", ylab="Miles/(US) gallon", 
        col=topo.colors(3))
   
legend("bottomleft", inset=.02, title="Number of Cylinders",
   c("4","6","8"), fill=topo.colors(3), horiz=TRUE, cex=0.8)

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

Add a vertical line

The simplified format is :

abline(v = y)

It draws a vertical line on the current plot at the specified ‘y’ coordinates.

# first example : Add one line
plot(cars)
abline(v=15, col="blue")

# second example : add 2 lines 
# change line colors, sizes and types
plot(cars)
abline(v=c(15,20), col=c("blue", "red"), lty=c(1,2), lwd=c(1, 3))

# third example
set.seed(1234); mydata<-rnorm(200)
hist(mydata, col="lightblue")
abline(v = mean(mydata), col="red", lwd=3, lty=2)

Note that, line types (lty) and line width (lwd) are explained here.

Add an horizontal line

The simplified format is :

abline(h = x)

It draws an horizontal line on the current plot at the specified ‘x’ coordinates.

plot(cars)
abline(h=40, col="blue")

Add regression line

lm() function is used to fit linear models.

par(mgp=c(2,1,0), mar=c(3,3,1,1))
# Fit regression line
require(stats)
reg<-lm(dist ~ speed, data = cars)
coeff=coefficients(reg)
# equation of the line : 
eq = paste0("y = ", round(coeff[2],1), "*x ", round(coeff[1],1))
# plot
plot(cars, main=eq)
abline(reg, col="blue")

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

Built-in color names in R

We will use the following custom R function to generate a plot of color names available in R :

# Generate a plot of color names which R knows about.
#++++++++++++++++++++++++++++++++++++++++++++
# cl : a vector of colors to plots
# bg: background of the plot
# rot: text rotation angle

#usage=showCols(bg="gray33")
showCols <- function(cl=colors(), bg = "grey",
                     cex = 0.75, rot = 30) {
    m <- ceiling(sqrt(n <-length(cl)))
    length(cl) <- m*m; cm <- matrix(cl, m)
    require("grid")
    grid.newpage(); vp <- viewport(w = .92, h = .92)
    grid.rect(gp=gpar(fill=bg))
    grid.text(cm, x = col(cm)/m, y = rev(row(cm))/m, rot = rot,
              vp=vp, gp=gpar(cex = cex, col = cm))
  }

The names of the first sixty colors are shown in the following chart :

# The first sixty color names
showCols(bg="gray20",cl=colors()[1:60], rot=30, cex=0.9)

# Barplot using color names
barplot(c(2,5), col=c("chartreuse", "blue4"))

showCols(cl= colors(), bg="gray33", rot=30, cex=0.75)

Specifying colors by hexadecimal code

Colors can be specified using hexadecimal color code, such as “#FFC00”

(Source: http://www.visibone.com)

# Barplot using hexadecimal color code
barplot(c(2,5), col=c("#009999", "#0000FF"))

Using RColorBrewer palettes

You have to install the RColorBrewer package as follow :

install.packages("RColorBrewer")

RColorBrewer package create a nice looking color palettes.

The color palettes associated to RColorBrewer package can be drawn using display.brewer.all() R function as follow :

library("RColorBrewer")
display.brewer.all()

You can also view a single RColorBrewer palette by specifying its name as follow :

# View a single RColorBrewer palette by specifying its name
display.brewer.pal(n = 8, name = 'RdBu')

# Hexadecimal color specification 
brewer.pal(n = 8, name = "RdBu")

## [1] "#B2182B" "#D6604D" "#F4A582" "#FDDBC7" "#D1E5F0" "#92C5DE" "#4393C3" "#2166AC"

# Barplot using RColorBrewer
barplot(c(2,5,7), col=brewer.pal(n = 3, name = "RdBu"))

Use Wes Anderson color palettes

This color palettes can be installed and loaded as follow :

# Install
install.packages("wesanderson")

# Load
library(wesanderson)

The available color palettes are :

Use the palettes as follow :

# simple barplot
barplot(c(2,5,7), col=wes.palette(n=3, name="GrandBudapest"))

library(ggplot2)
ggplot(iris, aes(Sepal.Length, Sepal.Width, color = Species)) + 
  geom_point(size = 2) + 
  scale_color_manual(values = wes.palette(n=3, name="GrandBudapest"))

Create a vector of n contiguous colors

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

# Use rainbow colors
barplot(1:5, col=rainbow(5))
# Use heat.colors
barplot(1:5, col=heat.colors(5))

# Use terrain.colors
barplot(1:5, col=terrain.colors(5))
# Use topo.colors
barplot(1:5, col=topo.colors(5))
# Use cm.colors
barplot(1:5, col=cm.colors(5))

Infos

This analysis has been performed using R (ver. 3.1.0).

Change main title and axis labels

The following arguments can be used :

# Simple graph
barplot(c(2,5))
# Add titles
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title")

title colors

The following parameters can be used to change the colors :

• col.main: color the main title
• col.lab: color of the axis titles (x and y axis)
• col.sub: color of the sub-title

barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        col.main="red", col.lab="blue", col.sub="black")

Note that, the different colors available in R software are described here.

The font style for the text of the titles

The graphical parameters to use for customizing the font of the titles are :

• font.main: font style for the main title
• font.lab: font style for the axis titles
• font.sub: font style for the sub-title

The value of these arguments should be an integer.

Use the R code below to create a plot title with bold and italic font style.

# Titles in bold and italic
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        font.main=4, font.lab=4, font.sub=4)

Change the font size

font size can be modified using the graphical parameter : cex. The default value is 1. If cex value is inferior to 1, then the text size is decreased. Conversely, any value of cex greater than 1 can increase the font size.

The following arguments can be used to change the font size :

• cex.main : text size for main title
• cex.lab : text size for axis title
• cex.sub : text size of the sub-title

An example is shown below :

# Increase the size
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        cex.main=2, cex.lab=1.7, cex.sub=1.2)

Use the title() function

title() can be also used to add titles to a graph.

A simplified format is :

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

Example of usage

x<-1:10; y<-x*x
plot(x,y, main = "", xlab="", ylab="",
     col.axis="blue") 
title(main = "Main title", sub = "Sub-title",
      xlab = "X axis", ylab = "Y axis",
      cex.main = 2,   font.main= 4, col.main= "red",
      cex.sub = 0.75, font.sub = 3, col.sub = "green",
      col.lab ="darkblue"
      )

Customize the titles using par() function

Note that, the R par() function can be used to change the color, font style and size for the graph titles. The modifications done by the par() function are called ‘permanent modification’ because they are applied to all the plots generated under the current R session.

Read more on par() by clicking here.

par(
  # Change the colors
  col.main="red", col.lab="blue", col.sub="black",
  # Titles in italic and bold
  font.main=4, font.lab=4, font.sub=4,
  # Change font size
  cex.main=2, cex.lab=1.7, cex.sub=1.2
  )

barplot(c(2,5), main="TMain title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub title")

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

Arguments

The following plot parameters can be used :

• xlim: the limit of x axis; format : xlim = c(min, max)
• ylim: the limit of y axis; format: ylim = c(min, max)

Transformation to log scale:

• log = “x”
• log = “y”
• log = “xy”*

log : character indicating if x or y or both coordinates should be plotted in log scale.

Examples

x<-1:10; y=x*x

# Simple graph
plot(x, y)

# Enlarge the scale
plot(x, y, xlim=c(1,15), ylim=c(1,150))

# Log scale
plot(x, y, log="y")

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

Color, font style and font size of tick mark labels :

For this end, the following argument can be used :

• col.axis : the color to be used for tick mark labels
• font.axis : an integer specifying the font style; possible values are :
  • 1: normal text
  • 2: bold
  • 3: italic
  • 4: bold and italic
  • 5 : symbol font
• cex.axis : the size for tick mark labels; default value is 1.

x<-1:10; y<-x*x
# Simple graph
plot(x, y)
# Custom plot : blue text, italic-bold, magnification
plot(x,y, col.axis="blue", font.axis=4, cex.axis=1.5)

Orientation of tick mark labels

To change the style of the tick mark labels, las argument can be used. The possible values are :

• 0: the labels are parallel to the axis (default)
• 1: always horizontal
• 2 : always perpendicular to the axis
• 3 : always vertical

plot(x, y, las=0) # parallel
plot(x, y, las=1) # horizontal
plot(x, y, las=2) # perpendicular

Hide tick marks

To hide or to show tick mark labels, the following graphical parameters can be used :

• xaxt : a character specifying the x axis type; possible values are either “s” (for showing the axis) or “n” ( for hiding the axis)
• yaxt : a character specifying the y axis type; possible values are either “s” (for showing the axis) or “n” ( for hiding the axis)

These two arguments are very useful to take the control of the rotation angle for tick mark labels. Changing the rotation angle is not something easy in R but we’ll see how to do it in the next section.

# Hide x and y axis
plot(x, y, xaxt="n", yaxt="n")

Change the string rotation of tick mark labels

The following steps can be used :

1. Hide x and y axis
2. Add tick marks using the axis() R function
3. Add tick mark labels using the text() function

The argument srt can be used to modify the text rotation in degrees.

# Suppress the axis
plot(x, y, xaxt="n", yaxt="n")

# Changing x axis
xtick<-seq(0, 10, by=5)
axis(side=1, at=xtick, labels = FALSE)
text(x=xtick,  par("usr")[3], 
     labels = xtick, srt = 45, pos = 1, xpd = TRUE)

# Changing y axis
ytick<-seq(0, 100, by=50)
axis(side=2, at=ytick, labels = FALSE)
text(par("usr")[1], ytick,  
     labels = ytick, srt = 45, pos = 2, xpd = TRUE)

Use the par() function

The par() function can be used to permanently apply the changes to all of the graphs that will be created in the current session.

par(col.axis="blue", font.axis=4, cex.axis=1.5)
plot(x,y)

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

Add texts within the graph

The text() function can be used to draw text inside the plotting area. A simplified format of the function is :

text(x, y, labels)

An example is shown below :

d<-head(mtcars)

plot(d[,&#39;wt&#39;], d[,&#39;mpg&#39;], 
     main="Milage vs. Car Weight\n~~~~~~~~~~~~~~~~~~~",
      xlab="Weight", ylab="Miles/(US) gallon",
      pch=19, col="darkgreen")

text(d[,&#39;wt&#39;], d[,&#39;mpg&#39;],  row.names(d),
     cex=0.65, pos=3,col="red") 

Add text in the margins of the graph

The mtext() R function can be used to put a text in one of the four margins of the plot. A simplified format of the function is :

mtext(text, side=3)

An example is shown below :

plot(1:10, 1:10, 
     main="mtext(...) examples\n~~~~~~~~~~~")
mtext("Magic function", side=3)

Add mathematical annotation to a plot

plot(1:10, 1:10, 
     main="text(...) examples\n~~~~~~~~~~~")
text(4, 9, expression(hat(beta) == (X^t * X)^{-1} * X^t * y))
text(7, 4, expression(bar(x) == sum(frac(x[i], n), i==1, n)))

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

Plotting symbols

The different points symbols commonly used in R are shown in the figure below :

The function used to generate this figure is provided at the end of this document

Point can be omitted from the plot using pch = NA.

Examples

x<-c(2.2, 3, 3.8, 4.5, 7, 8.5, 6.7, 5.5)
y<-c(4, 5.5, 4.5, 9, 11, 15.2, 13.3, 10.5)
# Plot points
plot(x, y)

# Change plotting symbol
# Use solid circle
plot(x, y, pch = 19)

By default pch=1

The following arguments can be used to change the color and the size of the points :

• col : color (code or name) to use for the points
• bg : the background (or fill) color for the open plot symbols. It can be used only when pch = 21:25.
• cex : the size of pch symbols
• lwd : the line width for the plotting symbols

# Change color
plot(x, y, pch=19, col="darkgreen", cex=1.5)

# Color can be a vector
plot(x, y, pch=19, col=c("green", "red"))

# change border, background color and line width
plot(x, y, pch = 24, cex=2, col="blue", bg="red", lwd=2)

Note that, only pch from 21 to 25 can be filled using the argument bg=

Other characters can be used to specify pch including “+”, “*“,”-“,”.“,”#, “%”, “o”

set.seed(1234)
plot(x=rnorm(100), y=rnorm(100), pch="+")

R script to generate a plot of point shapes in R

Use the following R function to display a graph of the plotting symbols :

#++++++++++++++++++++++++++++++++++++++++++++
#generate a plot of point shapes which R knows about.
#++++++++++++++++++++++++++++++++++++++++++++
generateRPointShapes<-function(){
  oldPar<-par()
  par(font=2, mar=c(0.5,0,0,0))
  y=rev(c(rep(1,6),rep(2,5), rep(3,5), rep(4,5), rep(5,5)))
  x=c(rep(1:5,5),6)
  plot(x, y, pch = 0:25, cex=1.5, ylim=c(1,5.5), xlim=c(1,6.5), 
       axes=FALSE, xlab="", ylab="", bg="blue")
  text(x, y, labels=0:25, pos=3)
  par(mar=oldPar$mar,font=oldPar$font )
}
generateRPointShapes()

Infos

This analysis has been performed using R (ver. 3.1.0).