ggplot2 title : main, axis and legend titles


The aim of this tutorial is to describe how to modify plot titles (main title, axis labels and legend titles) using R software and ggplot2 package.

The functions below can be used :

ggtitle(label) # for the main title
xlab(label) # for the x axis label
ylab(label) # for the y axis label
labs(...) # for the main title, axis labels and legend titles

The argument label is the text to be used for the main title or for the axis labels.


Related Book:


GGPlot2 Essentials for Great Data Visualization in R

Prepare the data

ToothGrowth data is used in the following examples.

# convert dose column from a numeric to a factor variable
ToothGrowth$dose <- as.factor(ToothGrowth$dose)
head(ToothGrowth)
##    len supp dose
## 1  4.2   VC  0.5
## 2 11.5   VC  0.5
## 3  7.3   VC  0.5
## 4  5.8   VC  0.5
## 5  6.4   VC  0.5
## 6 10.0   VC  0.5

Make sure that the variable dose is converted as a factor using the above R script.

Example of plot

library(ggplot2)
p <- ggplot(ToothGrowth, aes(x=dose, y=len)) + geom_boxplot()
p

ggplot2 title, axis labels, legend titles, R programming

Change the main title and axis labels

Change plot titles by using the functions ggtitle(), xlab() and ylab() :

p + ggtitle("Plot of length \n by dose") +
  xlab("Dose (mg)") + ylab("Teeth length")

ggplot2 title, axis labels, legend titles, R programming

Note that, you can use \n to split long title into multiple lines.

Change plot titles using the function labs() as follow :

p +labs(title="Plot of length \n by dose",
        x ="Dose (mg)", y = "Teeth length")

ggplot2 title, axis labels, legend titles, R programming

It is also possible to change legend titles using the function labs():

# Default plot
p <- ggplot(ToothGrowth, aes(x=dose, y=len, fill=dose))+
  geom_boxplot()
p
# Modify legend titles
p + labs(fill = "Dose (mg)")

ggplot2 title, axis labels, legend titles, R programmingggplot2 title, axis labels, legend titles, R programming

Change the appearance of the main title and axis labels

Main title and, x and y axis labels can be customized using the functions theme() and element_text() as follow :

# main title
p + theme(plot.title = element_text(family, face, colour, size))
# x axis title 
p + theme(axis.title.x = element_text(family, face, colour, size))
# y axis title
p + theme(axis.title.y = element_text(family, face, colour, size))

The arguments below can be used for the function element_text() to change the appearance of the text :


  • family : font family
  • face : font face. Possible values are “plain”, “italic”, “bold” and “bold.italic”
  • colour : text color
  • size : text size in pts
  • hjust : horizontal justification (in [0, 1])
  • vjust : vertical justification (in [0, 1])
  • lineheight : line height. In multi-line text, the lineheight argument is used to change the spacing between lines.
  • color : an alias for colour


# Default plot
p <- ggplot(ToothGrowth, aes(x=dose, y=len)) + geom_boxplot() +
  ggtitle("Plot of length \n by dose") +
  xlab("Dose (mg)") + ylab("Teeth length")
p
# Change the color, the size and the face of
# the main title, x and y axis labels
p + theme(
plot.title = element_text(color="red", size=14, face="bold.italic"),
axis.title.x = element_text(color="blue", size=14, face="bold"),
axis.title.y = element_text(color="#993333", size=14, face="bold")
)

ggplot2 title, axis labels, legend titles, R programmingggplot2 title, axis labels, legend titles, R programming

Remove x and y axis labels

It’s possible to hide the main title and axis labels using the function element_blank() as follow :

# Hide the main title and axis titles
p + theme(
  plot.title = element_blank(),
  axis.title.x = element_blank(),
  axis.title.y = element_blank())

ggplot2 title, axis labels, legend titles, R programming

Infos

This analysis has been performed using R software (ver. 3.1.2) and ggplot2 (ver. )


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