How to Center Plot Title in ggplot2 with R

The easiest way to center a title using ggplot2 is to modify the plot.title component of the theme using element_text(hjust=0.5). For example,

library(ggplot2)
ggplot(data=mtcars, aes(x=mpg, y=wt)) + geom_point() + 
     ggtitle("Automobile Weight vs Miles per Gallon") +
     theme(plot.title=element_text(hjust=0.5))

This tutorial will go through how to adjust the plot title using ggplot2 with code examples.

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Example

Consider the following scatterplot of two variables from the mtcars dataset miles per gallon (mpg) and weight (wt).

library(ggplot2)

# Create scatterplot using ggplot2

ggplot(data=mtcars, aes(x=mpg, y=wt)) + geom_point() + 
     ggtitle("Automobile Weight vs Miles per Gallon")

By default, plot titles in ggplot2 are left-aligned.

Center Aligned using hjust

We can adjust the plot theme using plot.title and element_text. The function element_text specifies the display of the text component of the plot.

The hjust argument for element_text shifts the plot title text horizontally. If we set hjust to 0.5, we centre the title. Let’s look at the revised code:

library(ggplot2)
ggplot(data=mtcars, aes(x=mpg, y=wt)) + geom_point() + 
     ggtitle("Automobile Weight vs Miles per Gallon") +
     theme(plot.title=element_text(hjust=0.5))

We can see that the title is now centre-algined.

Center Aligned using hjust and vjust

We can shift the title horizontally and vertically using the hjust and vjust arguments. If we set vjust to a negative value the title moves down the plot, if we set it to a positive value the title moves up the plot. Let’s look at the revised code:

library(ggplot2)
ggplot(data=mtcars, aes(x=mpg, y=wt)) + geom_point() + 
     ggtitle("Automobile Weight vs Miles per Gallon") +
     theme(plot.title=element_text(hjust=0.5, vjust=-7))

We can see that the title has moved down and is inside the plot.

Right Aligned using hjust and vjust

We can set right-align the title by setting hjust to 1. Let’s look at the revised code:

ggplot(data=mtcars, aes(x=mpg, y=wt)) + geom_point() + 

     ggtitle("Automobile Weight vs Miles per Gallon") +

     theme(plot.title=element_text(hjust=1, vjust=-7))

We can see that the title is right-aligned and shifted down inside the plot.

Summary

Congratulations on reading to the end of this tutorial!

For further reading on R, go to the articles: 

• How to Transpose a Data Frame in R
• How to Apply a Function to Every Row of a Table in R using dplyr
• How to Remove Legend in ggplot2

Go to the online courses page on R to learn more about coding in R for data science and machine learning.

Have fun and happy researching!