Approximate time: 20 minutes

Learning Objectives

Consistent formatting using custom functions

When publishing, it is helpful to ensure all plots have similar formatting. To do this we can create a custom function with our preferences for the theme. Remember the structure of a function is:

name_of_function <- function(arguments) {
    statements or code that does something
}

Now, let’s suppose we always wanted our theme to include the following:

theme_bw() +
theme(axis.title=element_text(size=rel(1.5))) +
theme(plot.title=element_text(size=rel(1.5), hjust=0.5))

You can also combine multiple arguments within the same theme() function:

theme_bw() +
theme(axis.title=element_text(size=rel(1.5)), plot.title=element_text(size=rel(1.5), hjust=0.5))

If there is nothing that we want to change when we run this, then we do not need to specify any arguments. Creating the function is simple; we can just put the code inside the {}:

personal_theme <- function(){
  theme_bw() +
  theme(axis.title=element_text(size=rel(1.5))) +
  theme(plot.title=element_text(size=rel(1.5), hjust=0.5))
}

Now to run our personal theme with any plot, we can use this function in place of the lines of theme() code:

ggplot(new_metadata) +
  geom_point(aes(x=age_in_days, y=samplemeans, color=genotype, shape=celltype), size=rel(3.0)) +
  xlab("Age (days)") +
  ylab("Mean expression") +
  ggtitle("Expression with Age") +
  personal_theme()

This lesson has been developed by members of the teaching team at the Harvard Chan Bioinformatics Core (HBC). These are open access materials distributed under the terms of the Creative Commons Attribution license (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.