10 Utilities – R Graphics with ggplot2

10.1 The {patchwork} Package

While ggplot2 is excellent for creating individual visualisations, we often need to combine multiple independent plots into a single composite graphic. The {patchwork} package is designed to make this process incredibly simple by treating ggplot objects as mathematical elements that can be added together.

The power of {patchwork} lies in its operator-based syntax:

| or + : Places plots side-by-side.
/ : Stacks plots vertically.
() : Groups plots together to create complex, nested layouts.

Find out more about {patchwork} here.

# Create two plots
act_bl <- act_full |>
  filter(VISITNUM == 40)

base_info <- ggplot(data = act_bl, aes(y = ACTTOT)) +
  theme(legend.position = "bottom")

plot1 <- base_info +
  geom_boxplot(aes(x = SEX, fill = ARM))  +
  labs(fill = "ARM") # Modify legend label
plot2 <- base_info +
  geom_point(aes(x = WEIGHT, colour = ARM)) +
  labs(colour = "ARM") # Modify legend label

# Arrange side by side using patchwork syntax
library(patchwork)

# The '|' operator places plots side-by-side
plot1 | plot2

# collect the axis titles
(plot1 | plot2) +
  plot_layout(axis_titles = "collect")

10.2 The {docorator} package

The {docorator} package helps create production displays from R. Specifically, {docorator} saves TFLs to output files by providing the following functionality:

Decorate: Surround displays with document-level headers, footers, and page numbers
Output: Export decorated displays to a PDF file

Find out more about {docorator} here.

# Load package
library(docorator) 

# Create figure
myplot <- ggplot(data = theoph, aes(x = TIME, y = CONC, group = SUBJID)) +
  geom_line()


# Export display   
myplot |> 
  as_docorator( 
    display_name = "myplot",
    display_loc = "my/file/path",
    header = fancyhead(
      fancyrow(left = "My Study", center = NA, right = doc_pagenum()),
      fancyrow(left = "My Population", center = NA, right = NA),
      fancyrow(left = NA, center = "My Plot", right = NA)
    ),
    footer = fancyfoot(
      fancyrow(left = doc_path(display_name, display_loc), center = NA, right = "Data as of 2025-01-01")
    ) 
  ) |> 
  render_pdf()

10.3 Additional Packages

There are many, many more ggplot2 extensions available on CRAN (most beginning “gg*”). For example, we can add marginal histograms to scatter plots with ggExtra or cowplot. There are other packages that add new geoms such as wordclouds.