ggreveal

ggreveal is an R package that makes it easy to present data on ggplot2 graphs incrementally. The functions in this package take a plot and break it down into a series of intermediary plots that can be shown in sequence (e.g. in different slides). Like this:

Why would you want to do that? Because it’s fun and very useful for teaching and giving talks.

Installation

install.packages("ggreveal")

Usage

Create a graph with ggplot2 as usual.

library(palmerpenguins)
library(ggplot2)
library(ggreveal)

p <-  ggplot(penguins[!is.na(penguins$sex),],
             aes(body_mass_g, bill_length_mm,
                 group=sex, color=sex)) +
      geom_point() +
      geom_smooth(method="lm", formula = 'y ~ x', linewidth=1) +
      facet_wrap(~species) +
      theme_minimal()
p

Then use one of the reveal_* functions (reveal_layers(), reveal_aes(), reveal_groups(), reveal_panels(), reveal_x()) to obtain a list of plots that show elements incrementally.

plot_list <- reveal_groups(p)
plot_list
#> [[1]]

#> 
#> [[2]]

#> 
#> [[3]]

You can also use reveal_patchwork() to incrementally reveal the individual plots in a patchwork object.

The most common use case is to show the plots in different slides of a presentation. You can work directly with the list of plots returned by the functions (useful for Quarto and R Markdown presentations), or save the plots as separate files and include them in your presentation software of choice. reveal_save() is a convenient function to save the plots in a list:

reveal_save(plot_list, "myplot.png", width = 8, height = 4)

── Saving incremental plots ──

✔ myplot_0.png
✔ myplot_1.png
✔ myplot_2_last.png

Wait, can’t ggplot2 do this already?

Yes and no. ggplot2 is composable by design, so it is straightforward to do some incremental reveal out of the box. For example, you can create the plot in steps and save the steps separately:

data("mtcars")
p1 <- ggplot(mtcars, 
            aes(mpg, wt)) +
     geom_point() 
     
p2 <- p1 + geom_smooth(method="lm", formula="y~x") 

The problem is that, as you add layers and other elements, several visual aspects of the plot — e.g. range of axes, legends — can, and will often, change. Showing how the layout changes as you add elements is useful for teaching how to make graphs in ggplot2, but it is distracting when you want to focus on the results. Keeping the layout fixed is sometimes easy (e.g. setting the limits argument for the x/y scale), but in many cases it requires tinkering with the internals of the ggplot object.