When you have a plot with just a few facets, it’s easy to fit them all on a single page. But what if you have a whole bunch of facets that you want to visualize? For example, the USArrests dataset has data from all 50 US states.
If we just use the usual facet_wrap or facet_grid from ggplot2, you end up with one massive, smooshed-together image:
library(tidyverse)
plot_1 <- USArrests |> # dataset on US arrests
rownames_to_column("State") |> # This is just so we can see the state names
ggplot(aes(x = UrbanPop, y = Murder)) +
geom_point() +
facet_wrap(~ State,
nrow = 5, ncol = 10)
plot_1
The ggforce library, among its many useful functions, includes facet_wrap_paginate and facet_grid_paginate. These work like facet_wrap and facet_grid, but take an additional page argument. Here we specify that we want 4 rows and 5 columns per page, so for 50 states there will be 2 full pages plus one page with the remaining 10 states:
library(ggforce)
plot_2 <- plot_1 +
facet_wrap_paginate(~ State,
nrow = 4, ncol = 5, page = 2)
plot_2
Note that we had to specify which page we wanted to print. We can then easily put this into a loop to generate all the necessary pages. The helpful n_pages() will count the pages needed, which we can then use in a loop. This gives us 3 separate plots.
plot_pages <- plot_2 |>
n_pages()
for (i in 1:plot_pages) {
print(
plot_1 + facet_wrap_paginate(~ State,
nrow = 4, ncol = 5, page = i)
)
}
That’s better, but for inclusion in a longer document or for sharing the plot, you may want all three pages in a single PDF. This can be accomplished by calling pdf() before the loop and dev.off() after.1
pdf('many_plots.pdf', width = 11, height = 8.5) #start building pdf
for (i in 1:plot_pages) {
print( # don't forget this
plot_1 +
facet_wrap_paginate(~State, nrow = 4, ncol = 5, page = i)
)
}
dev.off() # end building pdfThe resulting PDF is a single file with 3 pages, as we expect.
(This post was inspired by this conversation on StackOverflow.)