It's useful to plot many gene expression plots on a pdf. Each page has 3x3 or 4x4 plots.

Plot_muli-plots_on_multi-page.R

# Thanks for the suggestion from Joseph Elsherbini.

library(tidyverse)
library(ggforce)

n_pages(p) # use this to get the number of pages to print
# then run a for loop to loop over pages

pdf("test.pdf")
for (i in 1:5) {
  p <- ggplot(diamonds) +
    geom_point(aes(carat, price), alpha = 0.1) +
    facet_wrap_paginate(~ cut:clarity, ncol = 3, nrow = 3, page = i)
  print(p)
}
dev.off()