Extend axis limits without plotting (in order to align two plots by x-unit)

Question

I am trying to combine two ggplot objects with patchwork - two plots with different subsets of data, but the same x variable (and therefore same unit). I would

Answer 1

Here is an option with grid.arrange that does not use a blank plot, but requires a manual of adjustment of:

• plot margin
• x axis expansion
• number of decimal places in y axis labels

library(ggplot2)
library(dplyr)
library(gridExtra)

p1 <- 
  ggplot(mtcars, aes(mpg)) + 
  geom_density(trim = TRUE) +
  scale_x_continuous(limits = c(10,35), breaks=seq(10,35,5), expand = expand_scale(add=c(0,0))) 

p2 <- 
  ggplot(filter(mtcars, mpg < 20), aes(mpg)) + 
  geom_histogram(binwidth = 1, boundary = 1) +
  scale_x_continuous(limits = c(10,20), breaks=seq(10,20,5), expand = expand_scale(add=c(0,0))) +
  scale_y_continuous(labels = scales::number_format(accuracy = 0.01)) +
  theme(plot.margin = unit(c(0,1,0,0), "cm"))

grid.arrange(p1, p2,
  layout_matrix = rbind(c(1, 1), c(2, NA))
)

Should make this plot: