How to create a common title in X and Y axis in an arrange of plots using `ggdraw` and `plot_grid()` in R?

Question

I have an arrange of plots for which I would like to create a common X-axe title and a common Y-axe title. As an example:

library(ggplot2)
library(cowplot)
library(ggpubr)z
theme_set(theme_cowplot())

df <- data.frame(x = 1:12, y = (1:12)^2)
df$grp = c('Some', 'Things', 'In a legend')

p <- ggplot(df, aes(x, y, color=grp)) + geom_point()
leg <- get_legend(p)
leg <- as_ggplot(leg)
p = p + theme(legend.position = "none")

plot_grid(
  p, p, leg, 
  p, p, leg,
  ncol = 3, rel_widths=c(2,2,1)
)

After some reading, I found as an option the use of ggdraw . However, I don't know how it works well, and I don't figure out how to get what I want (one Y in the y-axis and one X in the x-axis). Below is what I tried:

• I did the same than before but I removed also X and Y-axis titles for each plot

df <- data.frame(x = 1:12, y = (1:12)^2)
df$grp = c('Some', 'Things', 'In a legend')

p <- ggplot(df, aes(x, y, color=grp)) + geom_point()
leg <- get_legend(p)
leg <- as_ggplot(leg)
p = p + theme(legend.position = "none",axis.title.x =element_blank(),axis.title.y =element_blank()) # I remove x and y titles for the plots

P <-plot_grid(
  p, p, leg, 
  p, p, leg,
  ncol = 3, rel_widths=c(2,2,1)
)
P

• Then, using ggdraw , I created an arrange of plots with one x-axis title in my desired position. However, I don't know how to get the same for the y-axe. I don't know how to increase the y-axe margin to add a label. Below is the code I tried so far:

P1 <- ggdraw(add_sub(P , "X", vpadding=grid::unit(0.8,"lines"), # With `0.8` I add some space in the X margin.
y=2, x=1, vjust=1, # With `y` and `x` I can indicate the coordinates for my desired text
angle=0) # With this I can change the orientation of the text
)
P1 

Does anyone know how to create a common x and y-axis using ggdraw or with another function?

Answer 1

I think you just need to play around with the margins before add_sub :

P <-plot_grid(
 p, p, leg, 
 p, p, leg,
 ncol = 3, rel_widths=c(2,2,1)
) + theme(plot.margin = margin(30, 30, -50, 50))

P <- add_sub(P, "x axis text", hjust = 1)
P <- add_sub(P, "y axis text", -0.05, 5, angle = 90)
ggdraw(P)