Equal panel height in different facet_grid plots, ggplot2 R

Question

I want to have two facet_grid plots side by side, one with 3 rows and another with 2 using ggplot2 in R. By default grid.arrange tries to maintain the equal height of two facet_grids however, I want to have equal panel height for both plots.Particularly I want to adjust the panel height of plot with least number of rows to be equal to the panel height of the plot with maximum number of rows. I don't think it should be quite complicated. Am I missing some common idea here? Since I am newbie to R any help would be kindly appreciated Thank you!

A reproducible example is here:

library(tidyverse)
library(gridExtra)
mtcars
p1 <- ggplot(mtcars,aes(x =mpg,y = disp,fill=cyl))+
geom_point()+
facet_grid(rows=vars(gear),cols=vars(cyl),scales = "free")

p2 <- ggplot(mtcars,aes(x =mpg,y = disp,fill=cyl))+
  geom_point()+
  facet_grid(rows=vars(am),cols=vars(cyl),scales = "free")

grid.arrange(p1,p2,ncol=2)

which produces

I want to have p2 have panel height as of p1 and use the bottom empty space from p2 (right) for the legend the remaining space empty. And yes I have to maintain scale to be free.

user_5668968 · Answer

not very elegant, but you can perhaps draw an empty rectangle, combine it vertically with your p2 and then combine with p1:

library(grid)
empty_panel <- grid.rect(gp=gpar(col="white"))

p2t <- grid.arrange(p2,empty_panel,ncol=1, heights=c(0.7,0.3))
grid.arrange(p1,p2t,ncol=2)

the output looks like

If you want the extra space to be used to place, for example, your legend, an option could be to play with legend.position and plot.margin:

p2 <- ggplot(mtcars,aes(x =mpg,y = disp,fill=cyl))+
   geom_point()+
   facet_grid(rows=vars(am),cols=vars(cyl),scales = "free")+
   
   theme(plot.margin= unit(c(0, 0, 4, 0), "cm")     ,legend.position = c(0.5, -0.3))
 
 grid.arrange(p1,p2,ncol=2)

some manual adjustment is required.

the plot will loook like:

Equal panel height in different facet_grid plots, ggplot2 R

1 Answers