plot_annotations disappear via patchwork in R

Question

I am trying to plot two patchwork objects together. The code works but plot_annotations disappear.

How can this be fixed?

Data + code:

library(tidyverse)
library(patchwork)

#Plot 1
GG1 = ggplot(iris,aes(x=Sepal.Length,y=Sepal.Width))+
  geom_point()
#Plot 2
GG2 = ggplot(iris,aes(y=Sepal.Length,x=Sepal.Width))+
  geom_point()
#Plot 3
GG3 = ggplot(iris,aes(y=Petal.Width,x=Sepal.Width))+
  geom_point()
#Plot 4
GG4 = ggplot(iris,aes(y=Petal.Length,x=Petal.Width))+
  geom_point()


combine_1 =  GG1 + GG2 +
  plot_annotation(title = 'Combine plot 1',
                  theme = theme(plot.title = element_text(hjust = 0.5)))

combine_2 =  GG3 + GG4 +
  plot_annotation(title = 'Combine plot 2',
                  theme = theme(plot.title = element_text(hjust = 0.5)))

combine_1/combine_2

Output

Answer 1

I'm afraid that your desired result could not be achieved via plot_annotation as according to the docs

... it will only have an effect on the top level plot.

But it would be a nice feature.

As a workaround you could add titles to your combined subplots as textGrobs.

Notes:

1. To make this work I had to wrap the textGrobs inside wrap_elements.
2. I also encountered some issues with setting the plot_layout that's why I had to use plot_layout(heights = c(1, 10, 11)) for the final plot.

library(ggplot2)
library(patchwork)
library(grid)
#Plot 1
GG1 = ggplot(iris,aes(x=Sepal.Length,y=Sepal.Width))+
  geom_point()
#Plot 2
GG2 = ggplot(iris,aes(y=Sepal.Length,x=Sepal.Width))+
  geom_point()

title1 <- grid::textGrob(label = "Combine Plot1")
title2 <- grid::textGrob(label = "Combine Plot2")

combine_1 =  (wrap_elements(panel = title1) / (GG1 + GG2)) + plot_layout(heights = c(1, 10))
combine_2 =  (wrap_elements(panel = title2) / (GG1 + GG2)) + plot_layout(heights = c(1, 10))

(combine_1 / combine_2) +  plot_layout(heights = c(1, 10, 11))

EDIT When answering this related question I was able to come up with an easier approach to add multiple plots which simply wraps the combined plots together by wrapping each inside patchwork::wrap_elements:

combine_1 =  (GG1 + GG2) & plot_annotation(title = "Combine Plot1") & theme(plot.title = element_text(hjust = .5))
combine_2 =  (GG1 + GG2) & plot_annotation(title = "Combine Plot2") & theme(plot.title = element_text(hjust = .5))

wrap_elements(combine_1) / wrap_elements(combine_2)