Background of grid.arrange - r

Question

I have made a plot like the one described by the code below resulting in the posted image. I can not figure out how to set the entire background to the same "grey80"-color I have used when defining the subplots. Ie. I want to color the white areas between the plots and on the sides of the legend in the same color.
Is this possible to achieve, perhaps with some fancy gridgrob-magic?
This question is similar to change the background color of grid.arrange output but I would like a solution without using the png() function, if possible
library(ggplot2)
library(gridExtra)
library(ggthemes)
library(grid)
p1 <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width,
colour = Species)) +
ggtitle('Sepal') +
geom_point() + theme_bw() +
theme(rect = element_rect(fill = 'grey80'))
p2 <- ggplot(iris, aes(x = Petal.Length, y = Petal.Width,
colour = Species)) +
ggtitle('Petal') +
geom_point() + theme_bw() +
theme(rect = element_rect(fill = 'grey80'))
grid_arrange_shared_legend <- function(...) {
plots <- list(...)
g <- ggplotGrob(plots[[1]] + theme(legend.position = "bottom"))$grobs
legend <- g[[which(sapply(g, function(x) x$name) == "guide-box")]]
lheight <- sum(legend$height)
grid.arrange(
do.call(arrangeGrob, lapply(plots, function(x)
x + theme(legend.position="none"))),
legend,
ncol = 1,
heights = unit.c(unit(1, "npc") - lheight, lheight))
}
grid_arrange_shared_legend(p1,p2)

Answer 1

upgrade comment
You can do this by adding a grey background to the graphics window and
then adding the plots on top. As your legend function uses grid.arrange this generates a newpage; so either add newpage=FALSE or change to arrangeGrob to your function.
Your example
library(ggplot2)
library(gridExtra)
library(ggthemes)
library(grid)
p1 <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width, colour = Species)) +
ggtitle('Sepal') +
geom_point() + theme_bw() +
# by adding colour=grey removes the white border of the plot and
# so removes the lines between the plots
# add panel.background = element_rect(fill = "grey80")
# if you want the plot panel grey aswell
theme(plot.background=element_rect(fill="grey80", colour="grey80"),
rect = element_rect(fill = 'grey80'))
p2 <- ggplot(iris, aes(x = Petal.Length, y = Petal.Width, colour = Species)) +
ggtitle('Petal') +
geom_point() + theme_bw() +
theme(plot.background=element_rect(fill="grey80", colour="grey80"),
rect = element_rect(fill = 'grey80'))
Tweal your function
# Change grid.arrange to arrangeGrob
grid_arrange_shared_legend <- function(...) {
plots <- list(...)
g <- ggplotGrob(plots[[1]] + theme(legend.position = "bottom"))$grobs
legend <- g[[which(sapply(g, function(x) x$name) == "guide-box")]]
lheight <- sum(legend$height)
arrangeGrob( # change here
do.call(arrangeGrob, lapply(plots, function(x)
x + theme(legend.position="none"))),
legend,
ncol = 1,
heights = unit.c(unit(1, "npc") - lheight, lheight))
}
Plot
grid.draw(grobTree(rectGrob(gp=gpar(fill="grey80", lwd=0)),
grid_arrange_shared_legend(p1,p2)))
Which gives

Answer 2

I think you could take advantage of the ggdraw() function from the cowplot package as showed here.
In your case, you would just need to add plot.background = element_rect(fill="grey80", color = NA) in the theme() of each plot p1 and p2, stitch them together with your function grid_arrange_shared_legend() and then call ggdraw() on its output:
g <- grid_arrange_shared_legend(p1,p2)
g2 <- cowplot::ggdraw(g) +
# same plot.background should be in the theme of p1 and p2 as mentioned above
theme(plot.background = element_rect(fill="grey80", color = NA))
plot(g2)