grid arrange textGrob() and ggplots. Title and subtitle gridExtra - r

Question

Basically, I want to add a title and subtitle to a grid.arrange() plot.
I have plot_list which is a list of 15 ggplots and
tg <- textGrob('Title', gp = gpar(fontsize = 13, fontface = 'bold'))
sg <- textGrob('Subtitle', gp = gpar(fontsize = 10))
But this doesn't work. I don't get any errors but tg and sg don't show up in the plot.
grid.arrange(tg, sg, grobs = plot_list, ncol = 3)
To be honest, I'm no expert in gridExtra and grid so any advice will be appreciated

Answer 1

Following changing multiple line title in multiplot ggplot2 using grid.arrange I could do what you asked for by creating two grids, first with only the plots and second with title, subtitle and the first grid. Using a synthetic plot_list:
df <- data.frame(v1 = rnorm(1000))
plot_list <- list()
for (i in 1:15) {
df[,ncol(df)+1] <- rnorm(1000)
names(df)[ncol(df)] <- paste0("V_",as.character(i))
local({
i <- i
plot_list[[i]] <<- ggplot(df) + geom_point(aes_string(x = "v1", y = paste0("V_",as.character(i))))
})
}
tg <- textGrob('Title', gp = gpar(fontsize = 13, fontface = 'bold'))
sg <- textGrob('Subtitle', gp = gpar(fontsize = 10))
margin <- unit(0.5, "line")
grided <- gridExtra::grid.arrange(grobs = plot_list, ncol = 3)
gridExtra::grid.arrange(tg, sg, grided,
heights = unit.c(grobHeight(tg) + 1.2*margin,
grobHeight(sg) + margin,
unit(1,"null")))
Hope this helps!

Answer 2

You need to combine tg, sg and your plots into a list. I would specify a layout matrix, which gives you a bit more control, and plot using grid.arrange:
First, we have tg,sg and I make a plot_list of 3 with mtcars.
library(ggplot2)
library(gridExtra)
library(grid)
tg <- textGrob('Title', gp = gpar(fontsize = 13, fontface = 'bold'))
sg <- textGrob('Subtitle', gp = gpar(fontsize = 10))
plot_list <- lapply(c("drat","wt","qsec"),function(i){
ggplot(mtcars,aes_string("mpg",i))+geom_point()
})
We combine your plots in a list:
g = c(list(tg),list(sg),plot_list)
So now tg is 1st element, sg is 2nd element and your plots are 3-5. We specify the layout:
N = length(plot_list)
laym = rbind(rep(1,N),rep(2,N),(3:(N+2)))
laym
[,1] [,2] [,3]
[1,] 1 1 1
[2,] 2 2 2
[3,] 3 4 5
This matrix will have the first one (tg), 1 takes up first row, sg 2nd row and your plots third row. If you have other kinds of arrangements or list, you can change this accordingly.
Now we plot, and specify the relative heights using heights=...
grid.arrange(grobs=g,layout_matrix=laym,heights=c(1,1,10))

Answer 3

the top argument can take any grob but it needs to know its height to be given the right space,
library(grid)
library(gridExtra)
lg <- replicate(12, ggplot2::ggplot(), simplify = FALSE)
tg <- textGrob('Title', gp = gpar(fontsize = 50, fontface = 'bold'))
sg <- textGrob('Subtitle', gp = gpar(fontsize = 10))
lt <- list(tg, sg)
heights <- do.call(unit.c, lapply(lt, function(.g) 1.5*grobHeight(.g)))
titles <- gtable::gtable_matrix('title',
grobs = matrix(lt, ncol=1),
widths = unit(1,'npc'),
heights = heights)
grobHeight.gtable <- function(g) sum(g$heights)
grid.arrange(grobs = lg, top = titles)