Page titles for multi-page PDF using marrangeGrob and ggsave in R

Question

I am using marrangeGrob and ggsave to export a series of graphs. When I output the sample code below, it gives page numbers (e.g., 1 of 6, 2 of 6, ...) at the top of the page. I know this can easily be removed with top = NULL. But I would like to change the title for each page either from the list of plot objects (which are named) or from a character vector (e.g., plot_names below).

I know I can use other functions like textGrob along with gpar to change the title, font, size of font, etc. (e.g., changing title in multiplot ggplot2 using grid.arrange). But I have not found a straightforward way to change the title on each page.

Sample Data

library(ggplot2)
library(gridExtra)

# Create some plots
p1 <- qplot(mpg, wt, data = mtcars, colour = cyl)
p2 <- qplot(mpg, data = mtcars) + ggtitle("title")
p3 <- qplot(mpg, data = mtcars, geom = "dotplot")
plots <- list(p1, p2, p3)
plot_names <- c("A_Plot_1", "A_Plot_2", "B_Plot_1")
names(plots) <- plot_names


# Combine into a list, and change where page numbers will appear
Export <- gridExtra::marrangeGrob(plots, nrow = 1, ncol = 1)

# Export to a pdf file
ggsave(filename = "multipage.plots.pdf", Export, scale = 1.5)

Also, notice that these are not necessarily just sequential plots (e.g., A_Plot, B_Plot, etc.).

Expected Output

Here is what I would like for the PDFs to look like.

Answer 1

You can change the top parameter to something you want. The default value is

top = quote(paste("page", g, "of", npages))

So you can pass a quoted expression that will be evaulated for each plot where g is the current plot index and npages is the total number of plots. So in your case, you can extract the values from your vector

Export <- gridExtra::marrangeGrob(plots, nrow = 1, ncol = 1,
                                  top=quote(names(plots)[g]))