Reading PDF plots, arranging them on a grid, save

I have 3 R plots saved as pdf files (upper_left.pdf, upper_right.pdf, lower.pdf) as vector graphic and want to make a one-page pdf file and arrange them on it as follows:

What I have tried already

I have tried reading the pdf's using magick::image_read_pdf and appending them using magick::image_append. More specifically,

library(magick)

panel.ul <- image_read_pdf("upper_left.pdf")
panel.ur <- image_read_pdf("upper_right.pdf")
panel.l <- image_read_pdf("lower.pdf")

whole <- c(panel.ul, panel.ur) %>% 
    image_append() %>% 
    c(panel.l) %>% 
    image_append(stack = TRUE)

The first issue is magick::image_read_pdf imports the plot as png (if I'm right, not vector graphic though).

magick::image_append also 'works' and gives me what I want in viewer pane (in RStudio, next to Help).

I then try to save them using export::graph2pdf(whole), but it gives me a blank page.

So, if I am to use magick, there are two issues that need to be solved:

importing plots as vector graphic objects (do not know the technical term in R)
Exporting the stacked plot to a vector pdf file.

How can I solve it? thanks in advance.

You're basically done. You only need to add

plot(whole) # plot the external object generated in ImageMagick to R's plotting device
savePlot(type = "pdf") # saves the current plotting device to a pdf file.

You will find your plot in your workoing directory called "Rplot.pdf". savePlot has many options to customize your pdf output. Make sure to check ?savePlot.

To recreate your scheme from above youll need to temporarily save the upper panel as a separate pdf before you paste it to on top of the lower panel:

whole2 <- image_append(c(panel.ul, panel.ur))
plot(whole2)
savePlot("whole2.pdf", type = "pdf")

If the upper and lower panel do not look proportionate you can use the heght and width parameters of savePlot to adjust the size of the first pdf.

panel.upr <-   image_read_pdf("whole2.pdf")
final <-  image_append(c(image_append(panel.upr),panel.l), stack = TRUE)
plot(final)
savePlot("final.pdf", type = "pdf")