How to save a grid plot in R?

Question

I have a grid plot object g.

class(g)
"gtable" "grob"   "gDesc" 

I can use grid.draw(g) to draw the plot. However, I cannot figure out a way to save the plot to a pdf file.

I tried:

ggsave(g, file="plot.png")

But apparently ggsave doesn't work on such an object.

Here is an example from the ?grid.draw help page:

grid.newpage()
## Create a graphical object, but don't draw it
l <- linesGrob()
## Draw it
grid.draw(l)

Drawing works well, but saving/printing causes the problem.

Any workaround on this? Thanks!

Answer 1

This is what MrFlick answered, but for PDFs (what you asked for in your question).

## Initiate writing to PDF file
pdf("path/to/file/PDFofG.pdf", height = 11, width = 8.5, paper = "letter")

## Create a graphical object g here
g # print it

## Stop writing to the PDF file
dev.off()

Answer 2

It may be worth adding that updated ggsave version facilites the desired export.

Packages

# Load
lapply(c("ggplot2",
         "gridExtra"), 
       require, 
       character.only = TRUE)
sessionInfo()

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] gridExtra_2.2.1 ggplot2_2.1.0  

loaded via a namespace (and not attached):
[1] colorspace_1.2-6 grid_3.1.1       gtable_0.2.0     munsell_0.4.3    plyr_1.8.3       Rcpp_0.12.6     
[7] scales_0.4.0     tools_3.1.1  

Graph preparation and export

a  <- ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = cyl))

b  <- ggplot(data = mtcars) +
  geom_line(aes(x = wt, y = vs))

# grid
gridAB  <- grid.arrange(a, b)
# Export
ggsave(filename="ab.pdf", plot=gridAB)

Class

> class(gridAB)
[1] "gtable" "gTree"  "grob"   "gDesc" 

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Preview