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!