Cannot create PDF by ggplot2 within if-statements - r

Question

Consider a minimal example: generating an empty plot with ggplot2 and put it into a PDF file. Typically people would do
pdf()
ggplot()
dev.off()
and it works as expected. However, when you wrap these statements into an if-statement, the resulting PDF file becomes corrupted.
if (TRUE) {
pdf()
ggplot()
dev.off()
}
This issue has been reproduced on both Windows 10 and macOS Mojave. I'm using the latest version of R
$ R --version
R version 3.6.0 (2019-04-26) -- "Planting of a Tree"
Copyright (C) 2019 The R Foundation for Statistical Computing
Platform: x86_64-apple-darwin18.6.0 (64-bit)
R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under the terms of the
GNU General Public License versions 2 or 3.
For more information about these matters see
https://www.gnu.org/licenses/.

Answer 1

To save a ggplot object using pdf or jpg functions, one has to explicitly print the ggplot.
if (TRUE) {
pdf()
print(ggplot())
dev.off()
}
This is stated in R-FAQ 7.22 Why do lattice/trellis graphics not work?
The most likely reason is that you forgot to tell R to display the graph. Lattice functions
such as xyplot() create a graph object, but do not display it (the
same is true of ggplot2 graphics, and Trellis graphics in S-PLUS). The
print() method for the graph object produces the actual display. When
you use these functions interactively at the command line, the result
is automatically printed, but in source() or inside your own functions
you will need an explicit print() statement.
So, it would not save if one simply source a script even in the absence of a conditional statement or loop (source with echo = TRUE would save the plot).
I personally prefer to use the ggsave function since it seems more flexible.
if (TRUE) {
ggplot()
ggave(filename = "plot.pdf")
}