I'm trying to save a ggplot within a function using graphics devices. But I found the code produces empty graphs. Below is a very very simple example.
library(ggplot2)
ff <- function(){
jpeg("a.jpg")
qplot(1:20, 1:20)
dev.off()
}
ff()
If I only run the content of the function, everything is fine. I know that using ggsave() will do the thing that I want, but I am just wondering why jpeg() plus dev.off() doesn't work. I tried this with different versions of R, and the problem persists.
You should use ggsave
instead of the jpeg(); print(p); dev.off()
sequence. ggsave
is a wrapper that does exactly what you intend to do with your function, except that it offers more options and versatility. You can specify the type of output explicitly, e.g. jpg or pdf, or it will guess from your filename extension.
So your code might become something like:
p <- qplot(1:20, 1:20)
ggsave(filename="a.jpg", plot=p)
See ?ggsave
for more details
The reason why the original behaviour in your code doesn't worked is indeed a frequently asked question (on stackoverlflow as well as the R FAQs on CRAN). You need to insert a print
statement to print the plot. In the interactive console, the print is silently execututed in the background.
These plots have to be printed:
ff <- function(){
jpeg("a.jpg")
p <- qplot(1:20, 1:20)
print(p)
dev.off()
}
ff()
This is a very common mistake.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With