Can't print to pdf ggplot charts [duplicate]

Question

Possible Duplicate:
Generate multiple graphics from within an R function

Very strange thing happening to me: the following code fails to print to pdf device:

outnames <- c("1.pdf", "2.pdf") for (n in outnames){     pdf(n)     qplot(1:10)     dev.off() } 

won't print anything to pdf, even though a pdf file is generated. However,

pdf(outnames[2]) qplot(1:10) dev.off() 

will work perfectly well. Any idea why? Reproduced in R 2.11.1.

Answer 1

Gappy, that smells like the FAQ 7.22 -- so please try print(qplot(1:10)).

Answer 2

@Dirk explains why this is happening (auto printing turned off), but an alternative to opening the device, generating the plot on the device, closing the device is ggsave(). For example:

p1 <- qplot(1:10) ggsave("p1.pdf", plot = p1) 

or via a loop:

outnames <- c("1.pdf", "2.pdf") for (n in outnames){     p2 <- qplot(1:10)     ggsave(n, plot = p2) } 

At the end of that we have all the generated plots we asked for.

> list.files(pattern = ".pdf$") [1] "1.pdf"                  "2.pdf"                  [3] "p1.pdf"