R: Multiline Comment Workarounds?

Question

I (sort of) already know the answer to this question. But I figured it is one that gets asked so frequently on the R Users list, that one solid good answer belongs on SO. To the best of my knowledge there is no multiline comment functionality in R. So, do you have any good workarounds?

While quite a bit of work in R usually involves interactive sessions (which casts doubt on the need for multiline comments), there are times when I've had to send scripts to colleagues and classmates, much of which involves nontrivial blocks of code. And for people coming from other languages it is a fairly natural question. So.

In the past I've used quotes. Since strings support linebreaks, running an R script with

"
Here's my multiline comment.

"
a <- 10
rocknroll.lm <- lm(blah blah blah)
 ...

works fine. Do y'all have better solutions?

Answer 1

I can think of two options. The first option is to use an editor that allows to block comment and uncomment (eg. Eclipse). The second option is to use an if statement. But that will only allow you to 'comment' correct R syntax. Hence a good editor is the prefered workaround.

if(FALSE){
     #everything in this case is not executed

}

Answer 2

This does come up on the mailing list fairly regularly, see for example this recent thread on r-help. The consensus answer usually is the one shown above: that given that the language has no direct support, you have to either

• work with an editor that has region-to-comment commands, and most advanced R editors do
• use the if (FALSE) constructs suggested earlier but note that it still requires complete parsing and must hence be syntactically correct