Is it possible to have a multi-line comments in R?

问题:

This question already has an answer here:

• Multiline Comment Workarounds? 10 answers

I found this old thread (from over a year ago), which explains how come R doesn't support a multi-line comments (like /* comment */ of PHP, for example).

I am wondering if this has been resolved in the past year, or if there are other alternatives? (For example, in notepad++ with npptor, you can mark a bunch of lines and press ctrl+q to mark them all as comments, are there similar solutions for other IDE's ?)

回答1:

You can, if you want, use standalone strings for multi-line comments — I've always thought that prettier than if (FALSE) { } blocks. The string will get evaluated and then discarded, so as long as it's not the last line in a function nothing will happen.

"This function takes a value x, and does things and returns things that
 take several lines to explain"
doEverythingOften <- function(x) {
     # Non! Comment it out! We'll just do it once for now.
     "if (x %in% 1:9) {
          doTenEverythings()
     }"
     doEverythingOnce()
     ...
     return(list(
         everythingDone = TRUE, 
         howOftenDone = 1
     ))
}

The main limitation is that when you're commenting stuff out, you've got to watch your quotation marks: if you've got one kind inside, you'll have to use the other kind for the comment; and if you've got something like "strings with 'postrophes" inside that block, then there's no way this method is a good idea. But then there's still the if (FALSE) block.

The other limitation, one that both methods have, is that you can only use such blocks in places where an expression would be syntactically valid - no commenting out parts of lists, say.

Regarding what do in which IDE: I'm a Vim user, and I find NERD Commenter an utterly excellent tool for quickly commenting or uncommenting multiple lines. Very user-friendly, very well-documented.

Lastly, at the R prompt (at least under Linux), there's the lovely Alt-Shift-# to comment the current line. Very nice to put a line 'on hold', if you're working on a one-liner and then realise you need a prep step first.

回答2:

R Studio (and Eclipse + StatET): Highlight the text and use CTRL+SHIFT+C to comment multiple lines in Windows. Or, command+SHIFT+C in OS-X.

回答3:

CTRL+SHIFT+C in Eclipse + StatET and Rstudio.

回答4:

No multi-line comments in R as of version 2.12 and unlikely to change. In most environments, you can comment blocks by highlighting and toggle-comment. In emacs, this is 'M-x ;'.

回答5:

if(FALSE) {
...
}

precludes multiple lines from being executed. However, these lines still have to be syntactically correct, i.e., can't be comments in the proper sense. Still helpful for some cases though.

回答6:

Unfortunately, there is still no multi-line commenting in R.

If your text editor supports column-mode, then use it to add a bunch of #s at once. If you use UltraEdit, Alt+c will put you in column mode.

回答7:

Put the following into your ~/.Rprofile file:

exclude <-  function(blah) {
    "excluded block"
}

Now, you can exclude blocks like follows:

stuffiwant

exclude({
    stuffidontwant
    morestuffidontwant
})