Types of Comments in R However, in R programming, there is no functionality for multi-line comments. Thus, you can only write single-line comments in R.
Commenting Multiple Lines First way: Select the multiple lines which you want to comment using the cursor and then use the key combination “control + shift + C” to comment or uncomment the selected lines.
/* */ (multiline comment) Multiline comments are used for large text descriptions of code or to comment out chunks of code while debugging applications. Comments are ignored by the compiler.
If you use RStudio, you can use the keyboard shortcut Ctrl + Shift + C ( Command + Shift + C on macOS) to comment out a line of text.
R Studio (and Eclipse + StatET): Highlight the text and use CTRL+SHIFT+C to comment multiple lines in Windows. For macOS, use command+SHIFT+C.
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.
CTRL+SHIFT+C in Eclipse + StatET and Rstudio.
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.
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 ;'.
Put the following into your ~/.Rprofile
file:
exclude <- function(blah) {
"excluded block"
}
Now, you can exclude blocks like follows:
stuffiwant
exclude({
stuffidontwant
morestuffidontwant
})
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.
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