I wanted to use "help in R" in order to see some information about some commands such as "for", "if", "while", "repeat" etc. But there is no information in "R help" regarding such commands. I would like to know why?
I use "R help" for the above commands like below:
?for
?while
?if
?repeat
R requires that keywords are used in syntactically valid form. The way R works, it expects that if for instance is followed by an expression in parentheses, and a body. ?if is not valid R syntax.
Conversely, ? is an operator that expects an identifier after it.
To make it valid, you should quote the if identifier in backticks. That way, R parses the expression as ? followed by an identifier, rather than ? followed by an incomplete if expression:
?`if`
Backtick-quoting is R’s way of saying: “hey, that thing between backticks is a valid identifier, even if it totally doesn’t look like one”. You could (but generally shouldn’t!) totally use it to use wonky variable names:
`name with spaces` = 2
message(`name with spaces` + 5)
# 7
This feature is more useful when applied to column names of externally imported data (which sometimes contains spaces or other invalid identifier characters), or when defining operators.