Hallo Martin I understand. Anyway, it would not do any harm to add something like
x <- 11 if(x < 0) {print("weird")} else if(x >= 0 & x <= 9) { print("too low")} else if (x > 9 & x <= 10) { print("just enough")} else { print("more than expected")} to the help page for if. Regards Petr > -----Original Message----- > From: Martin Maechler <maech...@stat.math.ethz.ch> > Sent: Wednesday, December 7, 2022 12:16 PM > To: PIKAL Petr <petr.pi...@precheza.cz> > Cc: R-help Mailing List <r-help@r-project.org> > Subject: Re: [R] if documentation > > >>>>> PIKAL Petr > >>>>> on Wed, 7 Dec 2022 07:04:38 +0000 writes: > > > Hallo all Not sure if it is appropriate place but as I am > > not involved in r-devel list I post here. > > > > > Documentation for Control (if, for, while, .) is missing > > "if else" command. Although it can be find online > > elsewhere I believe that adding it either as an example or > > as a third entry and paragraph about nested if's could be > > beneficial. > > > > > if(cond) cons.expr else if (cond) alt.expr else alt2.expr > > > Nested if expressions are better realized with "else if" > > instead of sequence of plain "else" control statements > > especially when using several of them. > > I agree. However there is no "else if" special. > > As everything that *happens* in R is a function call (John Chambers), indeed, `if` > is a function too, with an unusual syntax which may involve `else`. > > If you look more closely, `if` is a function with 3 arguments, where the last (3rd) > is optional and has a default of NULL : > > Some code towards proving the above : > > > (t1 <- if(TRUE) 1:3 ) # is identical to if(TRUE) 1:3 else NULL > f1 <- if(FALSE) 1:3 # is identical to > f2 <- if(FALSE) 1:3 else NULL > identical(f1,f2) > f3 <- if(FALSE) 1:3 else 111 > > `if`(TRUE, 1:3) > `if`(TRUE, 1:3, NULL) > > `if`(FALSE, 1:3) # returns invisibly > `if`(FALSE, 1:3, NULL) > `if`(FALSE, 1:3, 111) > > -------------- > > So, 'if(.) else' or 'if(...) else if(..) ..' > etc are > all just versions of calling the `if` function sometimes, in a nested way.
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