Robert <[EMAIL PROTECTED]> writes: > Professor, > What does if ((x=2)) 2 mean? > Thanks, > Robert
it assigns 2 to x, then uses the result (i.e. whether it is non-zero) as the condition for the if() construct. So in this case, the condition is always TRUE and the result is always 2. > Peter Dalgaard <[EMAIL PROTECTED]> wrote: > Prof Brian Ripley writes: > > > Please do read the posting guide. > > The answer to your question can be found by help("<-") or help("="). > > > > The '<-' can be used anywhere, but the '=' is > > only allowed at the top level (that is, in the complete expression > > typed by the user) or as one of the subexpressions in a braced > > list of expressions. > > > > If you don't fully understand that, just use <- always. > > The text is not completely accurate though: > > > if ((x=2)) 2 > [1] 2 > > x > [1] 2 > > if (x=2) 2 > Error: syntax error in "if(x=" > > if(x<-2) 2 > [1] 2 > > if(x < -2) 2 > > > > We do allow "=" inside parentheses too, it's only in function > arguments (where it is ambiguous) and inside conditional clauses > (where users might use it incorrectly to test for equality) that we > disallow it. > > As the last example shows, we do leave people to fry in their own fat > if they use "<-" for comparisons with negative numbers, though (been > there, done that...) > > > -- > O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B > c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K > (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 > ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 > > > --------------------------------- > Yahoo! FareChase - Search multiple travel sites in one click. -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html