simple if...else causes syntax error
Thanks to everyone who took the time to point out the simple error. You would not think I have been programming in R/S for over a year. Could it be that the code works when enclosed in a function? I tested my code and it worked previously, but I was running it line by line and discovered my syntax error. Thanks again. Roger On Mon, 7 Mar 2005 08:36:50 -0800 (PST), Thomas Lumley
<tlumley at u.washington.edu> wrote:
On Mon, 7 Mar 2005, roger bos wrote:
I am trying to do the simplest thing in the world. The following works: aaa <- ifelse(aaa==5, 6, 7) But if I want to change the if...else syntax instead, it gives errors and assigns 7 to aaa. Here is the problem code:
Other people have told you how to fix this. I will point out in addition
that if...else is not different syntax for ifelse() but a very different
construct.
ifelse() is a function that operates on vectors and returns a vector that
is always the same length as the first argument. It does not change the
flow of execution: all three of the arguments are evaluated.
if(){} else {} chooses which branch of code to evaluate based on a single
logical value. The value returned by this expression could be of
completely different length and type depending on which code was
evaluated.
It might also be worth noting that the behaviour of newlines in
terminating if() {} expressions is unavoidable in an interpreter using
this syntax. When the user types
if(condition){
some.code()
}
the interpreter cannot possibly tell whether an `else' clause is coming.
Avoiding the problem would require a fairly significant change to the
language, not just to the parser, eg adding an endif (the shell script
solution), or requiring parentheses around the whole expression (the LISP
solution, and in a sense the Python solution, though there the parentheses
are invisible)
-thomas