[R] Sweave question

[Jason Turner]

Rafael A. Irizarry wrote:

> Using Sweave in the tools library (R version 1.8.0: sorry i havent 
> upgraded), it seems i cant use if statements in R chunks that make graphs. 
> i have this:
> 
> <<fig=TRUE,echo=F>>=
> par(mfrow=c(1,1))
> if(exists("x")) 
> 	plot(x,x)
> else{
>   plot(1,1,type="n")
>   text(1,1,"data not available.\n")
> }
> @
> 
> and I get this error:
> 
> Error:  chunk 6
> Error in parse(file, n, text, prompt) : parse error
> 
> any help is appreciated.
> 

Whenever you get an error message, copy and paste it into an R session 
(interactive) and see what happens.  At least then you'll know where the 
problem is, and whether it's a Sweave problem or a problem with your R 
syntax (in this case, it's the second option. sorry).

This problem is almost, but not quite, a FAQ.

The problem is that the "if(...)" is syntactically complete after the 
first plot() command.  The "else {" appears out of nowhere, as far as 
the R interpreter is concerned, and this makes no sense.

The fixes:

1) Always do this:

if(something) {
   do something
} else {
   do something else
}

Note exactly (!) where the curly braces are, relative to the "else".

2) wrap the whole thing in curly braces.

{
    if(something)
      do somthing
    else {
      do something else
    }
}

Cheers

Jason


-- 
Indigo Industrial Controls Ltd.
http://www.indigoindustrial.co.nz
64-21-343-545
jasont at indigoindustrial.co.nz