R help - Dec 2003 - Sweave question

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.

thanks and apologies if this not a problem in R 1.8.1
rafael

Write the if-else statement as

if(exists("x")) {
	plot(x,x)
} else{
  plot(1,1,type="n")
  text(1,1,"data not available.\n")
}

so the first two lines are not syntactically complete.

"Rafael A. Irizarry" <ririzarr at jhsph.edu> writes:
> 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.
> 
> thanks and apologies if this not a problem in R 1.8.1
> rafael
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
-- 
Douglas Bates                            bates at stat.wisc.edu
Statistics Department                    608/262-2598
University of Wisconsin - Madison        http://www.stat.wisc.edu/~bates/

This is the standard problem with if ... else: that will not work at the
command line either.  Use braces like

if(exists("x")) {
  plot(x,x)
} else {
   plot(1,1,type="n")
   text(1,1,"data not available.\n")
}

which should do the trick.

On Tue, 23 Dec 2003, 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.
>
> thanks and apologies if this not a problem in R 1.8.1
> rafael
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

On Tue, 23 Dec 2003, 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")
> }
> @
>
I think your problem is with the `else'.  The `if' part of the statement
is syntactically complete, so the parser isn't expecting an `else'.  You
need something like

  if (exists("x")){
	plot(x,x)
  } else {
	plot(1,1,type="n")
  }



	-thomas

I'm not certain, but since you are getting a parse error, I would try
curly brackets on your if statement:

    <<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")
    }
    @

HTH,

+ seth

On Tuesday 23 December 2003 09:44, 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)
This is a problem even outside of Sweave. The last line above syntactically 
completes the if statement. You need to replace it by something like 

if(exists("x")) {
 	plot(x,x)
  } else {
...
> 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.
>
> thanks and apologies if this not a problem in R 1.8.1
> rafael
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help

>>>>> "Rafael" == Rafael A Irizarry <ririzarr at
jhsph.edu>
>>>>>     on Tue, 23 Dec 2003 10:44:38 -0500 (EST) writes:
    Rafael> Using Sweave in the tools library (R version 1.8.0:
    Rafael> sorry i havent upgraded), it seems i cant use if
    Rafael> statements in R chunks that make graphs.  i have
    Rafael> this:

    Rafael> <<fig=TRUE,echo=F>>    Rafael> par(mfrow=c(1,1))
    Rafael> if(exists("x")) 
    Rafael>    plot(x,x)
    Rafael> else{
    Rafael>    plot(1,1,type="n")
    Rafael>    text(1,1,"data not available.\n")
    Rafael> }
    Rafael> @

    Rafael> and I get this error:

    Rafael> Error:  chunk 6
    Rafael> Error in parse(file, n, text, prompt) : parse error


This has nothing to do with Sweave;
it's a famous "beginner"s (;-) mistake:

?if   has the explanation :

 if> Note that it is a common mistake to forget putting braces ('{
..}')
 if> around your statements, e.g., after 'if(..)' or
'for(....)'.
 if> In particular, you should not have a newline between '}' and 
 if> 'else' to avoid a syntax error in entering a 'if ...
else'
 if> construct at the keyboard or via 'source'. For that reason, one
 if> (somewhat extreme) attitude of defensive programming uses braces
 if> always, e.g., for 'if' clauses.

Regards,
and Merry Christmas to all R-help readers!
Martin

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


-- 
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http://www.indigoindustrial.co.nz
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