R help - Nov 2002 - R bug? (if-else problem in main program)

Hi everybody, 

I've found a very interesting problem in R: the if-else statement
doesn't
work in a main program. Sounds crazy, but true. 

I tried this very easy example, and I got syntax error at the "else"
line.

Example:
 -------
a <- 1 

if ( a == 1 )
 print("yes")
else
 print("no")
 -------- 

I tried on Windows and on Linux, but none of them works.
(Detailed version info at the end of the mail.) 

Temporally you could fix it in two way: 

1. Put it in 1 line:
if ( a == 1) print("yes") else print("no")
will work. 

2. Put it in a function. 

If you have any idea for better resolve of this problem,
please send me an email, I'm not subscribed to the list. 

Thanks,
Anita 

Version info: 

1. Windows:
platform i386-pc-mingw32
arch     i386
os       mingw32
system   i386, mingw32
status
major    1
minor    5.0
year     2002
month    04
day      29
language R 

2. Linux:
platform i686-pc-linux-gnu
arch     i686
os       linux-gnu
system   i686, linux-gnu
status
major    1
minor    5.1
year     2002
month    06
day      17
language R 

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> Example:
>  -------
> a <- 1
>
> if ( a == 1 )
>  print("yes")
> else
>  print("no")
>  --------
If you want to split this over several lines, you need curly braces:

a <- 1

if ( a == 1 ) {
  print ('yes')
} else {
  print ('no')
}

Cheers, Lorenz


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This is documented in many places.  See the help page for `if', or in
fuller detail, section 3.2 of the Language Manual.

The solution is to use braces

if(a == 1) {
    print("yes")
} else {
    print("no")
}

as described in ?"if".

On Tue, 5 Nov 2002, Anita Gulyasne Goldpergel wrote:
> I've found a very interesting problem in R: the if-else statement
doesn't
> work in a main program. Sounds crazy, but true.
This is not `a main program' but using R interactively at the top (prompt)
level.  It will work in a function, the only sort of `programs' that exist
in R.

The help and manuals are your friends!

[...]

-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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I found the same thing.  But if you write the same code in a function, there
is no problem. E.g.,

myfunc<-function(a)
{
  if ( a == 1 ) {
   print("yes")
  }
  else {
   print("no")
  } 
}

# Or

myfunc<-function(a)
{
  if ( a == 1 ) 
   print("yes")
  else
   print("no")
}
> myfunc(5)
[1] "no"
> myfunc(1)
[1] "yes"

Therefore, it may be a good idea to write functions for specific tasks from
programming point of view.

Hope this is also helpful.

-Fasheng

-----Original Message-----
From: Anita Gulyasne Goldpergel [mailto:anitag at latte.harvard.edu]
Sent: Wednesday, November 06, 2002 2:22 PM
To: Lorenz Gygax
Cc: r-help at stat.math.ethz.ch
Subject: [R] Re: R bug? (if-else problem in main program)


Thank you very much everybody for your answers!
Before I wrote my message, I had tried to use
brackets. So I've discovered something, what can be
useful for everyone: 

If I put the end-bracelet in different line from else,
it doesn't work: 

if ( a == 1 ) {
 print("yes")
 }
else {
 print("no")
} 

But if I put it one line, as you wrote, like } else {
it works. 

Thanks again, 

Anita 

Lorenz Gygax writes: 
>  
> 
>> Example:
>>  -------
>> a <- 1 
>>
>> if ( a == 1 )
>>  print("yes")
>> else
>>  print("no")
>>  --------
> 
> If you want to split this over several lines, you need curly braces: 
> 
> a <- 1 
> 
> if ( a == 1 ) {
>   print ('yes')
> } else {
>   print ('no')
> } 
> 
> Cheers, Lorenz 
> 
> 
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