[R] generic handling of NA and NaN and NULL

[Liaw, Andy]

Try:

f <- function(n) {
  if(is.null(n) || is.na(n) || abs(n) < pi) {
    return(FALSE)
  } else {
    return(TRUE)
  }
}

Note that the order of the conditions inside if() matters: is.na(n) only
gets evaluated if is.null(n) is FALSE, and so on.

Andy

> -----Original Message-----
> From: Robin Hankin [mailto:r.hankin at auckland.ac.nz]
> Sent: Thursday, February 13, 2003 5:36 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] generic handling of NA and NaN and NULL
> 
> 
> Hello everybody
> 
> 
> I have a generic problem which the following toy function illustrates:
> 
> f <- function(n) {
>   if(abs(n) < pi) {
>     return(TRUE)
>   } else {
>     return(FALSE)
>   }
> }
>                    
> I want it to return TRUE if abs(n)<pi and FALSE otherwise.  f() is
> fine as far as it goes, but does not deal well with NA or NaN or NULL
> (I want these to signal some problem with the argument (ie return
> FALSE), but not to stop execution of f().  In particular, I want f()
> to pass R CMD check )-:
> 
> R> f(NA)
> Error in if (abs(n) < pi) { : missing value where logical needed
> 
> R> f(NULL)
> Error in abs(n) : non-numeric argument to function
> 
> 
> So, how best to patch f() up?  The best I could come up with was:
> 
> f2 <- function(n) {
>   if(is.null(n)){return(FALSE)}
>   if(is.na(n)){return(FALSE)}
>   if(abs(n) < pi) {
>     return(TRUE)
>   } else {
>     return(FALSE)
>   }
> }
> 
> This can't be the best way!  Anyway, f2() isn't right: f2(numeric(0))
> fails; note that
> 
> R> if(is.na(numeric(0))){print("asdf")}
> 
> falls over.  help.search("trap") was not very helpful.  try() doesn't
> help either:
> 
> R> try(if(1==NA){print("asdf")})
> Error in if (1 == NA) { : missing value where logical needed
> 
> 
> 
> QUESTION: how to make f() not give an error under any circumstances?
> 
> 
> 
> 
> 
> 
> -- 
> 
> Robin Hankin, Lecturer,
> School of Geography and Environmental Science
> Tamaki Campus
> Private Bag 92019 Auckland
> New Zealand
> 
> r.hankin at auckland.ac.nz
> tel 0064-9-373-7599 x6820; FAX 0064-9-373-7042
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> http://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 

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