[R] generic handling of NA and NaN and NULL
Liaw, Andy
andy_liaw at merck.com
Fri Feb 14 00:26:03 CET 2003
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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