[R] Problems with NA's

[Moshe Olshansky]

The problem is that if you do the following:
x <- NA
then
x == NA
returns NA (and not TRUE or even FALSE).

Use is.na to test for NA (see ?is.na).

--- "Thomas L Jones, PhD" <jones3745 at verizon.net>
wrote:

> Difficulty handling NA's:
> Assume that I have a numeric vector y. For
> simplicity, assume that it has 10 
> elements. Assume that the third element has the
> value NA. I give it the 
> following:
> NA_test <- function (){
> y <- numeric (10)
> y [3] <- NA
> if (y [3] != NA){(print ("no")}
> print ("Leaving NA_test")
> return ()
> }# End of function
> 
>
-------------------------------------------------------------
> Unfortunately, things become confused involving the
> NA element.
> Here is the output, starting with the loading
> process:
> 
>
----------------------------------------------------------
> > NA_test <- function (){
> + y <- numeric (10)
> + y [3] <- NA
> + if (y [3] != NA){(print ("no")}
> Error: syntax error in:
> "y [3] <- NA
> if (y [3] != NA){(print ("no")}"
> > print ("Leaving NA_test")
> [1] "Leaving NA_test"
> > return ()
> Error: no function to return from, jumping to top
> level
> > }# End of function
> Error: syntax error in "}"
> >
>
---------------------------------------------------------------------
> I have enclosed the print operation in braces to
> avoid possible problems 
> with it.
> 
> Your advice?
> 
> Tom Jones
> 
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