[R] Two statement logical dealing with NAs

[David Winsemius]

On Dec 10, 2012, at 4:55 PM, Hans Thompson wrote:

> Hello.
>
> I have a two statement logical that if NA is returned for the second
> statement I want to rely on result of the first statement.  I still  
> would
> like to use both when I can though.
>
> x <- c(1:5)
> y <- c(1,2,NA,4,5)
> x < 5 & x-y == 0
>
> How can I trick R to refer back to (x < 5) where it is NA on the third
> value?

If you program so that you "trick" your tool, you will fail to  
progress in understanding it>

Since NA | TRUE returns TRUE  (and is clearly documented as such) this  
is not trickery:

 > x < 5 & (is.na(y) | x-y == 0)
[1]  TRUE  TRUE  TRUE  TRUE FALSE

-- 
David Winsemius, MD
Alameda, CA, USA