[R] Why can't R understand if(num!=NA)?

[peter dalgaard]

On May 3, 2013, at 17:24 , jpm miao wrote:

> I have a program, when I write
> 
> if(num!=NA)
> 
> it yields an error message.
> 
> However, if I write
> 
> if(is.na(num)==FALSE)
> 
> it works.
> 
> Why doesn't the first statement work?


Because comparison with an unknown value yields an unknown result. 

By the way, comparing a logical value to FALSE is silly: 

if ( !is.na(num) ) will do it.



-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com