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

[David Winsemius]

On May 3, 2013, at 10:46 AM, peter dalgaard wrote:

> 
> 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. 

Anything else would violate the Second Law of Thermodynamics. We cannot have comparisons reducing entropy, now can we? Uncertainty cannot run uphill.

-- 
David Winsemius
Alameda, CA, USA