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