Here's a little puzzle that might shed some light on some apparently confusing behaviour by missing values (NAs) in R:
What is NA^0 in R?
You can get the answer easily by typing at the R command line:
But the interesting question that arises is: why is it 1? Most people might expect that the answer would be NA, like most expressions that include NA. But here's the trick to understanding this outcome: think of NA not as a number, but as a placeholder for a number that exists, but whose value we don't know.