NA - Not Available/Not applicable is R’s way of denoting empty or missing values. When doing comparisons - such as equal to, greater than, etc. - extra care and thought needs to go into how missing values (NAs) are handled. More explanations about this can be found in the Chapter 2: R basics of our book that is freely available at the HealthyR website
This post lists a couple of different ways of keeping or discarding rows based on how important the variables with missing values are to you.
