6SPECIAL VALUES, CLASSES, AND COERCION
You’ve now learned about numeric values, logicals, character strings, and factors, as well as their unique properties and applications. Now you’ll look at some special values in R that aren’t as well-defined. You’ll see how they might come about and how to handle and test for them. Then you’ll look at different data types in R and some general object class concepts.
6.1 Some Special Values
Many situations in R call for special values. For example, when a data set has missing observations or when a practically infinite number is calculated, the software has some unique terms that it reserves for these situations. ...