1. Early warning systems
I think everyone would agree that it's best to get
advanced notice of potential problems.
2. Early warning systems
In this chapter, we'll look at standard R techniques for notifying the user.
That way, we get to avoid problems before they cause a complete failure.
Also, we'll get to handle issues - and they'll always be issues - in a sensible way.
Before we get going with notifications, we'll first think a little about the humble
Boolean operations, TRUE and FALSE. One common short-cut is to use capital T for TRUE and capital F for FALSE. But this can lead to disaster.
3. Problem 1: TRUE and FALSE
TRUE and FALSE are very special in R. They're one of the few things we
can't accidentally overwrite. For example, if we try to set TRUE equal to 5
we get an error.
4. Problem 2: TRUE and FALSE
T and F aren't protected. Now I know what you're thinking - only an ejit would
overwrite T or F. Well it can happen very easily.
Suppose you're calculating a value from the F density. Naturally, you would use F
to store the value. Unfortunately, R treats positive values as TRUE statements, leading to
potential problems!
5. Solution
We can easily side step both issues that I've mentioned. First, we
get in the habit of using TRUE and FALSE and shun the T & F shot cuts. I know this means typing
an extra few characters, but it's worth it.
Second, to test for logical values, use the function `isTRUE()`.
It works as expected when `T` is passed. But protects you against
rogue numerical values.
6. Let's have a little practice
OK, let's get started with the first lot of exercises.