Custom error logic

Sometimes the assert_*() functions in assertive don't give the most informative error message. For example, the assertions that check if a number is in a numeric range will tell the user that a value is out of range, but the won't say why that's a problem. In that case, you can use the is_*() functions in conjunction with messages, warnings, or errors to define custom feedback.

The harmonic mean only makes sense when x has all positive values. (Try calculating the harmonic mean of one and minus one to see why.) Make sure your users know this!

This exercise is part of the course

Introduction to Writing Functions in R

View Course

Exercise instructions

If any values of x are non-positive (ignoring NAs) then throw an error.
Look at what happens when you pass a character argument to calc_harmonic_mean().

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

calc_harmonic_mean <- function(x, na.rm = FALSE) {
  assert_is_numeric(x)
  # Check if any values of x are non-positive
  if(___(___(___), na.rm = TRUE)) {
    # Throw an error
    ___("x contains non-positive values, so the harmonic mean makes no sense.")
  }
  x %>%
    get_reciprocal() %>%
    mean(na.rm = na.rm) %>%
    get_reciprocal()
}

# See what happens when you pass it negative numbers
calc_harmonic_mean(std_and_poor500$pe_ratio - 20)

Edit and Run Code