Example 07: Functions and Iteration

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library(broom)

Writing Functions

I mentioned in class that my add function didn’t have any error handling or guard clauses. Here’s an example of why it’s worth adding them.

my_adder <- function(x, add = 1) {
  x + add
}

my_adder(10)

[1] 11

my_adder(1:10)

 [1]  2  3  4  5  6  7  8  9 10 11

# This won't work
# my_adder("a")

Guard clauses and error handling:

my_adder <- function(x, add = 1) {
  if(!is.numeric(x)) {
    return("Argument `x` must be numeric.")
  }

  x + add
}

my_adder("a")

[1] "Argument `x` must be numeric."

my_adder <- function(x, add = 1) {
  if(!is.numeric(x)) {
    return("Argument `x` must be numeric.")
  }

  if(!is.numeric(add)) {
    return("Argument `add` must be numeric.")
  }

  x + add
}

Here I use return() in the guard clauses in order to make this example work as part of the pipeline that creates the site. But really I should use stop().

my_adder(1:10, 5)

 [1]  6  7  8  9 10 11 12 13 14 15

my_adder(1:10, "c")

[1] "Argument `add` must be numeric."

One small point here: resist using else in clauses like this. Just use if to check a condition and if it fails, exit the function. The “happy path” is one that passes your guard clauses. Other paths should exit with an informative message.