Customize Your Own Functions

Materials adapted from Adrien Osakwe, Larisa M. Soto and Xiaoqi Xie.

1. Customize Your Own Functions

Writing functions is the best way to keep your code DRY (Don’t Repeat Yourself). If you find yourself copy-pasting code three times, it’s time to write a function.

The Anatomy of a Function

A function has three parts:

Input (Arguments): What the function needs to work (e.g., a vector of numbers).
Body: The actual code/math being performed.
Output (Return): What the function gives back to you.

# Example: Creating a manual version of the 'mean' function
new_mean <- function(values) {
  # The 'Body'
  result <- sum(values) / length(values)
  
  # The 'Return' (Output)
  return(result)
}

# Test it out
x <- 1:5
new_mean(x)

[1] 3

Pro-Tip: When to use return()

In R, the function will automatically return the very last line of code executed inside the braces. However, using the explicit return() function is a “Best Practice” because it makes it much clearer to other researchers exactly what your function is providing.