Intermediate R: Functions and control flow

Session 8

September 26, 2024

Learning objectives

Write custom functions
Use if-else logic to generalize functions

Picking up from last week

Commit last week’s work to GitHub and push
Merge your work to main!
Create a new branch for today’s work and pull

Revisiting the penguins data

Note that units are in mm and g
Today we’ll convert these to imperial measurements (inches and pounds)
For this, we’ll use functions.

Functions

What are functions in R?

We use pre-written functions constantly.
Automated “recipes” for executing code
Inputs (“arguments”) and outputs

Why write our own functions?

Avoid repetition (+ mistakes)
Enhance portability + reproducibility

Writing a function objectives

Convert our data wrangling script into a function
Break this function into smaller, human-readable functions
Make this function flexible to apply to other data

Anatomy of a function

# Defining a function
# a_function will be the name of the function
# arguments go within the ()
# code goes in the curly braces

a_function <- function(an_argument) {
  # code using an_argument to produce final_output
  
  # whatever is inside return() comes out of the function
  return(final_output) 
}

# Run the code to create the function
# Then you can use it:
# a_function(<some_input>)
#

Coding time

Write a function to convert metric to imperial measurements.

Sourcing functions

You can store functions in separate R scripts and import them to your main working script.
This helps keep your main script simple and keeps your whole repo organized.
Use source(<path_to_functions_script>) in your main script.

Coding time

Save our function in a separate R script and source it from a data wrangling script.

Control flow with conditionals

What are conditionals?

Decide which action to take based on whether some condition is TRUE or FALSE
Balance readability and flexibility in scripts and functions

Conditional syntax

if(<condition>) {
  <action to take if TRUE>
}

Conditional syntax

if(<condition>) {
  <action to take if TRUE>
} else {
  <action to take if FALSE>
}

Defining conditions

== for “is equal to”
!= for “not equal to:
<, > for less than/greater than
<=, >= for less than or equal to/greater than or equal to
is.na() for is it NA?
%in% for, is this value in a vector of possibilities
…and more!

Coding time

Use conditionals to make a flexible function.

Finishing up

Commit your changes and push
Open a pull request.

Resources

Your tasks

Identify parts of your colloquium project code that could be turned into functions.
Good candidates are: repeated sections, complicated sidebars to the main flow
Convert these sections to functions and source() them to clean up the main script.