Functions

When we first learn to code, we often start by working within a console, and experiment by writing one line, executing it, inspecting the output, then writing another, executing that, etc. We then might graduate to writing several lines of code at once in a script, and then executing the script, and inspecting the final output. This might work well for a while, but as we find ourselves writing longer and longer more complex scripts, there can be a great deal of code repetition, and perhaps even copy-pasting of similar code blocks.

The problem with sticking with this approach is that our scripts quickly become unreadable and inflexible. Moreover, we can easily introduce bugs during the copy-paste-replace cycle. The solution is to use functions.

Functions package a unit of code that can be used and reused in some sequence to get a result or produce an effect. Ideally, functions are simple (easy to understand, returns only one output), and modular. We recommend you read this book chapter about writing functions (whether or not you code in R specifically). It motivates the use of functions and outlines many basic principles about writing good ones.

Recommendations and resources

Language	Resources
R	Writing functions in R
Python	Writing functions in Python