3.3 Literate programming and RMarkdown | CS5702 Modern Data Book

Tags

Top Highlights

• User defined functions offer many advantages including - abstraction, i.e., the ability to hide details to help understandability e.g., checkInput() - placing related code in one place - reuse and avoiding lots of copy-and-paste type coding - maintainability i.e., the need to only make changes in one place in the event of an error or update in required functionality

• In R, the return value of a function is always the very last expression that is evaluated. Because the num variable is the last expression that is evaluated in this function, that becomes the return value of the function. Note that there is a return() function that can be used to return an explicitly value from a function. If in doubt we recommend using return() since it makes the intentions of the function developer absolutely clear. While we are at it, triple is a far more descriptive name than myFunction.

• The term “literate programming” was coined by Donald Knuth Knuth (1984) based on the idea that a computer program should be documented in a manner such that it is readable by humans.

• Instead of imagining that our main task is to instruct a computer what to do, let us concentrate rather on explaining to human beings what we want the computer to do. – (Knuth 1984)

• His ideas are encapsulated in three principles (although of course there is a lot more detail in his paper):

• move away from writing programs to ‘please’ the computer instead, focus on communication and understanding create a single document to integrate data analysis (executable code) with textual documentation, linking data, code, and explanation

• Readable code tips include (Wickham 2012) names comments layout e.g., indentation and spacing prettyprinting user-defined functions

• One of the best ways to improve your reach as a data scientist is to write functions. Functions allow you to automate common tasks in a more powerful and general way than copy-and-pasting. — (Grolemund and Wickham 2018)

• User defined functions offer many advantages including - abstraction, i.e., the ability to hide details to help understandability e.g., checkInput() - placing related code in one place - reuse and avoiding lots of copy-and-paste type coding - maintainability i.e., the need to only make changes in one place in the event of an error or update in required functionality

• When calling or using the above function, the user must specify the value of the argument num.

• If an argument is not specified by the user, R will throw an error. But on occasions this can be burdensome, especially if there are many arguments with common or sensible default values. Then we can specify the default value (which is taken if no argument is explicitly provided) in the function definition. So, for example, for triple() we could say zero is the default if no value for num is given by the function caller.