Documentation

Why Documentation Matters

By now, you’ve called quite a few R functions: mean(), round(), sum(), install.packages(), library(), and more. Every one of those functions accepts specific arguments, in a specific order, and some of those arguments have default values you’ve been relying on without necessarily realizing it.

Do: run the code below.

See: the second line still works, even though we only gave round() one input.

Explain: round()’s second argument, digits, has a default value built in, so R uses that default whenever you don’t specify your own. But how would you know that, or know what that default value actually is, without someone telling you?

That’s exactly what documentation (also called a “help file”) is for. Every function that ships with R, and every function provided by a package distributed through CRAN, comes with documentation describing exactly what it does, what arguments it accepts, and what those arguments default to. You will refer to documentation constantly. Even experienced R users look up help files for functions they’ve used hundreds of times, just to double check an argument name or default value.

Over this tutorial, you’ll learn how to open a function’s documentation, how to read the sections it contains, and how to use that information to correctly call a function you’ve never seen before.

Quick Check

Besides looking up default argument values, what’s one other reason you might want to check a function’s documentation before using it?