Functions

Calling functions

R has a large collection of built-in functions that are called using:

function_name(arg1 = val1, arg2 = val2, ...)

Let's try using seq() which makes regular sequences of numbers and, while we're at it, learn more helpful features of RStudio. Type se and hit TAB. A popup shows you possible completions. Specify seq() by typing more (a "q") to disambiguate or by using ↑/↓ arrows to select. Notice the floating tooltip that pops up, reminding you of the function's arguments and purpose. If you want more help, press F1 to get all the details in the help tab in the lower right pane.

Press TAB once more when you've selected the function you want. RStudio will add a matching opening (() and closing ()) parentheses for you. Type the arguments 1, 10 and hit return.

seq(1, 10)
 #>  [1]  1  2  3  4  5  6  7  8  9 10

Type this code and notice you get similar assistance with the paired quotation marks:

x <- "hello world"

Quotation marks and parentheses must always come in a pair. RStudio does its best to help you, but it's still possible to mess up and end up with a mismatch. 

If this happens, R will show you the continuation character "+":

> x <- "hello
+

The + says that R is waiting for more input.  Usually, that means you've forgotten either a " or a ). Either add the missing pair or press ESCAPE to abort the expression and try again.

If you make an assignment, you do not see the value, and you are then tempted to double-check the result immediately:

y <- seq(1, 10, length.out = 5)
 y
 #> [1]  1.00  3.25  5.50  7.75 10.00

This common action can be shortened by surrounding the assignment with parentheses, which causes the assignment and "print to screen" to happen.

(y <- seq(1, 10, length.out = 5))
 #> [1]  1.00  3.25  5.50  7.75 10.00

Now look at your environment in the upper right pane:

Here you can see all of the objects that you've created.

Source: H. Wickham and G. Grolemund, https://r4ds.had.co.nz/workflow-basics.html
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Getting help with functions and features

R has an inbuilt help facility similar to the man facility of UNIX. To get more information on any specific named function, for example solve, the command is

> help(solve)

An alternative is

> ?solve

For a feature specified by special characters, the argument must be enclosed in double or single quotes, making it a "character string": This is also necessary for a few words with syntactic meaning including if, for and function.

> help("[[")

Either form of quote mark may be used to escape the other, as in the string "It's important". Our convention is to use double quote marks for preference.

On most R installations help is available in HTML format by running

> help.start()

which will launch a Web browser that allows the help pages to be browsed with hyperlinks. On UNIX, subsequent help requests are sent to the HTML-based help system. The ‘Search Engine and Keywords' link in the page loaded by help.start() is particularly useful as it is contains a high-level concept list which searches though available functions. It can be a great way to get your bearings quickly and to understand the breadth of what R has to offer.

The help.search command (alternatively ??) allows searching for help in various ways. For example,

> ??solve

Try ?help.search for details and more examples.

The examples on a help topic can normally be run by

> example(topic)

Windows versions of R have other optional help systems: use

> ?help

for further details.

Source: R Core Team, https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Getting-help
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License.