Functions

Nicky Wakim

What are functions?

• R has many built-in functions that allow you to perform a variety of tasks

• Functions usually take the form:

function_name(
  argument1 = input_value1,
  argument2 = input_value2,
  ...
  )

1

function_name is the name of the function we are using.

2

Within the parentheses of the function, there are set arguments that we assign values to.

Example: simple function like mean()

• mean() is a function that generates the calculated mean of a set of numbers
• It has one main argument: x
• Output (automatically printed) will be the mean of the numbers in x

mean(
  x = c(1, 2, 3, 4, 5, 6)
)

1

The argument x is assigned the value of a vector of numbers (1, 2, 3, 4, 5)

[1] 3.5

Example: calling the seq() function

• seq() is a function that generates a sequence of numbers.
• It has three arguments: from, to, and by
• Output will be the sequence numbers

seq(
  from = 1,
  to = 10,
  by = 2
)

1

The argument from is assigned the value of 1, which is the starting point of the sequence.

2

The argument to is assigned the value of 10, which is the ending point of the sequence.

3

The argument by is assigned the value of 2, which specifies the increment between numbers in the sequence.

[1] 1 3 5 7 9

We don’t need to specify the argument names

• We can run seq() without the argument names
• R will assume that the values are in the correct order of the arguments

 

We get the same result:

seq(1, 10, 2)

[1] 1 3 5 7 9

Output of a function

• We can also assign the output of a function to an object using the assignment operator <-:

function_output <- function_name(
  argument1 = input_value1,
  argument2 = input_value2,
  ...
  )                                     

1

The output of function_name is assigned to an object called function_output

2

Within the parentheses of the function, there are set arguments that we assign values to.

• The output will not print, but it will be stored in the object function_output

Now with the seq() function

• We will assign the output of the seq() function to an object called odds:

odds <- seq(
  from = 1, 
  to = 10, 
  by = 2
)

• So odds will now contain the sequence (1,3,5,7,9)

Help with functions

• If you need a reminder of how to use a function, you can use the ? or ?? to access the help file for that function:

?seq
??read_sas

1

The ? will take you to the help file for the seq() function, which will show you the arguments and how to use it.

2

The ?? will search for any functions read_sas from your installed packages and show you a list of functions that match that search term. This is helpful when you don’t remember the package a function is in.

 

• Certain functions will show you the arguments if you press Tab after typing the function name and parentheses

mean()
sd()

 

• R will also help autofill the names of functions from your loaded packages:

m
s