# Functions

## Learning Objectives

• Built-in Functions
• User-built functions
• Extensions

# Built-in Functions

## Built-in Functions

There are several available functions in R to conduct specific statistical methods or tasks

## Help Documentation

Section Description
Description Provides a brief introduction of the function
Usage Provides potential usage of the function
Arguments Arguments that the function can take
Details An in depth description of the function
Value Provides information of the output produced by the function
Notes Any need to know information about the function
Authors Developers of the function
References References to the model and function
Examples Examples of the function

## Generic Functions

Several R objects have a known class attached to it. A specialized object designed to be read by generic functions, such as summary() and plot().

For example, the summary() is a generic for several types of functions: summary.aov(), summary.lm(), summary.glm(), and many more.

## Commonly-used Function

Functions Description
aov() Fits an ANOVA Model
lm() Fits a linear model
glm() Fits a general linear model
t.test() Conducts a t-test

# User-built functions

## User-built functions

• Functions created by the user for analysis

• Needs to be ran once to the R environment

• Will be lost when R session is closed

## Anatomy

name_of_function <- function(data_1, data_2 = NULL,
argument_1, argument_2 = TRUE, argument_3 = NULL,
...){
return(output_object)
}
• function: used to construct the function

• data1: first data argument that needs to supplied

• data2: second data argument that does not need to be supplied

• argument1: first argument must be supplied to alter function

• argument2: second argument to alter function, set to TRUE

• argument3: third argument that does not need to be supplied

• …: additional arguments supplied to other functions

## Example

Create a function for

$y = \ln(x^2)$

## Example

Create a function for

$f(x) = \left\{\begin{array}{cc} x^3 & x<0\\ x^2 + 5 & \mathrm{otherwise} \end{array} \right.$

## Example

Create a function for

$f(x,y) = \left\{\begin{array}{cc} x^3 e^y & x<0\ \\ x^2 + 5 + \ln(y) & \mathrm{otherwise} \end{array} \right.$

## Example

Create the function that allows your to compute the z-score of a specific value x using the sampling distribution from a set of data (y vector):

$z = \frac{x-\bar y}{\sqrt{s^2_{y}/n_y}}$

# Extensions

## R Packages

R Packages are used to utilize functions created from the community.

### Installation

install.packages("tidyverse")

library(tidyverse)