R Reference

Basic Operation

# this is a comment in R
Use x <- 3 to assign a value, 3, to a variable, x
R counts from 1, unlike many other programming languages (e.g., Python)
length(thing) produces the length of a collection
c(value1, value2, value3) creates a vector
container[i] selects the i’th element from the container

List objects in current environment ls()

Remove objects in current environment rm(x)

Remove all objects from current environment rm(list = ls())

Control Flow

Create a contitional using if, elif, and else

if(x > 0){
    print("value is positive")
} else if (x < 0){
    print("value is negative")
} else{
    print("value is neither positive nor negative")
}

create a for loop to process elements in a collection one at a time
```
for (i in 1:5) {
    print(i)
}
```

This will print:

Use == to test for equality
3 == 3, will return TRUE,
'apple' == 'orange' will return FALSE
X & Y is True is both X and Y are true
X | Y is True if either X or Y, or both are true

Functions

Defining a function:

is_positive <- function(integer_value){
    if(interver_value > 0){
       TRUE
    else{
       FALSE
    {
}

In R, the last executed line of a function is automatically returned

Specifying a default value for a function argrment

increment_me <- function(value_to_increment, value_to_increment_by = 1){
    value_to_increment + value_to_increment_by
}

increment_me(4), will return 5

intrement_me(4, 6), will return 10

Call a function by using function_name(function_arguments)
- apply family of functions:
```
apply()
sapply()
lapply()
mapply()
```

apply(dat, MARGIN = 2, mean) will return the average (mean) of each column in dat

Packages

Install package by using install.packages("package-name")
Update packages by using update.packages("package-name")
Load packages by using library("package-name")