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:

	1
	2
	3
	4
	5

• 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")