Learning objectives

• Questions:

  • How to do basic arithmetics

  • How to initialize a variable

  • How to get help

• Objectives:

  • R built-in functions

• Keypoints:

  • Use RStudio to write and run R programs.

  • R has the usual arithmetic operators and mathematical functions.

  • Use <- to assign values to variables.

  • Use ls() to list the variables in a program.

  • Use rm() to delete objects in a program.

  • Use sessionInfo() to get detail of the current loaded environment and packages

Input to R

• In R console, the symbol > stands for R prompt.

• The # is for comment insert.

• To clean the existing environment, remove all memory in previous sessions:

> rm(list=ls())

Using R as calculator

• When using R as a calculator, the order of operations is the same as you would have learned back in school.

• From highest to lowest precedence:

  • Parentheses: (, )

  • Exponents: ^ or **

  • Multiply: *

  • Divide: /

  • Add: +

  • Subtract: -

  • Other math functions: sin, cos, log(), log10(), exp

a <- (1+2)*3-4^5
b <- sin(1)+log10(20)*exp(2)

Comparisons in R

• ==: equality

• !=: inequality

• <& <=: less than & less than or equal to

• >& >=: more than & more than or equal to

1==1

Assign Variables

• To assign variable in R, we can use both <- and = sign

a <- 1
b = 2

• Note that assignment does not print out value to R console. It saves the variable in Environment section:

• To print the variable to console

a
print(a)

• The output will be like this:

> a
[1] 1
> print(a)
[1] 1

• Do not to worry about the [1] in front. We will be learning about that later.

Working directory

One important step in R is to define the working directory. It is particularly useful when you are working with files in the working directory and working in Linux environment in Palmetto:

# print working directory
getwd()
# set working directory on your local computers
setwd('C:/R/') # for Windows
setwd('/user/home/R') # for Macs

Seeking Help

• In order to look for help files for function:

  • Put ? in front of function name, for example rnorm

?rnorm
help(rnorm)
str(rnorm)

• The help section will display:

• If you don’t kow the exact function name, you can use ?? and R will try to find the appropriate function for you. For example, I want to know how to compute a correlation coefficient. I can do ??correlation, and it will give me a list of functions that are, one way or another, related to correlation, and the first result on the list is the function corr, which is Pearson’s correlation coefficient.