Basics of R

Basics of R#

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:

image

  • 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:

image

  • 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.