Chapter 3 Lab 2: Basic R Programming and Vector Operations

Objectives:

  1. To understand what an object is in R
  2. To identify and create vectors
  3. To learn how to differentiate types (classes) of vectors
  4. To perform simple math operations on numeric vectors

This chapter focuses on getting comfortable with the R console, scripting, and packages, and on the core syntax you will use for the rest of the course: creating objects, and building and operating on vectors.

3.1 The R console and basic math

Open RStudio and locate the console pane. You can type any of the following directly into the console and hit Enter:

2 + 2
## [1] 4
10 - 3
## [1] 7
6 * 7
## [1] 42
100 / 4
## [1] 25
2^5
## [1] 32

R follows the standard order of operations (PEMDAS), and you can use parentheses to control it, just like a calculator.

Question 1

  • Use the R console to calculate the area of a circle with radius 4.5 (Hint: pi is a built-in constant in R)
  • Calculate (12+8)/4^2 using R. Add the code and the result.

3.2 Objects

R can store any type of variable into an object. To create an object, write the name of the object, followed by <-, followed by what you want to store.

x <- 5
x
## [1] 5

You’ll see the new object x appear in your Environment pane (upper right of RStudio). That confirms your object has been created and is available for future use in this session.

3.3 Basic data structures in R

A basic data structure is an n-dimensional object that stores information. Data structures in R are classified by their number of dimensions:

  1. Uni-dimensional data structures such as vectors
  2. Two-dimensional data structures such as data frames or matrices
  3. N-dimensional data structures such as lists (not covered in this course)
# One dimensional objects
c(1,2,3,4,5)
## [1] 1 2 3 4 5
c("A","B","C","D","E")
## [1] "A" "B" "C" "D" "E"
# Two dimensional objects
data.frame(c(1,2,3,4,5), c("A","B","C","D","E"))
##   c.1..2..3..4..5. c..A....B....C....D....E..
## 1                1                          A
## 2                2                          B
## 3                3                          C
## 4                4                          D
## 5                5                          E

3.4 Unidimensional objects: Vectors

A vector is a one-dimensional object — think of it as a “list” of elements in only one direction, with no rows or columns.

numbers <- c(1,2,3,4,5)
letters_vec <- c("A","B","C","D")
numbers
## [1] 1 2 3 4 5
letters_vec
## [1] "A" "B" "C" "D"

To create a vector, use the c() function (short for “combine”), which combines the values you separate by commas.

R Functions

Functions are the commands R uses to interpret an order. c() means “Combine Values into a Vector.”

Syntax: function(object)

To measure the length of a vector, use the function length(): 

length(numbers)
## [1] 5

Question 2

  • Create three vectors:
    • One named words with your five favorite words
    • One named numbers with your lucky numbers
    • One named mixed with three numbers and three letters, in any order
  • Show the code you used to create the vectors

3.4.1 Classes of vectors

Use the class() command to identify the type of vector you’re working with:

class(numbers)
## [1] "numeric"
class(letters_vec)
## [1] "character"

R shows either numeric/integer or character. Character vectors are surrounded by quotation marks ("); numeric vectors are not.

Question 3

  • What are the classes of your words, numbers and mixed objects from Question 2?
  • What class does R assign to a vector that mixes numbers and letters, like mixed? Why do you think that happens?

3.5 Math operations on vectors

Because vectors can hold multiple numbers at once, math operations are applied element-wise:

v1 <- c(1, 2, 3, 4, 5)
v1 + 10
## [1] 11 12 13 14 15
v1 * 2
## [1]  2  4  6  8 10
v1 ^ 2
## [1]  1  4  9 16 25

You can also do math between two vectors of the same length:

v2 <- c(10, 20, 30, 40, 50)
v1 + v2
## [1] 11 22 33 44 55
v2 / v1
## [1] 10 10 10 10 10

Useful summary functions for numeric vectors:

sum(v1)
## [1] 15
mean(v1)
## [1] 3
max(v1)
## [1] 5
min(v1)
## [1] 1

Question 4

  • Create a numeric vector called measurements with 6 numbers of your choice
  • Calculate the sum, mean, maximum, and minimum of measurements. Add the code and results
  • Multiply every value in measurements by 2.54 (as if converting inches to centimeters). Add the code and the resulting vector

3.6 Expanding vectors

If you have two vectors of the same class, you can combine them using c() again:

double.letters <- c(letters_vec, letters_vec)
double.letters
## [1] "A" "B" "C" "D" "A" "B" "C" "D"
double.numbers <- c(numbers, numbers)
double.numbers
##  [1] 1 2 3 4 5 1 2 3 4 5
more.numbers <- c(numbers, 6, 7, 8, 9, 10)
more.numbers
##  [1]  1  2  3  4  5  6  7  8  9 10

Question 5

  • Increase each of your vectors from Question 2 by two or three more elements. Add the code and the results.
  • Create an object that combines your words and numbers vectors. Add the code.
  • What is the class of this combined object? Explain why, based on what you learned in Question 3.