Sequences, Vectors, Matrices, and Data Frames

Question 1

Create a sequence of numbers from a to b

Answer 1

a:b or seq(a, b)

Question 2

Create a sequence of numbers from 1 to 10, incremented by 0.5

Answer 2

seq(1, 10, by=0.5)

Question 3

Get the length of a sequence

Answer 3

length(sequence)

Question 4

Make a vector with 10 repetitions of the vector (0, 1, 2)

Answer 4

rep(c(0, 1, 2), times = 10)

Question 5

Make a vector that repeats 10 zeros, then 10 ones, then 10 twos

Answer 5

rep(c(0, 1, 2), each=10)

Question 6

What are the 2 types of vectors?

Answer 6

atomic vectors = contain one data type lists = can contain multiple data types

Question 7

Conditional expressions: symbol for OR symbol for AND

Answer 7

or: A | B
and: A & B

Note that AND operators get evaluated before OR operators

Question 8

Join together the elements in the following vector: c(“My”, “name”, “is”)

Answer 8

paste(c(“My”, “name”, “is”), collapse= “ “) #collapse tells R that want spaces between characters when join together

Question 9

Add an element to this vector: my_char = c(“My”, “name”, “is”)

Answer 9

c(my_char, “Estefy”)

Question 10

Join “Hello” and “world” with a space between words

Answer 10

paste(“Hello”, “world”, sep = “ “)

Question 11

Generate the following output: A-1, B-2, C-3 Use vectors 1:3 and c(“A”, “B”, “C”)

Answer 11

paste(c(“A”, “B”, “C”), 1:3)

Question 12

What do mathematical operations involving NA yield?

Answer 12

NA

Question 13

Which function tells you whether each element of a vector is NA?

Answer 13

is.na(dataset) #It generates a vector of booleans with TRUE for missing values

Question 14

Count the number of missing values in my_na = is.na(dataset)

Answer 14

sum(my_na) This will add up the boolean array where TRUE = 1 and FALSE = 0, giving number of missing values

Question 15

Make a vector of all non-missing values in vector x

Answer 15

x[!is.na(x)]

Question 16

Make a vector with the 3rd and 5th elements of vector x

Make a vector with all the elements of x except for the 3rd and 5th elements

Answer 16

x[c(3, 5)]

x[c(-3, -5)] or x[-c(3, 5)]

Question 17

Create a numeric vector with 3 named elements:

foo=11

bar =2

norf= NA

Print the names of the vector

Answer 17

vect <- c(foo = 11, bar = 2, norf = NA)

names(vect)

Output: “foo” “bar” “norf”

Question 18

Add names to vector = c(1, 2, 3)

names: “hey”, “there”, “you”

Answer 18

names(vector) <- c(“hey”, “there”, “you”)

Question 19

How do you check if two vectors are the same?

Answer 19

identical(vector1, vector2)

Output will be true or false

Question 20

True or False

Matrices can contain many different classes of data

data frames can contain many different classes of data

Answer 20

FALSE: matrices can only contain a single class of data

TRUE: data frames can contain many different classes of data

Question 21

add dimension 4, 5 to a vector x

Answer 21

dim(x) <- c(4, 5)

Question 22

Create a matrix with the numbers from 1 to 20 with 4 rows and 5 columns

Add row names to the matrix: “one”, “two”, “three”, “four”

Create a data frame with row names and matrix

Add column names to the data frame: “One”, “Two”, “Three”, “Four”, “Five”

Answer 22

my_matrix <- matrix(1:20, nrow=4, ncol=5)

names = c(“one”, “two”, “three”, “four”)

cbind(names, my_matrix)

Note that this will coerce all numbers into characters

my_data <- data.frame(names, my_matrix)

cnames <- c(“One”, “Two”, “Three”, “Four”, “Five”)

colnames(my_data) <- cnames

Question 23

TRUE function

exclusive OR function

Answer 23

xor() returns true if one argument is TRUE and the other one is FALSE, otherwise, it will return FALSE

isTrue(expression)

xor(expression1, expression2)

Question 24

Add the rows of my_matrix

Add the columns of my_matrix

Answer 24

rowSums(my_matrix)

colSums(my_matrix)

Question 25

add matrix2 to matrix 1 as columns

add matrix2 as rows to matrix1

Answer 25

cbind(matrix1, matrix2)

rbind(matrix1, matrix2)