Assignments

Question 1

What happens if you do the following:
c(1,2,3,4) + c(5,15) ?

Answer 1

The second vector is recycled, so you get
6 17 8 19

Question 2

What does the upward arrow do in Rstudio?

Answer 2

It gives the previous command

Question 3

What does the tab do?

Answer 3

It gives suggestions when you start typing a name of a variable.

Question 4

How do you change your working directory?

Answer 4

setwd(‘name’) sets the current working directory to the directory with that name.

Question 5

How do you ask for help/info about a function?

Answer 5

Put a ‘?’ in front of it and remove the parentheses.
Example: ?file.exists for the file.exists() function.

Question 6

How do you get the current working directory?

Answer 6

getwd()

Question 7

How do you get a list of all the objects in the current workspace?

Answer 7

ls()

Question 8

How do you get a list of the files in the current working directory?

Answer 8

list.files()

Question 9

How do you create a new directory?

Answer 9

dir.create(‘name’)

Question 10

How do you check if a file exists?

Answer 10

file.exists(‘name’)

Question 11

How do you create a new filepath name that can be used across platforms?

Answer 11

file.path(‘a’, ‘b’)

Question 12

How do you create a directory within a directory?

Answer 12

dir.create((‘nametop’, ‘namenested’), recursive = TRUE)

Question 13

How do you get a sequence of the numbers 1 to 20, including 1 and 20?

Answer 13

1:20 or seq(1,20)

Question 14

What happens when you use seq(x,y) with real numbers?

Answer 14

It gives the sequence from x to y (inclusive) with increments of 1. May never reach y

Question 15

How do you get help/info about an operator like : ?

Answer 15

? :
So put the operator between back ‘s

Question 16

How do you adjust the increments when creating a sequence of numbers from x to y?

Answer 16

seq(x,y, by = z)
With z the size of increment.

Question 17

What command do you give if you want a sequence of 30 numbers between 5 and 10?

Answer 17

seq(5, 10, length=30)

Question 18

What is the best way to get a sequence of numbers with the same length as a vector variable?

Answer 18

seq.along(variablename)

Question 19

How do you get the length of a variable?

Answer 19

length(variable)

Question 20

How do you create a vector of thirty zeros?

Answer 20

rep(0, times=30)

Question 21

How do you create a vector that repeats the pattern 0 1 2 ten times?

Answer 21

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

Question 22

How do you create a vector with ten 0s, ten 1s and ten 2s?

Answer 22

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

Question 23

What are the two types of vectors?

Answer 23

Atomic vectors and lists.

Question 24

Atomatic vector

Answer 24

Vector that contains only one data type

Question 25

Logical vectors

Answer 25

Atomatic vectors that can be only TRUE, FALSE or NA (not available).

Question 26

What do you use to create a character vector?

Answer 26

Double quotes: “x”.

Question 27

How do you concatenate and print the elements of a given character vector?

Answer 27

paste(vectorname, collapse=” “)

Question 28

How do you join two character vectors v1 and v2?

Answer 28

paste(v1, v2, sep=” “)

Question 29

What is LETTERS in R?

Answer 29

A predefined character vector that contains all 26 letters of the alphabet.

Question 30

What happens when you use the paste() function on a number vector?

Answer 30

It transforms the numbers to characters, so the program will read them as chars.

Question 31

What does NA represent?

Answer 31

A missing value.

Question 32

What does an operation involving NA result in?

Answer 32

NA

Question 33

How can you make a vector of 100 random values out of two other vectors?

Answer 33

sample(c(v1,v2),100)

Question 34

What does is.na(vector) do?

Answer 34

It creates a vector with all the values in the vector that are NA.

Question 35

How does R represent TRUE and FALSE?

Answer 35

By 1 and 0.

Question 36

What happens if you get the sum of all logical values in R?

Answer 36

You essentially get the number of TRUE values, since these are 1.

Question 37

How do you get the sum of all values of a vector?

Answer 37

sum(…)

Question 38

What does NaN stand for?

Answer 38

not a number

Question 39

What does inf stand for?

Answer 39

infinity

Question 40

How do you retrieve a subset from a vector?

Answer 40

vectorname[0:10] for slice 0:10.

Question 41

What are the four kinds of index vectors?

Answer 41

1. Logical vectors
2. Vectors of positive integers
3. Vectors of negative integers
4. Character vectors

Question 42

What does x[is.na(x)] do?

Answer 42

It gives a vector containing all NAs from x.

Question 43

How do you get for example the 3rd, 5th and 7th element from a vector?

Answer 43

vectorname[c(3,5,7)].

Question 44

How do you get all elements of vector v except the second element?

Answer 44

v[c(-2)]

Question 45

What is a name vector?

Answer 45

A vector that contains both names and numbers, kind of like a 2d vector.

Question 46

How can you give names to a vector v with only numbers?

Answer 46

names(v) <- c(“name a”, “name b”, … )

Question 47

How do you check whether two vectors are the same?

Answer 47

Identical(v1,v2)

Question 48

What is the difference between a matrix and a data.frame?

Answer 48

A matrix can only contain one class of data, a data.frame can contain multiple.

Question 49

How do you get the dimensions of an object x?

Answer 49

dim(x)

Question 50

How do you get the class of an object?

Answer 50

class(x)

Question 51

How do you make a matrix of r rows and c columns, containing numbers 1 through 20?

Answer 51

matrix(data=seq(1,20), nrows = r, ncol =c)

Question 52

What does cbind() do?

Answer 52

It combines the columns of for example a vector and a matrix. Implicit coercion then happens.

Question 53

What you need to do if you want to combine different data types?

Answer 53

Use data.frame(vector, matrix)

Question 54

What is the difference between && and &, | and || ?

Answer 54

The double one && / || evaluates only the first element of a vector whilst the single one & / | evaluates all elements.

Question 55

How do you use a function for checking boolean value?

Answer 55

isTRUE(x)

Question 56

What is the function for exclusive or?

Answer 56

xor(x)

Question 57

What does which(x) do?

Answer 57

It finds the indices of the object that satisfy the constraint, for example which(vector1 >5) gives indices of elements of vector1 that are bigger than 5.

Question 58

How do you get a preview of a dataset saved in a data.frame?

Answer 58

head(x) for the first 6 rows, tail(x) for the last. Use argument n=x for x amount of rows.

Question 59

What two functions can you use to get an overview of the data in an object?

Answer 59

summary(x) or str(x).

Question 60

How do you clear an R script from all variables?

Answer 60

rm(list=ls())

Question 61

How do you clear all the graphs from memory in R?

Answer 61

graphics.off()