Basic R

Question 1

Write a function drawing x times with replacement from the standard normal distribution, then taking an average and printing it

Answer 1

myfunction

Question 2

Load all functions in the R file “functions.R” in the working directory

Answer 2

source(“functions.R”)

Question 3

Show working directory

Answer 3

getwd()

Question 4

Show contents of working directory

Answer 4

dir()

Question 5

Choose working directory

Answer 5

setwd()

Question 6

Get help for the source() function

Answer 6

?source

Question 7

Find help for linear regressions

Answer 7

help.search(“linear regression”)

Question 8

What are the five atomic classes of objects

Answer 8

character, numeric, integer, complex and logical

Question 9

What is the difference between a list and a regular vector

Answer 9

The list may contain elements of different classes, the elements of a vector all have to be the same class

Question 10

Assign the integer 1 (not the number) to the object x

Answer 10

x

Question 11

Find out what class x is

Answer 11

class(x)

Question 12

Divide 1 by infinity

Answer 12

1/Inf

Question 13

Give examples of object attributes

Answer 13

Names, dimnames, dimensions, class, length, etc.

Question 14

Create an empty numeric vector x with 100 elements

Answer 14

x

Question 15

Input the letters a, b and c as elements in a vector x

Answer 15

x

Question 16

What happens if you concatenate elements of different classes?

Answer 16

They are all coerced to one class

Question 17

Make a vector consisteng of the integers 1 to 10 to a character format

Answer 17

x

Question 18

What happens if you run

x

Answer 18

NAs are introduced by coercion for the first and second elements

Question 19

Create a matrix x of zeroes with two rows and two columns

Answer 19

x

Question 20

create two vectors containing the integers 1 to 3. Merge them into a matrix as rows and into a matrix as columns

Answer 20

x

Question 21

Transform a vector containing the integers 1 to 10 into a matrix with two rows.

Answer 21

x

Question 22

What are the two types of factors and what distiguishes them?

Answer 22

Unordered (categorical, unranked), ordered (categorical, ranked)

Question 23

Why is it better to use factors than integer categories

Answer 23

They are self-describing

Question 24

Make a factor vector containing five yes/no elements. Get a frequency count of each factor level.

Answer 24

x

Question 25

What is the difference between NA and NaN?

Answer 25

NA missing values

NaN undefined mathematical operations (subset of NA)

Question 26

Test which elements in the vector x are NAs and which are NANs

Answer 26

is. na(x)
is. nan(x)

Returns logical vectors with corresponding elements TRUE if the element in the original vector is missing

Question 27

What are data frames used for?

Answer 27

1. Tabular data
2. The columns do not have to be the same class
3. The rows have names

Question 28

Create a data frame x with a “letters” column consisting of the first four letters of the alphabet and a “numbers” column consisting of the first four integers. Give the rows the names “first”, “second”, etc…

Answer 28

x

Question 29

Create a vector x with the integers from one to three. Give the elements names.

Answer 29

x

Question 30

What are the most important arguments in read.table() function?

Answer 30

file, header, sep, colClasses, nrows, skip, stringsAsFactors

Question 31

How large a dataset can you load with read.table() and read.csv()?

Answer 31

However much RAM you have available

Question 32

What is the main advantages of dump() or dput() relative to write.table() or write.csv()

Answer 32

They preserve R metadata (like class) and work better with version control applications like Git

Question 33

Save the dataframe x in a textual format that preserves metadata. Then read it into r again

Answer 33

dput(x, file=”x.R”)

dget(“x.R”)

Question 34

Save the dataframes x and y in a textual format that preserves metadata. Removet hem and then read them into r again

Answer 34

dump(c(“x”,”y”), file=”data.R”)

source(“data.R”)

Question 35

What is the main difference between dput() and dump()?

Answer 35

Dump() works on several objects, dput() only works on one. Source() will pull in the objects as they were, dget() requires you to assign them anew

Question 36

How do you get a website as text loaded into r

Answer 36

y

Question 37

What are the three subsetting operators and how are they different?

Answer 37

[ object of same type
[[ single element, class may differ, allows using calculated values, makes subsetting of a list by c( , ) sequential
$ extracts by name, does partial matching by default

Question 38

Create a vector x with the letters from a to d. Now create the vector y consisting of letters in x after b

Answer 38

x “b”]

Question 39

Create a vector x with the letters from a to d. Now create the vector y of logicals answering “y>a?” Use y to subset x

Answer 39

x “a”

x[y]

Question 40

Make a list x consisting of 1) The number from 1 to 3, 2) the letters a and b and 3) TRUE. Name the elements “num”, “let” and “log”.

Extract the first element in the list by its name, then extract as a list, then extract only its contents.

Exctract the third element of the first element

Answer 40

x = list(1:3, c(“a”,”b”), TRUE)

names(x)

Question 41

Make a vector with three words as elements. Extract the first and third word with one command.

Answer 41

x

Question 42

Make a 2x2 matrix x containing the numbers 1 to 4. Order numbers first by columns, the by rows. Subset the four, but keep it as a matrix.

Answer 42

x

Question 43

Create a vector x with numbers and NAs. Subset all non-NAs as a vector y.

Answer 43

x

Question 44

Create a data frame with two numeric variables with a few NAs. Subset out the data frame y consisting of the complete cases.

Answer 44

x

Question 45

Draw from a standard normal distribution and assign to object x. Make a logic statement that assigns 1 to y if x is above 0 and 0 to y otherwise.

Answer 45

x