R

Question 1

assign a value to a variable

Answer 1

use

Question 2

determining that the object (murders dataset) is of the “data frame” class

Answer 2

class(murders)

Question 3

finding out more about the structure of the object

Answer 3

str(murders)

Question 4

showing the first 6 lines of the dataset

Answer 4

head(murders)

Question 5

obtain a specific column (ex population)

Answer 5

murders$population

$ is called accessor operator

Question 6

displaying the variable names in the murders dataset

Answer 6

names(murders)

Question 7

determining how many entries are in a vector

Answer 7

pop

Question 8

obtaining the levels of a factor

Answer 8

levels(murders$region)

Question 9

obtaining the number of levels of a factor

Answer 9

nlevels()

Question 10

create vectors of class numeric or character

Answer 10

use “concentrate function”

ex: codes

Question 11

name the elements of a numeric vector

Answer 11

codes

Question 12

name the elements of a numeric vector in a different way

Answer 12

codes

Question 13

access specific elements of a vector

Answer 13

Using square brackets

Question 14

The function ____ sorts a vector in increasing order.

Answer 14

sort()

Question 15

The function _____ produces the indices needed to obtain the sorted vector

Answer 15

order()

Question 16

The function ____ gives us the ranks of the items in the original vector

Answer 16

rank()

Question 17

The function ____ returns the largest/smallest value

Answer 17

max() and min()

Question 18

The function ____ returns the index of the largest/smallest value

Answer 18

which.max() and which.min()

Question 19

The name of the state with the maximum population is found by doing ??

Answer 19

murders$state[which.max(murders$population)]

Question 20

how to obtain the murder rate

Answer 20

murder_rate

Question 21

ordering the states by murder rate, in decreasing order

Answer 21

murders$state[order(murder_rate, decreasing=TRUE)]

Question 22

Creating a logical vector that specifies if the murder rate in that state is less than or equal to 0.71

Answer 22

index

Question 23

Determining which states have murder rates less than or equal to 0.71

Answer 23

murders$state[index]

Question 24

Calculating how many states have a murder rate less than or equal to 0.71

Answer 24

sum(index)

Question 25

efining an index and identifying states with both conditions true

Answer 25

# creating the two logical vectors representing our conditions
west

Question 26

The function _______ gives us the entries of a logical vector that are true.

Answer 26

which()

Question 27

The function _______ looks for entries in a vector and returns the index needed to access them.

Answer 27

match()

Question 28

if we want to know whether or not each element of a first vector is in a second vector

Answer 28

function %in%

Question 29

Change a data table by adding a new column, or changing an existing one

Answer 29

dplyr package:

mutate() function

Question 30

To filter the data by subsetting rows

Answer 30

dplyr package:
function filter()

Question 31

To subset the data by selecting specific columns

Answer 31

dplyr package:

select() function

Question 32

To perform a series of operations by sending the results of one function to another function

Answer 32

using the pipe operator, %>%.

murders %>% select(state, region, rate) %>% filter(rate <= 0.71)

Question 33

create data frames

Answer 33

data.frame()
By default, the data.frame() function turns characters into factors. To avoid this, we utilize the stringsAsFactors argument and set it equal to false.

Question 34

create a simple scatterplot 
# a simple scatterplot of total murders versus population

Answer 34

function plot()
x

Question 35

Histograms. Ex: a histogram of murder rates

Answer 35

hist()

hist(murders$rate)

Question 36

Boxplots. Ex: the rate per region in the murders dataset

Answer 36

boxplot()

boxplot(rate~region, data = murders)

Question 37

works on vectors by examining each element of the vector and returning a corresponding answer accordingly.

Answer 37

ifelse() function

Question 38

takes a vector of logicals and returns true if any of the entries are true

Answer 38

any()

Question 39

takes a vector of logicals and returns true if all of the entries are true

Answer 39

all()

Question 40

define a new function

Answer 40

function()

Question 41

general form of a for-loop

Answer 41

For i in [some range], do operations
for(i in 1:5){
print(i)