R Basic

Question 1

What does IDE stand for?

Answer 1

Interactive Development Environment

Question 2

FUNCTION: install a package in R

Answer 2

install.packages (“packagename”)

Question 3

FUNCTION: load and attach an R Package to a session

Answer 3

Library (packagename)

Question 4

FUNCTION: List of objects

Answer 4

ls()

Question 5

FUNCTION: square root

Answer 5

sqrt

Question 6

FUNCTION: find the object data type

Answer 6

class(object)

Question 7

What is a data frame?

Answer 7

a table

Question 8

FUNCTION: load a data set

Answer 8

data(“data set name”)

Question 9

What is the $ called?

Answer 9

the accessor

Question 10

What is an accessor?

Answer 10

a function that allows a user to interact with slots of an object

Question 11

== is what

Answer 11

logical operator, will be true or false

Question 12

what is data type “factor”?

Answer 12

categorical data

Question 13

FUNCTION: levels()

Answer 13

returns categories/options from a “factor data” type object

Question 14

FUNCTION: names()

Answer 14

designed to extract the column names from a data frame
Can also be used to assign names to numeric values
ie.
cost

Question 15

R name for “data type”

Answer 15

class

Question 16

FUNCTION: table()

Answer 16

takes a vector as input and returns the frequency of each unique element in the vector

> x table(x)
x
a b c
2 3 1

Question 17

FUNCTION: to concatenate

Answer 17

c()

ie. c(a,b,c)
c(a=1,b=2,c=3)

Question 18

FUNCTION: to access a subset/column of a vector

Answer 18

VectorName[2]
##the 2 is for the second column
VectorName[c(1,3)]
VectorName[“columnname”,”columnname2”]

Question 19

When creating a vector, what indicates that a element is a string, not a variable?

Answer 19

Double quotes around the element (for strings)

Question 20

What is coercion?

Answer 20

An attempt by R to be flexible with data types

Question 21

FUNCTION: to convert variable/object to character types

Answer 21

as.character()

Question 22

FUNCTION: to convert variable/object to number types

Answer 22

as.numeric()

Question 23

What does NA mean?

Answer 23

Number missing

Can be created by R trying to coerce data

Question 24

FUNCTION: to specify a length

Answer 24

length. out=5

ie. seq(0, 100, length.out = 5)

Question 25

FUNCTION: returns the sorted indexes from a vector

Answer 25

order(x)
This is the index that puts x in order

EXAMPLE
> x  sort(x)
[1]  4 15 31 65 92
> order(x)
[1] 2 3 1 5 4
> index x[index]
[1]  4 15 31 65 92

Question 26

FUNCTION: that returns index of max/min from vector

Answer 26

which. max()

which. min()

Question 27

FUNCTION: which()

Answer 27

returns the indexes for the values which are true

Question 28

FUNCTION: match()

Answer 28

looks for entries in a vector and returns the index needed to access them

EXAMPLE
>index index
[1] 33 10 44

Question 29

FUNCTION: %in%

Answer 29

indicates whether or not an element of a first vector is in a second vector

EXAMPLE
> x y y %in% x
[1] TRUE, TRUE, FALSE

Question 30

FUNCTION: mutate()

deplyr

Answer 30

to change a table

ie.
murders

Question 31

FUNCTION: filter()

dplyr

Answer 31

filter(murders,rate <= 0.71)

Question 32

FUNCTION: %>%

dplyr

Answer 32

Passes object on left hand side as first argument (or . argument) of function on righthand side

x %>% f(y)is the same as f(x, y)y %>% f(x, ., z)is the same as f(x, y, z )

Question 33

When creating a data.frame, how do you prevent every element from being classified as a factor data type?

Answer 33

End the function with stringsAsFactors=FALSE

Question 34

FUNCTION: what function to create scatterplot

Answer 34

plot(x,y)

Question 35

FUNCTION: to create a historgram

Answer 35

hist(x,y)

Question 36

FUNCTION: to create boxplot

Answer 36

boxplot(x,y)

Question 37

General Form for “IF - ELSE” statement

Answer 37

if (boolean condition) {
  expressions
} else {
  alternative expressions
}

Question 38

FUNCTION: ifelse()

Answer 38

ifelse(if true, true, false)

Can use this replace values in a vector
ifelse(is.na(na_example), 0, na_example)

Question 39

FUNCTION: any()

Answer 39

if ANY entries are TRUE, will return TRUE

Question 40

FUNCTION: all()

Answer 40

if ALL entries are TRUE, will return TRUE

Question 41

HOW TO CREATE A FUNCTION

Answer 41

my_function_name

Question 42

FUNCTION: For loop

Answer 42

for(i in 1:5){
print(i)
}

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5

EXAMPLE:
m