R Lecture Week2

Question 1

What are R objects

Answer 1

we are almost never dealing with a single peice of data, single number, word etc.
we are usually dealing with collections of things
R Objects are the way to combine our individual data in larger structures. The following are all types of R Objects
Arrays
Matrix
Data Frames

Question 2

What is a Variable
how to create a variable

Answer 2

Named Values which can change
it allows you to define a value once and reuse it multiple times
3 things are needed when creating a variable
- Variable Name
- Value
- Assignment (arrow)
variable name (- arrow) value

Question 3

which makes good variable name

Answer 3

num_classes
num_students
instructor
(informative but succinct)

Question 4

What are the major Data Types to be aware of and their class

Answer 4

class(Numeric)

Double (real number with decimals) or Integer (whole numbers[uses less data])

class(character)

character (“text numbers characters”)

class( logical)

Logical/boolean data ( 5 > 6 FALSE) only true or false. as an option

Complex ( imaginary numbers sqrt(-1)). need to use 1i to be sqrt(-1)

Raw

Special Values: NULL, NA, Inf, NaN ( 0/0 = NaN not a number)
NA not avalible, NULL empty

Question 5

create a character 52 and assign it the name example_chr

check its class

change the data type from a character to integer

(explicit coercion)

Answer 5

Question 6

how to convert between the data types

Answer 6

as. character
as. logical
as. numeric

Question 7

what is implicit coercion and give an example

Answer 7

R assigning a value it can to perform the operation

takes the boolean TRUE to be 1 as its used in a numerical operation

Question 8

What are Operators and what are the types of operators

Answer 8

Numeric: * / + - %%

very strict must do math with numbers

“hello” * 5 error(non-numeric argument to binary operator)

Relational: ==, , =>

less strict can compare characters/numeric

“abc” > “xyz” FALSE “hello”> “goodbye” TRUE compare alphabetical order. Logical output (T/F)

Boolean: &, |

Other

Question 9

what is the difference

& |

Answer 9

& requires both conditions are met

requires one or the other to be met

Question 10

how to prompt a message and user input

Answer 10

readline(prompt = “ask something”)

remember if you were asking for a number it will be saved as a word, we need to use
as.numeric(variable)
to save convert into a number

Question 11

how to glue together a seres of vectors and words into an output response

Answer 11

print(paste(variable, “miles is equal to”, variable, “kilometres”))

paste is doing implicite conversion as it converts everything to characters

Question 12

how can you clean up the variables in the global environment window

Answer 12

use the broom

Question 13

what is a vector

Answer 13

collection of one or more elements of the SAME data type

collection: characters, numbers, trues/false but must be all the same data type

make one using , combine c

c(15, 20, 100, 50)

if you mix data types when making a vector R will implicitly force the data to be characters or number

Question 14

create a number vector with the numbers 15, 20, 25, -5, 102
create a character vector with hello, everyone, !

Answer 14

Question 15

how do you access a vector

Answer 15

with square brackets []

Question 16

bring up 1st, 3rd, 5th value

Answer 16

my_vector[c(1, 3, 5)]

Question 17

what is a data frame

Answer 17

in short a collection of vectors

Question 18

what are Factors

Answer 18

vectors with order

Question 19

what are arrays and matrix

Answer 19

vectors with dimensions

Question 20

##Write a program that takes a vector of the numbers 1 to 200 in a variable 
##called numbers and prints out a vector that replaces the numbers with values
##of TRUE or FALSE depending upon whether the numbers are even or not. The 
## modulus operator %% may be helpful here.

there are 2 ways

Answer 20

Question 21

Explain Factors

Answer 21

allows you to order character variables in a way that is not just alphabetical.

“large” > “medium” > “small” > “very small”

Question 22

create a vector called size,
give the characters, small, med, large

turn it into a factor

specify the levels of the factor

Answer 22

Question 23

what is a list

Answer 23

collection of elements of potentially different data types

(can be arrays, matrix, lists in lists even)

Question 24

how to look at data in a list

Answer 24

double square brackets.

(part_list [[ 1] ] ) [6:7]

takes the first chunk of data of the object grabs from 6 to 7 in that

Question 25

how to generate random numbers, say 5 random numbers between 1 and 10

Answer 25

sample(1:10, 5)

Question 26

if extracting data from a list what is the difference between
example[1]
example[[1]]

Answer 26

example[1] #gives list back with only first element
example[[1]] #Extracts first element directly

Question 27

what is a matrix

Answer 27

just like a vector except you have rows and columns (2 dimensions)

it has data of all the one type

the fact it only allows for 1 data type leads itself to maths applications more so than bis data sets

Question 28

make a matrix with 8 rows and 40 pieces of data

Answer 28

Question 29

what is an array

Answer 29

similar to a matrix buy now we have 3 dimensions not 2

Question 30

what is a data frame

Answer 30

what we more commonly use,

it has rows and columns

within each column = same data type

each column can be a new data type

Question 31

what is an object an how can you look into the structure or class of an object

Answer 31

object is the overaching name given to:

• vectors (1)
• data frames (1)
• matrix
• arrays
• lists (2)
• factors (3)

to look into the structure/class of an object:
str or class
str(my\_list)

Question 32

how to calculate the average

Answer 32

mean( vector)

summary(vector) then look at data

Question 33

how to see repeated values in a data frame or vector only once

Answer 33

unique( vector), distinct( vector)

Question 34

how to see the data set in excel type view

Answer 34

view( vector)

Question 35

how to findout how many rows are in a data set

Answer 35

nrow( vector)

Question 36

what are 3 ways to find flights called AA in a data set
1hr 25min

Answer 36

Question 37

how to check if you have NA in your data

Answer 37

anyNA(vector)

Question 38

calculate mean with NA in results

Answer 38

mean( vector, na.rm =TRUE)

Question 39

how can you view the data sets in a package

Answer 39

data(package = “package name”)

Question 40

sort into numerical or alphabetic order

Answer 40

sort( vector