Ruby Basics

Front 1

For nerd points, answer any of the following:

Who created Ruby?

Where (in what country) was Ruby created? When?

Back 1

Who? Matz (Yukihiro Matsumoto)

Where? Japan

When? The 90s (specifically, 1994)

Front 2

What does REPL stand for?

And what does a REPL do?

Back 2

Read, Evaluate, Print, Loop

A REPL takes user input (read), evaluates it (eval), returns a result to the user (print), then asks for another input (loop).

Front 3

Ruby variables assign names to pieces of data.

A variable's name can consist of which types of characters?

Back 3

Letters, numbers or underscores.

Ruby variables must also be lowercase and have no spaces. They cannot start with a number and cannot include special characters like $, @ or &. Best practice is to use snakecase.

Examples: count, first_lesson, students_in_class

Front 4

Assign the number 5 to the variable x.

Back 4

x = 5

Front 5

What are the two basic types of numbers in Ruby?

Back 5

Integers (Fixnum) and decimals (Floats).

Front 6

What are surrounded by quotes and used to store collections of letters and numbers?

Back 6

Strings.

FYI, the shortest possible string is called the empty string: ""

Front 7

"Hello world!"

What are the index locations for the substring "Hello"?

Back 7

[0,1,2,3,4]

The characters in a string each have a position number called the index location. The first index location starts with zero.

Front 8

One common string method is .length, which counts how many characters are in a string -- does that character count include spaces?

Back 8

Yes, .length tells you how many characters are in the string, including spaces.

Front 9

Explain the difference between these two versions of .split, one of the common string methods:

.split

.split(argument)

Back 9

.split breaks up the string wherever it encounters a space (" ") character.

If you want to split on a character other than space (like a comma), you must use an argument. ex: .split(",")

Front 10

Both the common string methods .sub and .gsub can be used to replace parts of a string, like using "Find & Replace" in a word processor. How many arguments do these string methods need to be successful?

Back 10

Two. For both sub (substitute) and .gsub (global substitute) you’ll need to specify two arguments: first the substring you’re wanting to replace and second the string you want to replace it with.

ex. greeting = "Hello Everyone!"

greeting.gsub("Everyone!","Friends!")

Front 11

Define concatenate.

Cite an example of when something is concatenated in Ruby.

Back 11

con·cat·e·nate

to link (things) together in a chain or series.

Ex. string concatenation connecting strings and a variable (name):

name = "Frank"

puts "Good morning, " + name + "!"

Front 12

Define interpolate.

Cite an example of when something is interpolated in Ruby.

Back 12

in·ter·po·late

to insert (something) between fixed points.

Ex. string interpolation (which only works on double quoted strings) inserting data into a string using the interpolation marker #{}:

name = "Frank"

puts "Good morning, #{name}!"

Note: Anything inside those brackets will be converted into a string.

Front 13

Using the following variables, write a puts statement that prints "I am very very very excited for today!" -- use string interpolation with code/calculation inside the interpolation marker brackets:

modifier = "very "

mood = "excited"

Back 13

Possible answers:

puts "I am #{modifier * 3 + mood} for today!"

puts "I am #{modifier * 3}#{mood} for today!"

The snippet between the brackets is evaluated first, then the result is injected into the outer string. Note: you need a space in "very "...

Front 14

In the following code, capitalize is a ______ called on the _____ named name and assigned to the ______ named text.

text = "#{name.capitalize} has a dog."

Back 14

text = "#{name.capitalize} has a dog."

Answer: capitalize is a method called on the object named name and assigned to the variable named text.

Front 15

In the following code, center is a ______ that takes two _____.

puts text.center(50, '*')

Back 15

puts text.center(50, '*')

Answer: center is a method that takes two parameters.

Front 16

What objects start with a colon, represent names and strings, and have a value that cannot change?

Back 16

Symbols. The same Symbol object will be created for a given name or string for the duration of a program's execution, regardless of the context or meaning of that name.

ex. :name, :b, :inigo_montoya

Front 17

Write a simple loop that repeats the string "Hello, World!" five times.

Back 17

5.times do

puts "Hello, World!"

end

or

5.times{ puts "Hello, World!" }

Note: these answers are both blocks.

Front 18

In Ruby, what describes characters (either surrounded by braces or starting with do/end) that group a set of instructions together?

Back 18

Block.

Blocks are a powerful concept used frequently in Ruby. Think of them as a way of bundling up a set of instructions for use elsewhere.

Front 19

Blocks can be put between curly braces, but can also begin with the keyword _____ and end with the keyword ___.

Back 19

Blocks can begin with the keyword do and end with the keyword end. The do/end style is always acceptable.

ex. 5.times do

puts "Hello, World!"

end

Front 20

What will print to the screen if you run this code?

"this is a sentence".gsub("e"){|letter| letter.upcase}

Back 20

"this is a sentence".gsub("e"){|letter| letter.upcase}

Answer: "this is a sEntEncE"

- gsub is using the result of the block as the replacement for the original match.

Front 21

In Ruby, the most common collection of data is a number-indexed list called an _____.

Back 21

Array.

Arrays are created by putting pieces of data between square brackets ([]). They are separated by commas.

Front 22

Ruby arrays can grow and shrink. You can add an element to the end of an existing array by using what operator?

Back 22

The shovel operator (<<).

ex. meals = ["Breakfast", "Lunch", "Dinner"]

=> ["Breakfast", "Lunch", "Dinner"]

meals << "Dessert"

=> ["Breakfast", "Lunch", "Dinner", "Dessert"]

Front 23

What is the index location of "Dinner" in the following array?

["Breakfast", "Lunch", "Dinner", "Dessert"]

Back 23

Answer: 2

["Breakfast", "Lunch", "Dinner", "Dessert"]

0 1 2 3

Front 24

Which common array method returns strings in alphabetical order or numbers in ascending value order.

Back 24

Answer: .sort

The sort method will return a new array where the elements are sorted.

Front 25

Which common array method mashes elements within an array into a single string?

Back 25

Answer: .join

The join method returns a string created by converting each element of the array to a string, separated by the given separator.

ex. [ "a", "b", "c" ].join #=> "abc"

[ "a", "b", "c" ].join("-") #=> "a-b-c"

Front 26

You can ask an array if an object is present within the array by using which common array method?

Back 26

Answer: .include?

array.include?(object) returns true if the object exists within the array, false if it does not.

ex. a = [ "a", "b", "c" ]

a.include?("b") #=> true

a.include?("z") #=> false

Front 27

Explain the difference between these common array methods:

.each

.map (also called .collect)

Back 27

Both .each and .map/collect apply the values within a given block once for each element in the array. The difference is that .map/collect returns a new array.

ex. a = [ "a", "b", "c", "d" ]

a.each {|x| print x, "*" } #=> a*b*c*d*

a.collect { |x| x + "!" } #=> ["a!", "b!", "c!", "d!"]

Front 28

Explain the difference between zero and nil.

Back 28

Zero is something, it’s a number, and it’s not nothing. Nil is nothingness, something that doesn’t exist. If we create a five-element array then asked Ruby to give us the sixth element, Ruby will give us nil. There is no sixth element. It isn’t that there’s a blank in that sixth spot (""), it’s not a number 0, it’s nothingness: nil.

Front 29

A dictionary-like collection of unique keys and their values is called a ____.

Back 29

Hash.

A hash is an unordered collection where the data is organized by name into "key/value pairs".

ex. produce = {"apples" => 3, "oranges" => 1, "carrots" => 12}

puts "There are #{produce['oranges']} oranges in the fridge."

Front 30

In the following code, produce is a ____, apples is a _____ and 3 is a _____. The => is called a _____.

produce = {"apples" => 3, "oranges" => 1, "carrots" => 12}

Back 30

produce = {"apples" => 3, "oranges" => 1, "carrots" => 12}

Answer: produce is a hash, apples is a key and 3 is a value. The => is called a hashrocket.

Front 31

Instead of separating hash elements with a hashrocket, you can use symbols to simplify syntax. Simplify the following hash:

animals = {"elephant" => 9, "monkey" => 15, "sloth" => 2}

Back 31

Original hash:

animals = {"elephant" => 9, "monkey" => 15, "sloth" => 2}

Simplified hash:

animals = {elephant: 9, monkey: 15, sloth: 2}

Notice that the keys end with a colon rather than beginning with one, even though these are symbols.

Front 32

What do the following operators mean?

==

&&

||

Back 32

== is a way to question equality. It means "is the thing on the right equal to the thing on the left?" The = used alone attaches something on the left with something on the right (x = y). The == means that x and y are actually equal (x == y).

&& - and ("logical and") ex. if x && y, then z

|| - or ("logical or") ex. command = "q" || command = "quit"

Front 33

Conditional statements such as ==, > and < evaluate to _____ or _____.

Back 33

True or false.

The most common conditional operators:

== (equal)

> (greater than)

>= (greater than or equal to)

< (less than)

<= (less than or equal to)

Front 34

In conditional instructions with more than two statements, what comes between if and else?

Back 34

Answer: elsif

An if statement has one if statement (executed only if the statement is true), zero or more elsif statements (executed only if the statement is true), and zero or one else statement (executed if all other statements are false). Only one section of the if/elsif/else structure can execute. Once one block runs, that’s it.

Front 35

In Ruby, _____ are used to bundle one or more repeatable statements into a single unit of reusable code that you call by name.

Back 35

Method.

In Ruby, methods are used to bundle one or more repeatable statements into a single unit of reusable code that you call by name.

Front 36

Think of your human self in Ruby terms. You are an _____. If you're in school, you are an instance of the _____ Student. You have _____ like height, weight and eye color. When you "walk", "run", "wash dishes", and "daydream", you are calling _____ on yourself.

Back 36

You are an object. If you're in school, you are an instance of the class Student. You have attributes like height, weight and eye color. When you "walk", "run", "wash dishes", and "daydream", you are calling methods on yourself.

Front 37

In the following code, frank is the _____, Student is the _____ and new is the _____.

frank = Student.new

Back 37

In the following code, frank is the variable, Student is the class and new is the method.

frank = Student.new

variable = Class.method

Front 38

Explain what a predicate method is and how it differs from a regular method.

Back 38

Unlike a regular method, which applies an action to an object, a predicate method ends in a ? and is asking for a boolean return of true/false.

ex. def help?

command = "h" || command = "help"

end

This method asks "Has the user entered h or help?" Next steps depend on a true/false answer.

Front 39

What is the end result of the following code?

a = %w(taco burrito quesadilla tostada)

a.each { |food| puts food}

Back 39

Result:

taco
burrito
quesadilla
tostada

Front 40

There are three different ways to create a new array named "farm" that has the following values: pig, cow, chicken.

Explain/execute all three ways.

Back 40

1. make a list: farm = ["pig", "cow", "chicken"]

2. shortcut list, split on whitespace:

farm = %w(pig cow chicken)

3. individual steps with shovel operator:

farm = Array.new

farm << "pig"

farm << "cow"

farm << "chicken"

Front 41

Sometimes methods take one or more _____ that tell them how to do what they’re supposed to do. For instance, frank.introduction('Katrina') is a call for Frank to introduce himself to Katrina.

Back 41

Sometimes methods take one or more arguments.

ex. def introduction(target)

puts "Hi #{target}, I'm #{first_name}!"

end

frank.introduction('Katrina') => "Hi Katrina, I'm Frank!"

Note: frank has already been created as a new instance of Student class, first_name has been defined and frank.first_name = "Frank".

Front 42

If you called the following method, what would print to the screen?

"Frank's favorite number is #{frank.favorite_number}."

def favorite_number

5

6

7

end

Back 42

Answer: 7.

By default, a Ruby method returns the value of the last expression it evaluated. The last line of the favorite_number method is 7.

Front 43

Objects have a unique _____ and a common set of _____.

Back 43

Objects have a unique state and a common set of methods (or behaviors).

Front 44

An _____ variable exists for the life of an _____.

Back 44

An instance variable exists for the life of an object.

Front 45

A _____ is an abstract description of a category or type of thing.

Back 45

Answer: class.

A class is an abstract description of a category or type of thing. For example, if you are in school, you are an instance of the Student class. Your class defines what attributes (ex. first_name) and methods (ex. do_homework) all objects of the student type have.

Front 46

Write a small Ruby program that asks you what your name is. Have the program print out the number of characters in your name. Also have the program print out a message if your name is longer than 25 characters.

Back 46

def small_ruby_program
puts "What is your name?"
input = gets.strip
if input.length < 25
puts input.length
else
puts "Wow, kindergarten must have sucked for you!"
end
end

Front 47

When writing methods, what is the difference between arguments and parameters?

Back 47

The argument is the piece of code you actually put between the method's parentheses when you call it, and the parameter is the name you put between the method's parentheses when you define it.

Front 48

Array access: print every item in a 2D array

Back 48

array = [["ham", "swiss"], ["turkey", "cheddar"], ["roast beef", "gruyere"]]

array.each do |x|

x.each do |y|

puts y

end

end

Front 49

Array access: print every item in a 1D array

Back 49

friends = ["Milhouse", "Ralph", "Nelson", "Otto"]

friends.each { |x| puts "#{x}" }

or

friends.each { |x| puts x }

Front 50

Hash syntax

Back 50

my_hash = {

"tim" => "person",

"tim_age" => 31,

}

or

my_hash = Hash.new

my_hash["tim"] = "person"

or the new 1.9 style

my_hash = {

one: 1,

two: 2,

three: 3

}

Front 51

Hash access: print every item in a hash

Back 51

my_hash = {

"tim" => "person",

"tim_age" => 31,

}

my_hash.each { |x, y| puts x,y }

or

my_hash.each do |x,y|

puts x,y

end

Front 52

Hash access: print each key:value pair in a hash

Back 52

my_hash = {

"tim" => "person",

"tim_age" => 31,

}

my_hash.each { |x, y| puts "#{x}: #{y}" }

or

my_hash.each do |x,y|

puts "#{x} #{y}"

end

Front 53

Hash access: print each value in a hash

Back 53

lunch_order = {

"Ryan" => "wonton soup",

"Eric" => "hamburger",

}

lunch_order.each do |x,y|

puts y

end

or

lunch_order.each{|x,y| puts y}

Front 54

Method: .is_a?

Back 54

returns what the object is

Front 55

Method: .sort

Back 55

sorts ascending (1->10) (a-z)

Front 56

<==>

Back 56

combined comparison operator

Returns:

-1 if the first operand should precede the second

0 if they are equal

1 if the first operand should follow the second

1 <=>2

returns -1

a <=> b

returns -1

Front 57

use <=> and .sort to print out each item in an array in descending order

Back 57

fruits = ["orange", "apple", "banana", "pear", "grapes"]

fruits.sort! do |x,y|

y <=> x

end

Front 58

Hash: when it comes to a hash's key, what's the difference between a string and a symbol?

Back 58

Symbols make good hash keys for a few reasons:

1. They're immutable, meaning they can't be changed once they're created;
2. Only one copy of any symbol exists at a given time, so they save memory;
3. Symbol-as-keys are faster than strings-as-keys because of the above two reasons.

Front 59

Use select to filter a hash

Back 59

movie_ratings = {

memento: 3,

primer: 3.5,

the_matrix: 5,

truman_show: 4,

red_dawn: 1.5,

}

good_movies = movie_ratings.select{|movie,grade|grade > 3}

Front 60

Hash access: print out every key using a method

Hash access: print out every value using a method

Back 60

movie_ratings = {

memento: 3,

primer: 3.5,

}

movie_ratings.each_key{ |k| print k}

movie_ratings = {

memento: 3,

primer: 3.5,

}

movie_ratings.each_value{ |v| print v}

Front 61

Convert:

to symbol

to string

to integer

Back 61

symbol:

my_item.to_sym

or

my_item.intern

string:

my_item.to_str

integer:

my_item.to_i

Front 62

Hash access: delete a key/value pair

Back 62

my_hash.delete(key)

Front 63

Ternary conditional expression:

Explain the three parts

Explain the syntax

Back 63

Variables (local, @instance, @@class, $GLOBAL)

Constants (UPPER_CASE)

Keywords (def, if)

Method names

Front 64

Which command will check your .rb file for errors?

Back 64

ruby -cw myfile.rb

It's a mix of -c (check) and -w (a higher level of warning)

Front 65

Command to find where Ruby is installed

Back 65

rbconfig

Front 66

Describe implicit return

Back 66

In Ruby, a method will return the result of the last evaluated expression expression (JavaScript and Python don't).

Front 67

Syntax of a one-line if statement

Back 67

if boolean

puts x if true

and:

puts x if x %2 == 0

example:

my_array.each {|x| puts x if x%2 === 0}

Front 68

Method sytax and use:

.upto

.downto

Back 68

95.upto(100) {|x| print x, " "}

=>95, 96, 97, 98, 99, 100

"L".upto("P") {|letter| puts letter, " "}

=>L

=> M

=> N

=> O

=> P

Front 69

Method syntax and use:

.respondto

Back 69

age.respond_to?(:next)

=>true

Front 70

Concatenation operator

Back 70

<<

aka "the shovel". Can be used on both arrays and strings.

alphabet = ["a", "b", "c"]

alphabet << "d"

caption = "Tim loves"

caption << " Anne"

Front 71

Refactor:

unless n.is_a? Integer

return "n must be an integer."

end

if n <= 0

return "n must be greater than 0."

end

Back 71

return "n must be an integer." unless n.is_a? Integer

return "n must be greater than 0." if n <= 0

Front 72

Refactor:

prime = Prime.new

for num in (1..n)

prime_array.push(prime.next)

end

Back 72

prime = Prime.new

n.times {prime_array.push(prime.next)}

and

n.times {prime_array << (prime.next)}

Front 73

Methods:

.each

vs

.collect

Back 73

collect is for when you want to turn one array into another array

inject is for when you want to turn an array into a single value

[1, 2, 3].each { |x| x + 1 } #=> [1, 2, 3][1, 2, 3].collect { |x| x + 1 } #=> [2, 3, 4]

Front 74

Syntax:

Use yield in a method without a parameter using a non-predefined block

Back 74

def block_test

puts "We're in the method!"

puts "Yielding to the block..."

yield

puts "We're back in the method!"

end

block_test { puts ">>> We're in the block!" }

=> We're in the method!

=> Yielding to the block...

=> >>> We're in the block!

=> We're back in the method!

Front 75

Syntax:

Define a method with no parameter and use yield to pass a pre-defined block.

Back 75

def greeter

yield

end

phrase = Proc.new {puts "Hello there!"}

greeter(&phrase)

=> Hello there!

Front 76

Syntax:

Use yield in a method with a parameter

Back 76

def yield_name(name)

puts "A"

yield("Anne")

puts "B"

yield(name)

puts "C"

end

yield_name("Tim") {|n| puts "My name is #{n}"}

=> A

=> My name is Anne

=> B

=> My name is Tim

=> C

Front 77

Describe:

a proc

Back 77

You can think of a proc as a "saved" block: just like you can give a bit of code a name and turn it into a method, you can name a block and turn it into a proc. Procs are great for keeping your code DRY, which stands for Don't Repeat Yourself. With blocks, you have to write your code out each time you need it; with a proc, you write your code once and can use it many times!

Why bother saving our blocks as procs? There are two main advantages:

1. Procs are full-fledged objects, so they have all the powers and abilities of objects. (Blocks do not.)
2. Unlike blocks, procs can be called over and over without rewriting them. This prevents you from having to retype the contents of your block every time you need to execute a particular bit of code.

We can then pass the proc to a method that would otherwise take a block, and we don't have to rewrite the block over and over!

Front 78

Syntax:

Define a new proc and call it.

Back 78

cube = Proc.new { |x| x ** 3 }

[1, 2, 3].collect!(&cube)

=> [1, 8, 27]

[4, 5, 6].map!(&cube)

=> [64, 125, 216]

and

floats = [1.2, 3.45, 0.91, 7.727, 11.42, 482.911]

round_down = Proc.new {|x| x.floor}

ints = floats.collect(&round_down)

Front 79

Method:

.call

Back 79

Unlike blocks, we can call procs directly by using Ruby's .call method

Front 80

Syntax:

Lambda

Back 80

lambda { |param| block }

Front 81

Lambdas vs Procs

Back 81

If you're thinking that procs and lambdas look super similar, that's because they are! There are only two main differences.

First, a lambda checks the number of arguments passed to it, while a proc does not. This means that a lambda will throw an error if you pass it the wrong number of arguments, whereas a proc will ignore unexpected arguments and assignnil to any that are missing.

Second, when a lambda returns, it passes control back to the calling method; when a proc returns, it does so immediately, without going back to the calling method.

Front 82

Lambda/Proc:

Filter symbols out of an array using lamda and select

Back 82

my_array = ["raindrops", :kettles, "whiskers", :mittens, :packages]

symbol_filter = lambda {|x| x.is_a? Symbol}

symbols = my_array.select(&symbol_filter)

and

odds_n_ends = [:weezard, 42, "Trady Blix", 3, true, 19, 12.345]

check_int = lambda {|x| x.is_a? Integer}

ints = odds_n_ends.select(&check_int)

Front 83

Review:

block, proc, lambda

Back 83

1. A block is just a bit of code between do..end or {}. It's not an object on its own, but it can be passed to methods like .each or.select.
2. A proc is a saved block we can use over and over.
3. A lambda is just like a proc, only it cares about the number of arguments it gets and it returns to its calling method rather than returning immediately.

Front 84

Access REPL from Terminal

Back 84

IRB

Front 85

Difference between P, Puts and Print

Back 85

p puts and prints. p will return the evaluated code AND print to the console.

puts will return nil and print the output to the console.

print will not add spaces to the end of the outputs.

Front 86

convert something to float

Back 86

.to_f

Front 87

List the four identifiers

Back 87

Variables (local, @instance, @@class, $GLOBAL)

Constants (UPPER_CASE)

Keywords (def, if)

Method names

Front 88

Which command will check your .rb file for errors?

Back 88

ruby -cw myfile.rb

It's a mix of -c (check) and -w (a higher level of warning)

Front 89

Command to find where Ruby is installed

Back 89

rbconfig

Front 90

String-formatting methods

Back 90

center

puts("some string".center(5))

ljust (left justify - adds padding)

puts("some string".ljust(5))

rjust (right justify - adds padding)

puts("some string".rjust(5))

Front 91

method for absolute value

Back 91

.abs

Front 92

random number generator method

Back 92

rand

default: greater than or equal to 0.0 and less than 1.0

Pass an integer, like rand(5) and it will give an integer greater than or equal to 0 and less than 5 (0, 1, 2, 3, 4)

Front 93

Tip:

Every object in Ruby will evaluate to true unless it's false or nil.

Back 93

a

Front 94

Tip:

Ruby always returns the last expression in a method (implicit) unless you state where to return (explicit)

Back 94

a

Front 95

Every new object is "born" with with abilities, even if not manually given to it.

How would you check what abilities an object has?

Back 95

p object.methods.sort (wall of text)

puts object.methods.sort (one per line)

Front 96

object_id

Back 96

Every Ruby object has a unique ID

Even a number like 100.

ID is determined by what it refers to. For example:

a = Object.new

b = a

a and b have the same ID because they refer to the same object.

However:

a = "hello"

b = "hello"

a and b have different ID's because they're strings. It's like two copies of the same book.

Front 97

respond_to?

Back 97

A way to see if an object will respond to a message (eg, a method call, in this case the method 'talk'). It's a way of avoiding an error if you accidentally called a method that an object doesn't know, and gives conditional logic power as well:

obj = Object.new

if obj.respont_to? ("talk")

obj.talk

else

puts "Sorry, I don't know the 'talk' message."

end

Front 98

send

Back 98

An all-purpose way of getting a message out of an object so it doesn't have to check the object line-by-line.

def ticket.venue

puts warfield

end

def ticket.price

puts $40

end

print "What ticket info are you seeking? "

request gets.chomp

if ticket.respont_to? (request)

puts ticket.send(request)

else

puts "no such info available"

end

Front 99

Difference between a generic and a basic objet

Back 99

Object.mew (generic) comes with a lot of helpful behaviors.

BasicObject.new (basic) comes with only seven behaviors and is missing most the normal methods. Just enough for it to exist as an object, but not much more.

Front 100

What happens if you pass three arguments to a method that take one?

Back 100

error

Front 101

Define a method that takes any number of arguments

Back 101

def method(*x)

stuff

end

-->the value assigned by using * becomes an array

Front 102

Define a method that takes two or more arguments

Back 102

def method(a,b,*c)

stuff

end

* acts like a sponge. It only sops up anything leftover. So if there are non-* args after c (like d, e, f), those will evaluate before *c, leaving only what's left to the C array..Keep in mind the value of the items assigned using * become an array.

Front 103

Define a method that uses a default argument

Back 103

def method(a,b,c=1)

stuff

end

Front 104

Tip:

Most variables in Ruby do not hold immediate values. They simply contain a reference to a string object.

Note: Add a new card (or press TAB)the exception is variables bound to integers

Back 104

p56, Well Grounded Rubyst

Front 105

Name the types of objects in Ruby that are indeed stored in variables as immediate values.

Back 105

Integers (x=1_

Symbols (:this)

True, False, Nil

When you assign one of these values to a variable, the variable holds the value itself, rather than a reference to it.

Front 106

Ruby compares strings alphabetically, also known as ___________

Back 106

Lexigraphically (a,c,b,d,e,..)

It also considers uppercase to come before lowercase, so be sure to use the .downcase method on strings that are being compared.

Number characters are in normal order. For example, the strings "2" and "10". The string ten is in theory less than the string two because 1 comes before 2 (again, the character, not number)

Front 107

Array access:

Access an array at a particular index

Back 107

arr.at(x)

Front 108

Array access:

how to make it so an error is thrown if the array index is outside the bounds of the array

Back 108

fetch

arr.fetch(100) ==> "IndexError"

arr.fetch(100,"oops) ==>"oops"

Front 109

Array access:

Return the first element of an array

Return the last element of an array

Back 109

arr.first

arr.last

Front 110

Array access:

return the first n elements of an array

return the remaining elements of an array

Back 110

arr.take()

arr.drop(n)

Front 111

Array access:

check whether an array contains any elements

check if an array includes a specific element

Back 111

array.empty?

==> true/false

array.include?("Tim")

Front 112

Array access:

add an item to the end of an array

Back 112

arr.push(5)

or

arr << 5

Front 113

array access:

add an item to the beginning of an array

Back 113

arr.unshift(5)

Front 114

array access:

at an element to any position of an array

Back 114

arr.insert(n, "apple")

arr.insert(n, "apple","pear")

Front 115

array access:

remove and return the last item of an array

retrieve and remove the first item

Back 115

arr.pop

arr.shift

Front 116

array acces:

remove an element at a particular index

Back 116

arr.delete_at(n)

Front 117

array access:

remove all nil elements from an array

Back 117

arr.compact!

or

arr.compact

Front 118

array access:

remove all duplicate elements from an array

Back 118

arr.uniq!

or

arr.uniq

Front 119

array access:

loop over each item of an array

reverse loop over each item

Back 119

arr.each { |x| print x}

doesn't change the original array

arr.reverse_each {|x| print x}

Front 120

array access:

loop over each item of an array, and create a new array with the output

loop over each item of an array and update the existing array.

Back 120

arr.map {|x| 2*x}

arr.map! {|x| 2*x}

Front 121

array access:

select and return items from an array

reject and return items from an array

Do this but instead update the original array

Back 121

arr.select {|x| x<2}

arr.reject {|x| x>2}

arr.select! {|x| x<2}

Front 122

array access:

delete and return

keep and return

Back 122

arr.delete_if {|x| x<2}

arr.keep_if {|x| x>2}

*has the opposite effect of select/reject

Front 123

Array access:

lowest

highest

total

length

average

sorted

Back 123

arr.min

arr.max

arr.inject(:+)

arr.length

total.to_f / len

arr.sort

Front 124

array access:

test if an array is:

empty

nil

Back 124

arr.empty?

arr.nil?

Front 125

array access:

return the smallest number in an array

return the largest number in an array

Back 125

def smallest(someArr)

return someArr.min

end

Front 126

array access:

return the shortest string in an array

return the longest string in an array

Back 126

def shortest(someArr)

return someArr.each(|a,b| a.length <=> b.length}

end

Front 127

array access:

concatenate an array

Back 127

array1 + array2

or, as a method:

def concatenateArr(arr1,arr2)

return arr1+arr2

end

Front 128

Tip: is an array method, just like length and reverse are array methods. Methods that act like loops are called iterators Iterators are always followed by blocks.

Tip: while, end, do, if, else (and others) are not methods, they are keywords.

Tip: x.times do is an integer method. Iterators are always followed by blocks.

Back 128

a

Front 129

Loops:

What statement should you use if you don't know how many times you need to loop?

What are some examples of when you don't know how many times you need to loop?

Back 129

For example, when you flip a coin, for when you ask someone for a specific input (there's a chance they could keep entering the wrong input).

Front 130

Control flow:

What are the four control flow techniques?

Back 130

Conditional execution (based on true/false)

Looping (repeat a segment of code)

Iteration (method call is supplemented with a segment of code that the method can call on one or more times)

Exceptions (error handling)

Front 131

Control flow:

What are the three ways to write an statement?

Back 131

if condition

#some code

end

if then end

if ; ; end

Front 132

Control flow:

what keyword could you use if you wanted to write an statement that only ran if the condition was not true?

Back 132

unless

It's like saying "anything but the true/test statement"

WGR suggests avoiding unless (and simply negating an if-statement), unless you find a case where it works better.

You could instead just invert the condition (!) or you could swap places of the condition (x > 10 versus x<10)

Front 133

Array method:

reduce

Back 133

array.reduce(:+) will add each item in the array

(5..10).reduce(:+) will add each item in the range

Front 134

range

Back 134

array.each {|a..z| do something}

num = 5

array = (1..num).to_a

puts array

=>[1,2,3,4,5]

Front 135

Opposite of an if loop

Back 135

unless

Front 136

Opposite of a while loop

Back 136

until

Front 137

How can you code a while loop to ensure it always puts N at least once?

Back 137

place the while at the end, and use begin/end:

n=10

begin

puts n

end while n < 10

Front 138

Tip:

a code block is not an argument. Think of a code block as part of a method's syntax, not as it's argument.

Back 138

a

Front 139

Method blocks:

using curly braces around a block is technically not the same as do/end

Back 139

Braces almost act like parenthesis, where do/end might come too late, mainly when there's something like "puts" before. If you have puts before a do/end block, it will try to puts the method, causing an enumerator error.

OK: puts array.map {|n| n+1}

Will error: puts array.map do |n| n+1 end

It will try to puts the array.map and will ignore the do/end block.

Front 140

Arrays and hashes are examples of ____ _____

Back 140

collection objects

Front 141

Tip:

Errors raise an exception. An exception is an instance of the class Exception. All errors are descendants of this class. They're all sub-classes.jjjuujju

Back 141

a

Front 142

Error handling:

When an error happens, Ruby either deals with it or aborts. What do you need to supply if you want Ruby to handle exceptions?

Back 142

A rescue clause

Front 143

Error handling:

What is Ruby's error handling keyword for when you want to use default handling?

What is the syntax?

Back 143

rescue

Explicit: (begin/end)

begin

rescue

end

Implicit: (just end)

rescue

end

Front 144

Error handling:

What is Ruby's built in keyword for when you want to build your own exception?

Back 144

raise

Front 145

The operator is also known as ____ and is said to entice ______

Back 145

Bang

Danger

It's a receiver-changing operator.

Front 146

Tip:

Creating new objects (like when you don't use the bang operator) can be expensive as far as resources go. But using bang can also be destructive - other parts of the program might rely on the data.

Back 146

a

Front 147

Tip:

What happens if you convert an all-letter string to an integer/float?

What happens if you convert this string to an integer? "123abc"

What about the string "abc123"?

Back 147

Ruby allows it but the result is 0 or 0.0

Ruby ignores the letters, conversion is performed only on the leading digits. The result is 123 or 123.0

Ruby allows it but the result is 0 or 0.0

Front 148

What is a stricter way to convert something to integer or float?

Back 148

Use the method Float or Integer.

Yes, they are capitalized.

Front 149

Tip:

Every expression in Ruby evaluates to an object, and every object has a boolean value of true or false.

Back 149

a

Front 150

Tip:

True/fals/nil are objects themselves. That way, an expression like 1<2 can evaluate to something (the objects true/false/nil).

True/false can be looked at as both states, as well as special object.

Nil isn't an error. It's just a state (and an object), like true and false. And it's value is false.

Back 150

a

Front 151

Nil has a boolean value of _____

Back 151

false

Front 152

What does scalar mean?

Back 152

It means one-dimensional.

When used with strings, symbols, integers etc, it means items that have single values, as opposed to being a container holding multiple values (arrays, hashes, etc).

Front 153

Ruby provides two classes that handle the entirety of text representation and manipulation. They are ____ and _____.

Back 153

strings

symbols

Front 154

Strings:

difference between using single and double quotes

Back 154

Interpolation doesn't work on single-quoted strings.

Escaping (\) works differently.

Front 155

Strings:

alternative quoting mechanisms

Back 155

%char{text}

%q{text} for single quotation mark

%Q{text} for double quotation mark

Front 156

Strings:

The + method always returns a new string. How can you permanently add a string to another?

Back 156

The append method <<

Front 157

Tip:

Interpolation works with any Ruby expression, not just strings.

Back 157

"The sum is #{2+2}"

=> "The sum is 4"

Front 158

String methods:

Which method to tell you how many times a given letter (or set of letters) occurs in a string?

Which method to test if a string is blank?

Which method to test if a sting contains a specific character or word?

Which method to test if a string starts or ends with a certain character or word?

Back 158

string.count("str")

string.empty?

string.include?("str")

string.start_with?("str")

*all are case-sensitive

Front 159

String method:

.count

Back 159

string.count("str")

string.count("a-z")

string.count("^xyz")

(^ negates, so it returns the count of the letters that aren't xyz)

Front 160

String method:

.index

Back 160

Returns the index to the left of the first occurrence.

string.index("str")

You can do this from the right using

string.rindex("str")

Front 161

String method:

check the ordinal code of a string

check the string at a given ordinal code

Back 161

"a".ord

==>97

97.chr

=>"a"

Front 162

Strings:

What's the difference between string transformation and string conversion?

Back 162

Transformation involves applying some kind of algorithm or procedure to the content of a string.

Conversion means deriving a second, unrelated object - usually not even a string - from the string.

Front 163

Strings:

Method examples of transformation

Back 163

case (.upcase .downcase .swapcase .caplitalize)

format (.rjust .ljust .center .strip .lstrip .rstrip)

content (.chop .chomp .clear .replace .delete .crypt .next .succ)

Front 164

String method:

What would you use to get the next letter in the alphabet?

Back 164

.succ or .next

Front 165

String method:

what would you use to empty a string of all its contents?

what about swap all its contents for a new string?

Back 165

.clear

.replace

Front 166

Strings:

examples of string conversions

Back 166

.to_f

.to_s

.to_sym

.to_i

Front 167

What are the three main advantages of using symbols as hash keys?

Back 167

Ruby can process them fasterThey look good. They give a feeling of being frozen, non-malleable (less prone to errors)They can be written with the colon before or after the name. eg :symbol or symbol:, where the latter is nice for creating a list (eg a key/value pair)

Front 168

In what two ways are symbols similar and dislike integers?

Back 168

ImmutableUnique*because of this, they can't be "changed" like strings can, eg appending new letters.

Front 169

Name the four container types in Ruby

Back 169

Array

Hash

Range

Set

Front 170

Numbers:Numbers are objects. Describe the family tree of numberic classes.

Back 170

Numeric breaks down into floats and integers.Integers break down into fixnums and bignums

Front 171

In what ways are symbols similar to strings?

Back 171

They have a table of methods that share some similarities, like:.capitalize .upcase .empty? .length .sliceWhat's interesting is that indexing a symbol returns a substring, not a symbol. Symbols acknowledge the fact that they're representations of text.

Front 172

Numbers:What are the characteristics about dividing floats and integers?

Back 172

If you divide an integer with an integer, you'll always get an integer.You must feed floating point numbers if you want that as an output (even if it means just adding .0 to the end of the inputs)

Front 173

Arrays:

Name the four ways to create an array

Back 173

Array.new

literal constructor

Array method

%w{...} and %i{...}

Front 174

Array:

Array.new

Back 174

Array.new()

=>[]

Array.new(3)

=> [nil,nil,nil]

Array.new(3, "red")

=>['red','red','red']

*these are the same objects. To get different objects, do:

Array.new(3) { "red" }

Array.new(3) {n += 1; n*10}

=>[10,20,30]

Front 175

Array:

which array tool could you use to separate a string into an array of words ?

Back 175

%W{"tim cannady is fun"}

=>["tim","cannady","is","fun"]

use %w for single-quotes

Front 176

Array:

which tool could you used to separate a group of characters into an array of symbols?

Back 176

i%{ a b c }

=>[:a, :b, :c]

Front 177

Array:

What's the difference between << and push?

Back 177

Push can take arguments (eg, can push more than one object at a time), whereas the shovel method can only do one object at a time.

Front 178

Array:

When working with two separate arrays, what's the difference between the two methods .push and .concat?

Back 178

concat concatenates the array, whereas push will make a 3-d array

Front 179

Array:

What are some ways to join two arrays?

Back 179

array1.concat(array2)

=>combined arrays

=> array1 will be a combined array

=> array2 will be left alone

array2 = array1 + [1,2,3]

=>combined arrays

=> array2 will be a combined array

=> array1 will be left alone

Front 180

Array:

what's the difference between using .replace versus just re-assigning a new array to the variable?

Back 180

.replace keeps the same original object, where re-assigning refers a completely new one. .replace is like "keeping the original placeholder so everything around it can still work, just simply replace the value." Reassigning is like saying "forget the old object, look over here instead"

a = [1,2,3]

b = a

a.replace([4,5,6])

a

=>[4,5,6]

b

=>[4,5,6]

a = [7,8,9]

b

=>[4,5,6]

Front 181

array:

what would you use to get rid of nested arrays? And what is the default behavior?

Back 181

.flatten

Default completely flattens an array. Passing arguments removes layer by layer from the top down (deepest-nested arrays are last last)

Front 182

array:

what happens if you call .join on an array that has mixed types of object elements?

Back 182

It will return a string representation of all the elements of the array strung together.

Front 183

array:

what does passing an argument to .join do

Back 183

it places the argument between the each pair of elements

Front 184

array:

what's an alternative to the .join method?

Back 184

*

It looks like multiplication, but it's not. You're actually performing a join operation:

a = ['a','b','c']

a * "-"

=> "a-b-c"

Front 185

array:

which method will return the array with all the duplicate elements removed?

Back 185

.uniq

Front 186

array:

what would you use do get rid of all nil elements in an array?

Back 186

.compact

Front 187

array:

what's the other method like .length

Back 187

.size

Front 188

array:

what method to determine if there's elements present in an array?

Back 188

.empty?

Front 189

array:

what method to see if the array has a certain element in it?

Back 189

.include?

Front 190

array:

what method to return how many occurrences of a certain item?

Back 190

.count(item)

Front 191

array:

which method to return the first n-elements of an array?

last n-elements?

Back 191

.first(n)

.last(n)

Front 192

Hash tip:

Any key and any value can be any Ruby object

Back 192

a

Front 193

Hash:

Four ways to create a hash.

Back 193

Literal constructor

Hash.new

Hash.[] method

Top-level method whose name is Hash

Front 194

Hash:

literal constructor

Back 194

The most common technique.

Convenient when you have values you wish to hash that aren't go ing to change.

Front 195

Hash:

Hash.[] class method

Back 195

Thanks to syntatic sugar, you can put the arguments to [] directly inside the brackets and dispense them with the method-calling dot:

Hash["tim", "TC", "anne", "AN"]

=> {"tim"=>"TC","anne","AN"}

Can pass an array of arrays, too:

Hash[[1,2],[3,4],[5,6]]

=> {1=>2,3=>4,5=>6}

Front 196

Hash:

Name two was to add a key/value pair to a hash.

Back 196

Essentially the same technique as an array:

state_hash["New York"] = "NY

which is the same as:

state_hash.[] = ("New York", "NY")

Second way:

state_hash.store("New York", "NY")

Front 197

Hash:

What happens if you duplicate a key inside a hash?

Back 197

The first gets overwritten

Front 198

Hash tip:

The workhorse technique for retrieving hash values is the [] method.

Using a hash key is much like indexing an array - except that the index (the key) can be anything, whereas in an array it's always an integer.

Back 198

a

Front 199

Hash:

Name the three ways to retrieve value(s) from a hash, and explain which one throws an exception if the key is nonexistent

Back 199

california_abbrev = state_hash["California"]

=> CA

california_abbrev = state_hash.fetch("California")

=> CA

two_states = state_hash.values_at("California","Nevada")

.fetch will raise an exception, whereas [] gives either nil or a default value.

Front 200

Hash:

Name the two methods to combine hashes, describe their syntax, and describe which is/isn't destructive

Back 200

.update (destructive)

h1.update(h2)

.merge (non-destructive)

h3 = h1.merge(h2)

Front 201

Hash:

which method to choose key/value pairs based on the value?

which method to ignore?

Back 201

.select {|k,v| }

.reject {|k,v| }

Front 202

Hash:

which method could you use to remove key/value pairs?

Back 202

.delete_if { }

.keep_if { }

Front 203

Hash:

which method flips the keys/values?

Back 203

.invert

(keep in mind keys must be unique. Duplicates will be discarded)

Front 204

hash:

which method to empty a hash?

Back 204

.clear

Front 205

hash:

which method to replace a hash with something else?

Back 205

.replace({ })

Front 206

hash:

what are some methods to see if a hash has a certain key?

Back 206

.has_key?(key)

.include?(key)

.key?(key)

.member?(key)

Front 207

hash:

what are some methods to see if a hash has a certain value?

Back 207

.has_value?(value)

.value?(value)

Front 208

hash:

which method to see if a hash has no keys/values?

Back 208

.empty?

Front 209

hash:

which method to list the amount of key/value pairs in a hash?

Back 209

.size

Front 210

Range tip:

You can't use range for floating-point numbers because there is, in theory, an infinite amount of values between two whole numbers.

Only use range for integers.

Back 210

a

Front 211

Range:

What are the two ways to create a range?

What is the default of the constructor?

Back 211

r = Range.new(1,100)

default = inclusive

r = Range.new(1,100,true)

pass "true" to force exclusive

literal syntax:

r = 1..100

inclusive

r = 1...100

exclusive. Having more dots "pushes" the final number out of range.

*don't create 'backwards' ranges. The way it works is by testing if the argument is larger than the first and smaller than the second. If you reverse arrays, this logic will fail (but Ruby will allow it, so don't get confused).

Front 212

Range:

what are the two methods to test inclusion of a value in a range, and what are their differences?

Back 212

.cover?

Can test strings ("a" and "abc")

.include?

Can only test individual characters ("a"). It kind of looks at the range as a crypto-array.

(aka .member?)

*be sure to consider case-sensitivity

Front 213

Classes:

define an instance method

Back 213

It's a method defined inside of a class, intended for use by all instances of the class. The don't belong to just one object, they belong to all instances of that class.

Front 214

Classes:

what's the term for a non-instance method?

Back 214

a singleton method

Front 215

Classes:

Describe an instance variable

Back 215

Begins with @

Only visible to the object they belong

Can be used y other methods so long as they belong to/were created within the same class.

Unlike a local variable, instance variables retain the value assigned to them even after the method in which they were initialized has terminated.

Front 216

Classes:

Describe setter methods

Back 216

Setter methods are ways to assign (or reassign) values to instance variables.

There's lots of ways to do this. See WGR p70.

One of tricks: when defining a method in a class, use an equals sign after the method's name. This will let you do method calls that look like reassignments:

def price=(amount)

@price = amount

end

thedn you can call it like:

ticket.price=(63.00)

or even

ticket.price = 63.00

Front 217

Classes:

Describe an attribute

Back 217

An attribute is a property of an object w hose value can be read and/or written.

In the case of the ticket objects, we'd say that each ticket has a price attribute, as well as a date and venue attribute.

Front 218

Classes:

what tool does Ruby provide so you don't have to create repetitive setter methods within a class?

For example, so you don't have to write a bunch of read/write setter methods for each of the class' attributes?

Back 218

attr_reader :price, :venue, :band

attr_writer :price

attr_accessor: :x

Front 219

Classes:

how many classes can a Ruby object inherit from?

Back 219

Just one. Ruby uses single-inheritance

A teacher can be a person, but not also an employee

If you want to get into that, use modules.

Front 220

Classes:

describe inheritance and it's limitations

Back 220

Inheritance is defined via <

class person < human

Inheritance in Ruby is single-inheritance.

Inheritance often functions more as a convenient way to get two or more classes to share method definitions than as a definitive statement of how real-world objects relate to each other in terms of generality or specificity.

Front 221

Classes:

what's at the top of every class' inheritance tree?

Back 221

the Object and BasicObject classes

Front 222

Classes tip:

Remember, classes are objects. Instances are classes of objects. A class object (like ticket) has its own methods, its own state, and its own identity. It doesn't share these things with instances of itself. Sending a message to Ticket (the class) isn't the same as sending a message to instances of Ticket.

Back 222

a

Front 223

Classes:

Describe constants and their syntax

Back 223

Constants can be used for names of classes. They can also be used to set and preserve important data values in classes.

They begin with a capital letter, sometimes all caps.

It's possible to perform an assignment on an already-assigned constant, but you'll get a warning.

They can referred to from inside the class's instance or class methods. However it's possible to refer to them from outside the class definition by using the special constant lookup notation (::)

class Tickets

VENUES = ["a","b"]

end

puts Tickets::VENUES

Front 224

Classes:

What method to determine whether an objetc has a given class, either as its class or as one of its class's ancestral classes?

Back 224

is_a?(Class)

examples: String, Array, Person, Human

Can be more than one due to inheritance.

Front 225

Classes:

What's the difference between an instance variable and a class variable?

Back 225

Instance variable is attached to the object. It uses @. There can be one for every instance. Instance variables are available across methods for any particular instance or object.

Class variable is attached to the class. It uses @@. There's only one per class. Class variables are available across different objects. A class variable belongs to the class and is a characteristic of a class.

Front 226

Classes:

What's the difference between instance methods and class methods?

Back 226

Instance methods can access pretty much anything in the class. EG reading/writing instance methods, variables, they can read 'self'.

Class methods are less common. You call them through the class, you don't need an instance. They're defined by prefixing it with the class name or with .self

Front 227

Classes:

What do you do if you want each instance of the class to be "set up"? EG starting values for the instance variables

Back 227

initialize()

Can create custom parameters. It's called by the .new method, for example:

Person.new("Tim", 31)

Front 228

Array:

Create sub-arrays of n-length, each with their own name, from a larger array

Back 228

def groups_of_n(array)

array.each_slice(n).with_index {|group, index|

puts "Array Number #{index+1}: #{group,inspect}"

}

end

Front 229

Array:

two ways to randomize an array

Back 229

array.shuffle

or if using older versions of Ruby:

array.sort_by {rand}

Front 230

Classes:

What do you need to do if you define a class as an enumerator?

Back 230

You must define because all methods that come with enumerable are defined in terms of each.

In some respects, you might say the whole concept of a "collection" in Ruby is pegged to the enumerable modules and the methods it defines on top of

Front 231

Hashes:

How could you create an array of all a hash's keys?

What about an array of all a hash's values?

Back 231

hash.keys

kash.values

Front 232

Enumeration:

Which method would you use to return the first element in an array that met a certain circumstance?

Back 232

array.find { }

It returns nil if none are found

Front 233

Which container object is the most generic and thus the result of most method types?

Back 233

arrays

Front 234

Enumeration:

which method could you use to return element in an array that meet a certain circumstance?

Back 234

array.find_all { }

aka array.select {}

It returns an empty array if none are found.

Find_all does not have a bang version. Select does.

Front 235

Enumeration:

which method could you use to return all elements of an array that don't meet a certain circumstance?

Back 235

array.reject { }

it's the opposite of select

Front 236

Enumeration:

explain grep

Back 236

I think it basically returns anything that is equal (===) to what you passed it.

For example, if you ask it to return all elements that contain the letter o (/o/) or all elements that have whitespace (%w())

It's basically a long-winded form of select and can be thought of like this:

enumerable.select {|element| expression === element}

grep can take a block as well, so it can select all words that have the letter "o" and then do something to them, like capitalize.

Front 237

Enumeration:

explain group_by

Back 237

creates a hash where a key is created for each unique evaluated value (from the block), and the values are an array of the elements that resulted in that key.

What's cool is when you pass the block a method that outputs numbers (size, length

Front 238

Enumerable:

describe

Back 238

it returns the first thing yielded by each.

For example, the first value of an array, or the first key-value pair of a hash

Front 239

Enumerable:

which enumerable classes have a method?

Back 239

array and range

Front 240

Enumerable tip:

methods like and can't do much if your method is infinitely-yielding. This is because they don't output until the yielding is done.

Back 240

a

Front 241

Enumerable:

which methods would you use if you wanted to grab the first to elements of an array?

what if you wanted to grab everything but the first two elements of an array?

Back 241

array.take(n)

array.drop(n)

Front 242

Enumerable:

describe and

describe how you can use them to perform based on non-default criteria

Back 242

they return the value based on <=>

if you want to do this based on custom criteria, then pass a block

arry.min {|a,b| a.size <=> b.size}

a more streamlined approach to using a custom block would be to use min_by or max_by:

arry.min_by{|a| a.size}

Front 243

Enumerable:

if you call or on a hash, which will be used: the key or the value?

Back 243

the key

to do it by value, you can do this:

hash.min_by{|k,v| v}

Front 244

Enumerable:

describe:

each

each_index

each_with_index

with_index

each.with_index

Back 244

each is each

each_index returns the index

each_with_index returns the index

with_index takes a starting parameter to change the counter for the index. Note it's the counter, not the actual starting position.

Front 245

Enumerable:

what are two different ways you could iterate over characters of a string?

Back 245

.split it into an array

or

keep it as a string and use .each_char

Front 246

Enumerable tip:

strings aren't enumerable in the technical sense - String does not include Enumerable.

However Ruby provides necessary tools to traverse them either as characters, bytes, code points and/or line-by-line.

Back 246

a

Front 247

Enumerable:

If you have a class and want to be able to sort it amongst others of the same class, you need to do the following:

Back 247

define a comparison method for the class (<=>)

place the multiple instances in a container

sort the container

Front 248

Enumerable tip:

If you want to create a sortable class, you can just put the objects into a container type that already has enumerable (like array or hash). They already have sort and sort_by.

Back 248

a

Front 249

Enumerable:

what are the two ways to outline sort behavior?

Back 249

define the <=> method (p309 wgr)

or

pass sort a block (p310 wgr)

Front 250

OOP:

How many scopes are there, and describe them

Back 250

CONSTANT = 5

global scope

$global = 5

global scope

@@class = 5

exist over all instances of the class

changing the @@wheels of the Car class changes it for both the Bus car object and the SUV car object.

@instance = 5

exist over just that instance of the class

local = 5

Front 251

Modules:

why use modules over inheritance?

Back 251

Because you can mix-in more than one module, while a class can only inherit from one class.

Front 252

Modules:

Where does the Module class sit in the hierarchy when it comes to the Class class?

Back 252

Module sits above the class Class.

Kernel is a module that Object mixes in.

Object sits below BasicObject.

It's in Kernel that most of Ruby's fundamental methods objects are defined.

Every class that doesn't have an explicit superclass is a subclass of Object.

Front 253

Modules:

Objects don't "have" methods. Rather they find them by searching modules and classes.

Front 254

Modules:

explain the lookup path

Back 254

1) modules prepended to its class, in reverse order of prepending

2) its class

3) modules included in its class, in reverse order of inclusion

4) modules prepended to its superclass

5) its class's superclass

6) modules included in its superclass

7) likewise, up to Object (and its mix-in Kernel) and BasicObject

Front 255

Modules:

what's the name of the keyword to call a method from a parent class

Back 255

super

POODR suggests avoiding it

Front 256

Modules:

modules don't have instances

Back 256

It follows that entities or things are generally best modeled in classes, and characteristics or properties of entities or things are best encapsulated in modules.

EG: classes are typically nouns, and modules are typically adjectives (stack vs stacklike)

Front 257

What is an interesting characteristic of For-loops in Ruby?

Back 257

The iterator is accessible after the loop is complete.

arr = [1, 2, 3]

# badfor elem in arr do puts elemend# note that elem is accessible outside of the for loop

elem

# => 3

# good

arr.each { |elem| puts elem }

# elem is not accessible outside each's blockelem

# => NameError: undefined local variable or method `elem'