Ruby Intro - Enumerables

Question 1

What 2 methods create new arrays?

Answer 1

map or collect do

Question 2

What’s the key difference between Map and Each?

Answer 2

Neither change the original array, however, map creates a new array while each doesn’t change anything but rather just runs through the enumerator. Map is used for it’s new array created. Each is used for the side effects of the enumeration process.

Question 3

What 2 methods creates new arrays upon True result?

Answer 3

Select or Find_all do

nums.select do |i|
i % 3 == 0

Question 4

What method tallies up total elements in array or hash?

Answer 4

count (for hashes, it counts total pairs)

num.count

Question 5

What method returns true if an element exists in a collection?

Answer 5

include?(parameter)

Question 6

What 3 methods boolean test for any element true/false in a given collection?

Answer 6

any? do
all? do
none? do

nums.any? do |i|
i % 2 == 0

Question 7

example of Super elegant way to create an array with a method being done on each element?

Answer 7

(-10..-1).map(&:abs)

Question 8

How do you use each_with_index? example

Answer 8

my_favorite_number = 42
numbers = [42, 3, 42, 5]

favorite_indices = []
numbers.each_with_index do |number, index|
  if number == my_favorite_number
    favorite_indices << index
  end
end

Question 9

What is the rule when using “i” as iterator/index in a loop?

Answer 9

i should start == 0, not 1.

Question 10

the times do function starts at what number?

Answer 10

if 5.times do, it will iterate 0, 1, 2, 3, 4