Arrays

Question 1

array

Answer 1

an ordered list of elements that can be of any type.

Question 2

First method

Answer 2

This finds the first element of an array. Array.first

Question 3

Last method

Answer 3

This finds the last element of an array. Array.last

Question 4

How do you reference any part of an array by its index number?

Answer 4

Array[3]

Question 5

Pop method

Answer 5

Takes the last item off an array permanently

Question 6

Push method

Answer 6

Add an item back to array permanently. Array.push or &laquo_space;aka the shovel operator

Question 7

Map method

Answer 7

Iterates over an array applying a block to each element of an array and returns a new array with those results. Array.map

Question 8

Delete_at method

Answer 8

Eliminates the value at the index of the number passed to the method. Modifies array destructively. Array.delete_at

Question 9

Delete method

Answer 9

Sometimes I will know the value I want to delete but not the index. This method permanently deletes all instances of this value from the array.

Question 10

Uniq method

Answer 10

This method iterates through an array, deletes any duplicates that exist, then returns the result as a new array. Array.uniq

Question 11

Uniq!

Answer 11

Destructive method of uniq

Question 12

Select method

Answer 12

This method iterates over an array and returns a new array that includes any items that return true to the expression provided. numbers.select { |number| number > 4 }
It does not mutate the caller.

Question 13

unshift method

Answer 13

Method that adds values to the start of the list in an array.

Question 14

to_s method

Answer 14

Used to create a string representation of an array. Ruby does this behind the scenes when you use string interpolation on an array.

irb :001 > a = [1, 2, 3]
=> [1, 2, 3]
irb :002 > “It’s as easy as #{a}”
=> “It’s as easy as [1, 2, 3]”

Question 15

include? method

Answer 15

Checks to see if the argument given is included in the array. It has a question mark in it which usually means you can expect it to return a Boolean true or false.

irb :001 > a = [1, 2, 3, 4, 5]
=> [1, 2, 3, 4, 5]
irb :002 > a.include?(3)
=> true
irb :003 > a.include?(6)
=> false

Question 16

flatten method

Answer 16

This method can be used to take an array that contains nested arrays and create a one-dimensional array. Only destructive if it includes !

irb: 001 > a = [1, 2, [3, 4, 5], [6, 7]]
=> [1, 2, [3, 4, 5], [6, 7]]
irb: 002 > a.flatten
=> [1, 2, 3, 4, 5, 6, 7]

Question 17

each_index method

Answer 17

Iterates through the array much like the each method. However, the variable represents the index number as opposed to the value at each index. It passes the index of the element into the block and you may do as you please with it.

irb: 001 > a = [1, 2, 3, 4, 5]
=> [1, 2, 3, 4, 5]
irb: 002 > a.each_index { |i| puts "This is index #{i}" }
This is index 0
This is index 1
This is index 2
This is index 3
This is index 4
=> [1, 2, 3, 4, 5]

Question 18

each _with_index method

Answer 18

Gives us the ability to manipulate both the value and the index by passing in two parameters into the block of code. The first is the value and the second is the index.

irb: 001 > a = [1, 2, 3, 4, 5]
=> [1, 2, 3, 4, 5]
irb: 002 > a.each_with_index { |val, idx| puts "#{idx+1}. #{val}" }
1. 1
2. 2
3. 3
4. 4
5. 5
=> [1, 2, 3, 4, 5]

Question 19

sort method

Answer 19

This sorts an array by integer value.
Only destructive when followed by !

irb :001 > a = [5, 3, 8, 2, 4, 1]
=> [5, 3, 8, 2, 4, 1]
irb :002 > a.sort
=> [1, 2, 3, 4, 5, 8]

Question 20

product method

Answer 20

Returns an array that is a combination of all the elements from all arrays.

irb :001 > [1, 2, 3].product([4, 5])
=> [[1, 4], [1, 5], [2, 4], [2, 5], [3, 4], [3, 5]]