Ruby Monstas

Arrays

Arrays are lists of things

They are the most important "collection type" in Ruby

They allow you to store many things in one variable

Examples

my_favourite_fruits = ["Banana", "Apple", "Water melon"]

monthly_expenses = [342.75, 108.20, 241.00, 632.15, 499.55]

fibonacci_numbers = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

Note: Each element in the array has the same type

Note: Elements are in a defined order

Note: Arrays can have 0 up to however many entries you want

Syntax:

[item1, item2, ...]

Empty array:

[]

Try this in IRB!

my_favourite_fruits = ["Banana", "Apple", "Water melon"]
my_favourite_fruits.length

=> 3

[].length

=> 0

Try this in IRB!

my_favourite_fruits = ["Banana", "Apple", "Water melon"]
my_favourite_fruits[1]

=> "Apple"

Syntax:

array[index]

Note: Each element in the array has a so-called index an integer denoting the position of the element in the array

Note: Indices always start at 0, so the element with index 1 is the second element

Try this in IRB!

my_favourite_fruits = ["Banana", "Apple", "Water melon"]
my_favourite_fruits[3]

=> nil

Note: If we try to access items beyond the length of the array, we get

nil

Try this in IRB!

my_favourite_fruits = ["Banana", "Apple", "Water melon"]
my_favourite_fruits.first

=> "Banana"

my_favourite_fruits.last

=> "Water melon"

Note:

.first

and

.last

are more convenient than

[0]

and

[2]

Try this in IRB!

my_favourite_fruits << "Orange"

=> ["Banana", "Apple", "Water melon", "Orange"]

Note: We can use the "shovel operator" to add elements to the end of an array

Try this in IRB!

my_favourite_fruits[2] = "Mango"

my_favourite_fruits

=> ["Banana", "Apple", "Mango", "Orange"]

Syntax:

array[index] = new_item

Try this in IRB!

my_favourite_fruits.delete("Mango")

my_favourite_fruits

=> ["Banana", "Apple", "Orange"]

Try this in IRB!

my_favourite_fruits.delete_at(2)

my_favourite_fruits

=> ["Banana", "Apple"]

What questions do you have?