Arrays

Next to numbers, Booleans, strings, or functions, variables can contain two more things: arrays and objects. Let’s look at arrays first.

An array is a list of items in a specific order. These items can be anything (strings, numbers,…).

You create an array by placing the values between square brackets [] while separating them with commas.

For example, these arrays both contain strings:

catsToDoList = ["Nap", "Snooze", "Eat", "Siesta", "Fight with ball of string", "Knock stuff over", "Doze", "Sleep"]

toDoList = ["Bring cape to drycleaner", "Wash Batmobile", "Pick up Robin from school", "Fight crime"]

But arrays can contain any type of value—even other arrays.

numbersOfTheBeast = [6, 6, 6]
myLotteryNumbers = [1, 2, 3, 4, 5, 6]
theGarage = ["Jobs", "Wozniak", "Some friends", ["desks", "electronics", "TV screens", "soldering iron"], ["Apple I", "US$666.66"]]

You can omit the commas when putting the items on separate lines.

theGarage = [
    "Jobs"
    "Wozniak"
    "Some friends"
    [   "desks"
        "electronics"
        "TV screens"
        "soldering iron" ]
    [   "Apple I"
        "US$666.66" ]
]

You can retrieve values by their position in the array. This position is called their index and uses zero-based numbering: The first item will have index number 0. (Something common in programming languages.)

print theGarage[0]

» "Jobs"

print theGarage[1]

» "Wozniak"

print theGarage[3]

» ["desks", "electronics", "TV screens", "soldering iron"]

With this index, you can also change the value at a certain position of the array.

theGarage[0] = "Steve Jobs"

print theGarage[0]

» "Steve Jobs"

When you have an existing array…

toDoList = ["Bring cape to drycleaner", "Wash Batmobile", "Pick up Robin from school", "Fight crime"]

…you can add extra items to it afterward with push().

toDoList.push "Save Gotham", "Pick up cape from drycleaner"

print toDoList

» ["Bring cape to drycleaner", "Wash Batmobile", "Pick up Robin from school", "Fight crime", "Save Gotham", "Pick up cape from drycleaner"]

And an array’s length property lets you check how many items it contains.

print catsToDoList.length

» 8

print toDoList.length

» 6

print numbersOfTheBeast.length

» 3

print myLotteryNumbers.length

» 6

print theGarage.length

» 5   # (it contains 3 strings + 2 other arrays)