This lesson will give a deeper dive on how to create, manipulate, and retrieve data from arrays.
There are a few different ways to make a new array. You can use the literal constructor or the class constructor.
my_array = 
my_array = Array.new # => 
Advanced: Don't worry about the class constructor right now. We'll learn much more about this later on. We're introducing it briefly here because you may encounter this syntax if you read through other resources you might find online.
To make an array that isn't empty, you can separate each item, known as an element, by a
, ("comma") and wrap all the elements inside
 ("square brackets").
puppies = ["bulldog", "terrier", "poodle"] # => ["bulldog", "terrier", "poodle"] random_numbers = [ 2, 5, 6, 8, 30050] # => [ 2, 5, 6, 8, 30050] mixed = ["this", "array", 7, 20, "has", 45, "integers", "&", "strings", 309] # => ["this", "array", 7, 20, "has", 45, "integers", "&", "strings", 309]
It is possible to create an array that contains disparate data types. In other words, you could create an array like the one above, that stores both strings and integers. This is generally discouraged, however. It's best to keep your arrays populated with only one kind of element.
If an array is a storage container for a list of data, then we can imagine adding and removing individual items. Let's take a look at how we can add elements to an array.
The shovel method employs the "shovel" operator (
<<) and allows you to add ("shovel") items onto the end of an array:
famous_cats = ["lil' bub", "grumpy cat", "Maru"] famous_cats << "nala cat" puts famous_cats.inspect # => ["lil' bub", "grumpy cat", "Maru", "nala cat"]
.inspect method returns a string containing a human-readable representation of an object. In this case, the list of the strings held in the array.
The shovel method (
<<) is the preferred syntax for adding elements to an array, however you might see other methods used in examples online:
.push on an array with an argument will add that element to the end of the array. It has the same effect as the shovel method explained above:
famous_cats = ["lil' bub", "grumpy cat", "Maru"] famous_cats.push("nala cat") puts famous_cats.inspect # => ["lil' bub", "grumpy cat", "Maru", "nala cat"]
To add an element to the front of an array, you can call the
.unshift method on it with an argument of the element you wish to add:
famous_cats = ["lil' bub", "grumpy cat", "Maru"] famous_cats.unshift("nala cat") puts famous_cats.inspect # => ["nala cat", "lil' bub", "grumpy cat", "Maru"]
.pop on an array will remove the last item from the end of the array. The
.pop method will also supply the removed element as its return:
famous_cats = ["lil' bub", "grumpy cat", "Maru"] maru_cat = famous_cats.pop puts famous_cats.inspect # => ["lil' bub", "grumpy cat"] puts maru_cat # => Maru
.shift on an array will remove the first item from the front of the array. The
.shift method will also supply the removed element as a return:
famous_cats = ["lil' bub", "grumpy cat", "Maru"] lil_bub = famous_cats.shift puts famous_cats.inspect # => ["grumpy cat", "Maru"] puts lil_bub # => lil' bub
Note: If you want to remove items that are not at the beginning or end of an array, use the Ruby documentation to figure out how.
When you write out a list on a notepad, you typically write each item on its own line. Whether or not the list is explicitly numbered, the list has a numerology to it based on the sequence of the lines that the items are listed upon.
Just like the items in our notepad lists, elements in an array are associated with a number that represents their order. In programming, this number is called an index. While humans typically start their lists at "1", arrays begin their indexes at
0 (zero). So, the first item in an array will always be "at index
0". If we have an array of famous (fictional) cats:
famous_cats = ["Cheshire Cat", "Puss in Boots", "Garfield"]
"Cheshire Cat" is at index
0 in the array,
"Puss in Boots" is a index
"Garfield" is at index
2. Indexes will always be one less than the count.
To access one of these items in the
famous_cats array, we can type the name of the array immediately followed by the relevant index number wrapped in square brackets (
famous_cats = ["Cheshire Cat", "Puss in Boots", "Garfield"] famous_cats # => "Puss in Boots" famous_cats # => "Cheshire Cat" famous_cats # => "Garfield"
We can also access array elements by using negative index numbers. The last item of an array is considered to be stored at an index of
-1. Let's give it a shot:
famous_cats[-1] # => "Garfield"
We can also use the
#first method on an array to access the first element:
famous_cats.first # => "Cheshire Cat"
We can use the
#last method to access the last element:
famous_cats.last # => "Garfield
What happens when we try to access the element stored in an index that doesn't exist? In other words, let's say we have our
famous_cats array that contains three elements. That means that our array contains an element at indexes
2. What happens if we try to access an element at index
3? An index element that doesn't exist.
Let's take a look:
famous_cats # => nil
To discover the index number of an element within an array, we can use the
.index() method. Calling
.index() on an array with an argument inside the parentheses will return the first index number of an element matching that argument. If no elements match the argument, then this method will return
famous_cats = ["Cheshire Cat", "Puss in Boots", "Garfield"] famous_cats.index("Puss in Boots") # => 1 famous_cats.index("Maru") # => nil
This is not an operation you will perform very often. Arrays are used to store data and usually you will use the index number of an item to access it, not the other way around.