By Brian Hogan and Tony Tran

An array is a data structure that represents a list of values, called elements. Arrays let you store multiple values in a single variable. In Ruby, arrays can contain any data type, including numbers, strings, and other Ruby objects. This can condense and organize your code, making it more readable and maintainable. All arrays are objects with their own methods you can call, providing a standardized way to work with datasets.

In this tutorial, you’ll create arrays, access the values they contain, add, modify, and remove elements in an array, and iterate through the elements in an array to solve more complex problems.

You’ll start by looking at how to create arrays in more detail. As an example, here is a list of various shark species. Without an array, you might store them in individual variables:

This approach is verbose and can quickly become difficult to maintain, as it’s not very flexible. Adding another shark means you’d have to add, and track, an additional variable.

If you use an array, you can simplify this data. To create an array in a Ruby program, use square brackets: ([]), and separate the values you want to store with commas:

Instead of creating three separate variables, you now have one variable that contains all three sharks. In this example, you used square brackets — [] — to create an array, and separated each entry with a comma. If you had to add an additional shark, you would add another shark to the array rather than creating and managing a new variable.

You can print out an entire array with the print statement, which will display the array’s contents:

If you want to create an array where each entry is a single word, you can use the %w{} syntax, which creates a word array:

This is equivalent to creating the array with square braces:

However, notice that the %w{} method lets you skip the quotes and the commas.

Arrays are often used to group together lists of similar data types, but in Ruby, arrays can contain any value or a mix of values. This includes other arrays. Here’s an example of an array that contains a string, a nil value, an integer, and an array of strings:

Now you’ll look at how to access data stored in arrays.

To access a specific item, or element of an array, you reference its index, or its position in the array. In Ruby, indexes start at zero. In order to retrieve the first element from your sharks array, you append the element’s index to the variable using square brackets:

The sharks array has three elements. Here is a breakdown of how each element in the sharks array is indexed.

The first element in the array is Hammerhead, which is indexed at 0. The last element is Tiger, which is indexed at 2. Counting starts with 0 in indices, which goes against the natural intuition to start counting at 1, so you’ll want to keep this in mind until it becomes natural.

Note: It might help you to think of the index as an offset, meaning the number of places from the start of the array. The first element is at the beginning, so its offset, or index, is 0. The second element is one spot away from the first entry in the array, so its offset, or index, is 1.

You can find out how many elements are in an array with the length method:

Although the indices of sharks start at 0 and go to 2, the length property returns the number of elements in the array, which is 3. It’s not concerned with the indices at all.

If you wanted to find out the index number of a specific element in an array, such as Tiger, use the index() method:

This returns the index of the first element containing that text. If an index number is not found, such as for a value that does not exist, the console will return nil:

To get the last element of an array in Ruby, use the index -1:

Ruby also provides the first and last methods to get the first and last elements without using indices:

Attempting to access an index that doesn’t exist will return nil:

Arrays can contain other arrays, which are called nested arrays. This is one way to model two-dimensional datasets in a program. Here’s an example of a nested array:

In order to access elements in a nested array, you would add another index number to correspond to the inner array. For example, to retrieve the value coral from this nested array, you’d use the following statement:

In this example, you accessed the array at position 1 of the nested_array variable, which returned the array ["coral", "reef"]. You then accessed the elements at position 0 of that array, which was "coral".

Now you’ll look at how to add elements to an array.

You have three elements in your sharks array, which are indexed from 0 to 2:

There are a few ways to add a new element. You could assign a value to the next index, which in this case would be 3:

This method is error-prone though. If you add an element and accidentally skip an index, it will create a nil element in the array.

Attempting to access the extra array element will return its value, which will be nil:

Finding the next available index in an array is error-prone and takes extra time. Avoid errors by using the push method, which adds an element to the end of an array:

You can also use the Tutorial Series: How To Code in Ruby

Ruby is a popular object-oriented programming language. You can use Ruby to write anything from simple scripts to complex web applications. Open your favorite text editor and follow these tutorials to start exploring Ruby.

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