Ruby Array

A Ruby array is an ordered collection of objects indexed by integer keys. Each element in the array is associated with an index and can be accessed by this index.

The indexing starts at 0, similar to C or Java. Negative indices count from the end of the array, where -1 indicates the last element, -2 the second-to-last element, and so on.

Ruby arrays can store objects such as String, Integer, Fixnum, Hash, Symbol, and even other Array objects.

Ruby arrays do not require a predefined size; they automatically grow as elements are added.

Creating Arrays

There are several ways to create or initialize an array. One way is to use the new class method:

names = Array.new

You can set the size of the array when creating it:

names = Array.new(20)

The names array has a size or length of 20 elements. You can use the size or length method to return the array's size:

Example

#!/usr/bin/ruby

names = Array.new(20)
puts names.size  # Returns 20
puts names.length # Returns 20

The output of the above example is:

20
20

You can assign values to each element in the array as follows:

Example

#!/usr/bin/ruby

names = Array.new(4, "mac")

puts "#{names}"

The output of the above example is:

["mac", "mac", "mac", "mac"]

You can also use a block with new, which fills each element with the result of the block:

Example

#!/usr/bin/ruby

nums = Array.new(10) { |e| e = e * 2 }

puts "#{nums}"

The output of the above example is:

[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

Another method for creating arrays is [], as shown below:

nums = Array.[](1, 2, 3, 4, 5)

Another form of array creation is as follows:

nums = Array[1, 2, 3, 4, 5]

In the Ruby core module, there is an Array method that accepts a single argument, creating an array of numbers using a range as a parameter:

Example

#!/usr/bin/ruby

digits = Array(0..9)

puts "#{digits}"

The output of the above example is:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Built-in Array Methods

We need an instance of an Array object to call Array methods. Here is how to create an instance of an Array object:

Array.[](...) [or] Array[...] [or] [...]

This returns a new array filled with the given objects. Now, using the created object, we can call any available method. For example:

Example

#!/usr/bin/ruby

digits = Array(0..9)

num = digits.at(6)

puts "#{num}"

The output of the above example is:

6

Below are the public array methods (assuming array is an Array object):

Array Pack Directives

The following table lists pack directives for the Array#pack method.

Example

Try the following example to pack various data.

a = [ "a", "b", "c" ]
n = [ 65, 66, 67 ]
puts a.pack("A3A3A3")   #=> "a  b  c  "
puts a.pack("a3a3a3")   #=> "a\000\000b\000\000c\000\000"
puts n.pack("ccc")      #=> "ABC"

Output:

a  b  c
abc
ABC