How to work with arrays in Ruby

In Ruby, arrays are ordered, integer-indexed, list-like collections of any kind of an object. Array index starts from 0 in Ruby, just like in C and Java. A negative array index is assumed to be relative from the end of the array.

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Initializing arrays in Ruby

There are multiple ways to initialize arrays in Ruby as discussed below:

1. Using literal constructor

A new array can be created by using the literal constructor []. Have a look at the following array:

arr = [1, 2, 3, 4, 5]
puts "#{arr}"

2. Using new keyword

An array can also be created using new along with arguments.

  • Line 1: When no argument is given, an empty array of size 0 is created.

  • Line 3: When one integer argument is given, it is treated as size, and an empty array of that length is created.

  • Line 5: When another argument along with the integer argument is given, the array of the given length is created and filled with the second argument.

arr1 = Array.new()
puts "#{arr1}"
arr2 = Array.new(6)
puts "#{arr2}"
arr3 = Array.new(3, "Educative")
puts "#{arr3}"

3. Using a block

Arrays can also be created by using a block along with new. The array is then filled with the values produced by the block.

  • Line 1,2: This method can be used to fill the array with elements each of which depends on the element on the last index.

  • Line 3,4: Using this method, you can create multi-dimensional arrays, like the empty 4x4 array created in the example below.

arr1 = Array.new(5){|a| a = a * 3}
puts "#{arr1}"
arr2 = Array.new(4){Array.new(4)}
puts "#{arr2}"

Array access and other methods

Arrays in Ruby have many useful built-in methods.

  • at(int): Method to access an array element at the given index. Returns nil, if no element is present at the index, or the index is out of bounds.
  • fetch(int, string): Method to access an array element. Raises out of bounds error if index, which is the first argument, is out of range. Alternatively, if a second parameter is given, it gets printed.
  • length / size: Returns an integer specifying the length of the array.
  • first: Returns the first element of the array.
  • last: Returns the last element of the array.
  • take(int): Returns first n elements from the array, as specified by the passed integer.
  • drop(int): Returns last length-n elements from the array, as specified by the passed integer
  • empty?: Returns a boolean value after checking if an array contains any elements in it.
  • include?(ele): Returns a boolean specifying whether the passed ele exists in the array or not.
  • push(ele) / << ele: Adds element to the end of the array.
  • unshift(ele): Adds ele to the beginning of the array.
  • insert(int, ele ... ): Adds element(s) starting from the given integer index.
  • pop: Removes and returns the last element.
  • shift: Removes and returns the first element.
  • delete_at(int): Removes an element at the given integer index
arr1 = Array.new(10){|a| a * 3}         # Create 10 element array
puts "#{arr1}"                          # print the array
puts arr1.at(-1)                        # print element at index 1
puts arr1.fetch(5)                      # print element at index 5
puts arr1.fetch(100, "oops: OutOfRange")# print element at index 100
puts arr1.length                        # print array length
puts arr1.size                          # print array length
puts arr1.first                         # print first element of array
puts arr1.last                          # print last element of array
puts "#{arr1.take(5)}"                  # print first 5 element of array
puts "#{arr1.drop(5)}"                  # print last 5 elements of array
puts arr1.empty?                        # check if array is empty
puts arr1.include?(9)                   # check if array includes 9
puts "#{arr1.push(100)}"                # add 100 to the end of array
puts "#{arr1 << 100}"                   # add 100 to the end of array
puts "#{arr1.unshift(-1)}"              # add -1 to the start of array
puts "#{arr1.insert(3, 4, 5)}"          # add 4 and 5 at index 3 of array
puts "#{arr1.pop}"                      # delete and return last element 
puts "#{arr1.shift}"                    # delete and return first element 
puts "#{arr1.delete_at(-1)}"            # delete and return last element
puts "#{arr1}"                          # print the final array
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