95cfa0a492
* Improve English method examples for Ruby's guide * Improve ruby common array methods examples * Minor fix in array examples
352 lines
6.3 KiB
Markdown
352 lines
6.3 KiB
Markdown
---
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title: Common Array Methods
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---
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## Common Array Methods
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Arrays are a core foundation of programming in Ruby and most languages. Arrays are so common that it is beneficial to know, and even memorize, some of their most commonly used methods. If you want to know more about Ruby Arrays, we have [an article about them](https://guide.freecodecamp.org/ruby/ruby-arrays).
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For the purpose of this guide, our array will be as follows:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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```
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#### .length
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The `.length` method tallies the number of elements in the array and returns the count:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.length
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=> 5
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```
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This is also similar to `.count` and `.size` methods.
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.count
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=> 5
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array.size
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=> 5
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```
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#### .first
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The `.first` method returns the first element of the array, the element at index 0:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.first
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=> 0
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```
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#### .last
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The `.last` method returns the last element of the array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.last
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=> 4
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```
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#### .take
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The `.take` method returns the first n elements of the array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.take(3)
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=> [0, 1, 2]
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array
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=> [0, 1, 2, 3, 4]
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```
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#### .drop
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The `.drop` method returns the elements after n elements of the array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.drop(3)
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=> [3, 4]
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array
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=> [0, 1, 2, 3, 4]
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```
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#### array index
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You can return a specific element in an array by accessing its index. If the index does not exist in the array, `nil` will be returned:
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```ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array[2]
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=> 2
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array[5]
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=> nil
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```
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#### .pop
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The `.pop` method will permanently remove the last element of an array and return this element:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.pop
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=> 4
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array
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=> [0, 1, 2, 3]
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```
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#### .shift
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The `.shift` method will permanently remove the first element of an array and return this element:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.shift
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=> 0
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array
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=> [1, 2, 3, 4]
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```
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#### .push
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The `.push` method will add an element to the end of an array and return the array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.push(99)
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=> [0, 1, 2, 3, 4, 99]
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array
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=> [0, 1, 2, 3, 4, 99]
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```
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#### .unshift
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The `.unshift` method adds an element to the beginning of an array and return the array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.unshift(99)
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=> [99, 0, 1, 2, 3, 4]
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array
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=> [99, 0, 1, 2, 3, 4]
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```
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#### .delete
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The `.delete` method removes a specified element from an array permanently and return the element:
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``` ruby
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array = [1, 2, 3, 4, 5]
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=> [1, 2, 3, 4, 5]
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array.delete(3)
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=> 3
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array
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=> [1, 2, 4, 5]
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```
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#### .delete_at
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The `.delete_at` method permanently removes an element of an array at a specified index and return the element:
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``` ruby
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array = [1, 2, 3, 4, 5]
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=> [1, 2, 3, 4, 5]
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array.delete_at(3)
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=> 3
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array
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=> [1, 2, 3, 5]
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```
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#### .reverse
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The `.reverse` method returns a new array that includes the elements of the original array but in reverse order:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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new_array = array.reverse
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=> [4, 3, 2, 1, 0]
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new_array
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=> [4, 3, 2, 1, 0]
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array
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=> [0, 1, 2, 3, 4]
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```
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#### .select
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The `.select` method iterates over an array and returns a new array that includes any items that return true to the expression provided:
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``` ruby
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array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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new_array = array.select { |number| number > 4 }
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=> [5, 6, 7, 8, 9, 10]
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new_array
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=> [5, 6, 7, 8, 9, 10]
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array
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=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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```
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#### .include?
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The `.include?` method checks to see if the argument given is included in the array and returns `true` if it is:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.include?(3)
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=> true
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array.include?(5)
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=> false
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```
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#### .flatten
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The `.flatten` method can be used to take an array that contains nested arrays and create a one-dimensional array:
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``` ruby
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array = [1, 2, [3, 4, 5], [6, 7]]
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=> [1, 2, [3, 4, 5], [6, 7]]
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new_array = array.flatten
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=> [1, 2, 3, 4, 5, 6, 7]
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new_array
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=> [1, 2, 3, 4, 5, 6, 7]
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array
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=> [1, 2, [3, 4, 5], [6, 7]]
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```
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#### .join
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The `.join` method returns a string of all the elements of the array separated by a separator parameter. If the separator parameter is nil, the method uses an empty string as a separator between strings:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.join
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=> "01234"
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array.join("*")
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=> "0*1*2*3*4"
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array
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=> [0, 1, 2, 3, 4]
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```
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#### .each
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The `.each` method iterates over each element of the array, allowing you to perform actions on them:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.each { |element| puts element }
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=>
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0
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1
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2
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3
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4
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array
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=> [0, 1, 2, 3, 4]
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```
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#### .map
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The `.map` method is the same as the `.collect` method. The `.map` and `.collect` methods iterate over each element of the array, allowing you to perform actions on them. The `.map` and `.collect` methods differ from the `.each` method in that they return an array containing the transformed elements:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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new_array = array.map { |element| element * 2 }
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=> [0, 2, 4, 6, 8]
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new_array
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=> [0, 2, 4, 6, 8]
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array
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=> [0, 1, 2, 3, 4]
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```
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#### .uniq
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The `.uniq` method returns a copy of the array containing only unique elements. Any duplicate elements are removed from the array. The original array is not modified.
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``` ruby
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array = [1, 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8]
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=> [1, 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8]
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new_array = array.uniq
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=> [1, 2, 3, 4, 5, 6, 7, 8]
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new_array
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=> [1, 2, 3, 4, 5, 6, 7, 8]
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array
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=> [1, 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8]
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```
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#### .concat
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The `.concat` method appends the elements from an array to the original array. The `.concat` method can take in multiple arrays as an argument, which will in turn append multiple arrays to the original array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.concat([5, 6, 7], [8, 9, 10])
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=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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array
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=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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```
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#### .clear
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The `.clear` method will delete all the data in the array:
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``` ruby
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array = [0, 1, 2, 3, 4]
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=> [0, 1, 2, 3, 4]
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array.clear
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=> []
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array
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=> []
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```
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## More Information
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* [Ruby Array docs](http://ruby-doc.org/core-2.5.1/Array.html)
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