freeCodeCamp/guide/english/ruby/common-array-methods/index.md

---
title: Common Array Methods
---
## Common Array Methods

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).

For the purpose of this guide, our array will be as follows:

``` ruby
array = [0, 1, 2, 3, 4]
```

#### .length
The .length method tallies the number of elements in the array and returns the count:

``` ruby
array.length
=> 5
```
This is also similar to .count and .size methods.

``` ruby
array.count
=> 5

array.size
=> 5
```

#### .first
The .first method returns the first element of the array, the element at index 0:

``` ruby
array.first
=> 0
```

#### .last
The .last method returns the last element of the array:

``` ruby
array.last
=> 4
```

#### .take
The .take method returns the first n elements of the array:

``` ruby
array.take(3)
=> [0, 1, 2]
```

#### .drop
The .drop method returns the elements after n elements of the array:

``` ruby
array.drop(3)
=> [3, 4]
```

#### array index
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:

```ruby
array[2]
=> 2

array[5]
=> nil
```

#### .pop
The .pop method will permanently remove the last element of an array and return this element:

``` ruby
array.pop
=> [0, 1, 2, 3]
```

#### .shift
The .shift method will permanently remove the first element of an array and return this element:

``` ruby
array.shift
=> 0  
array
=> [1, 2, 3, 4]
```

#### .push
The .push method will add an element to the end of an array:

``` ruby
array.push(99)
=> [0, 1, 2, 3, 4, 99]
```

#### .unshift
The .unshift method adds an element to the beginning of an array:

```
array = [2, 3]
array.unshift(1)
=> [1, 2, 3]
```

#### .delete
The .delete method removes a specified element from an array permanently:

``` ruby
array.delete(1)
=> [0, 2, 3, 4]
```

#### .delete_at
The .delete_at method permanently removes an element of an array at a specified index:

``` ruby
array.delete_at(0)
=> [1, 2, 3, 4]
```

#### .reverse
The .reverse method reverses the array but does not mutate it (the original array stays as is):

``` ruby
array.reverse
=> [4, 3, 2, 1, 0]
```

#### .select
The .select method iterates over an array and returns a new array that includes any items that return true to the expression provided.

``` ruby
array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
array.select { |number| number > 4 }
=> [5, 6, 7, 8, 9, 10]
```

#### .include?
The include? method checks to see if the argument given is included in the array and returns `true` if it is:

``` ruby
array = [1, 2, 3, 4, 5]
=> [1, 2, 3, 4, 5]
array.include?(3)
=> true
```

#### .flatten
The flatten method can be used to take an array that contains nested arrays and create a one-dimensional array:

``` ruby
array = [1, 2, [3, 4, 5], [6, 7]]
array.flatten
=> [1, 2, 3, 4, 5, 6, 7]
```

#### .join
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.

``` ruby
array.join
=> "1234"
array.join("*")
=> "1*2*3*4"
```

#### .each
The .each method iterates over each element of the array, allowing you to perform actions on them.

``` ruby
array.each do |element|
  puts element
end
=> 
0
1
2
3
4
```

#### .map
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.

``` ruby
array.map { |element| element * 2 }
  puts element
end
=> 
0
2
4
6
8
```

#### .uniq
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.

``` ruby
array = [1, 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8]
array.uniq
=> [1, 2, 3, 4, 5, 6, 7, 8]
```

#### .concat
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.
``` ruby
array = [0, 1, 2, 3, 4]
array.concat([5, 6, 7], [8, 9, 10])
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
```

#### .clear
The .clear method will delete all the data in the array:

``` ruby
array.clear
=> []
```


## More Information
* [Ruby Array docs](http://ruby-doc.org/core-2.5.1/Array.html)