# 
#  Overview
Flattening a Multi-dimensional array means transforming it into a one-dimensional array. The method used to arrive at this is the **`flatten!`** method. 

However, `flatten!` will not modify the original array or the array that calls the function. It will only return the expected one-dimensional array. 

> With `flatten!` the original array is changed permanently.
# 
#  Syntax
```ruby
array.flatten!
```
# 
## Parameters
This method doesn’t take any parameters.
##
## Return value
The value returned is a new one-dimensional array.
##
## Code sample
In the code below, we shall demonstrate the use of the `flatten!` method. We created some multi-dimensional arrays and flattened them permanently.

# create arrays
arr1 = [1, 2, [3, 4]]
arr2 = [[1, 2, 3,], [4, 5, 6]]
arr3 = ["a","b",["a", "b", ["a", "b"]]]

# print original arrays
puts "#{arr1}"
puts "#{arr2}"
puts "#{arr3}"

# flatten the arrays
a = arr1.flatten!
b = arr2.flatten!
c = arr3.flatten!

# print out returned values
puts "#{a}"
puts "#{b}"
puts "#{c}"



As seen above, the original arrays were changed.

How to permanently flatten a multidimensional array in Ruby

To permanently flatten a multidimensional array in Ruby, use the `flatten!` method.