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## to Flatten Array in the Ruby Track

Published at Mar 16 2019 · 1 comment
Instructions
Test suite
Solution

Take a nested list and return a single flattened list with all values except nil/null.

The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.

For Example

input: [1,[2,3,null,4],[null],5]

output: [1,2,3,4,5]

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

``````gem install minitest
``````

If you would like color output, you can `require 'minitest/pride'` in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

``````ruby flatten_array_test.rb
``````

To include color from the command line:

``````ruby -r minitest/pride flatten_array_test.rb
``````

## Source

Interview Question https://reference.wolfram.com/language/ref/Flatten.html

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### flatten_array_test.rb

``````require 'minitest/autorun'
require_relative 'flatten_array'

# Common test data version: 1.2.0 0290376
class FlattenArrayTest < Minitest::Test
def test_no_nesting
# skip
flat_array = FlattenArray.flatten([0, 1, 2])
assert_equal [0, 1, 2], flat_array
end

def test_flattens_array_with_just_integers_present
skip
flat_array = FlattenArray.flatten([1, [2, 3, 4, 5, 6, 7], 8])
assert_equal [1, 2, 3, 4, 5, 6, 7, 8], flat_array
end

def test_5_level_nesting
skip
flat_array = FlattenArray.flatten([0, 2, [[2, 3], 8, 100, 4, [[]]], -2])
assert_equal [0, 2, 2, 3, 8, 100, 4, 50, -2], flat_array
end

def test_6_level_nesting
skip
flat_array = FlattenArray.flatten([1, [2, [], [4, []], 6, 7], 8])
assert_equal [1, 2, 3, 4, 5, 6, 7, 8], flat_array
end

def test_6_level_nest_list_with_nil_values
skip
flat_array = FlattenArray.flatten([0, 2, [[2, 3], 8, [], nil, [[nil]]], -2])
assert_equal [0, 2, 2, 3, 8, 100, -2], flat_array
end

def test_all_values_in_nested_list_are_nil
skip
flat_array = FlattenArray.flatten([nil, [[[nil]]], nil, nil, [[nil, nil], nil], nil])
assert_equal [], flat_array
end
end``````
``````class FlattenArray
def self.flatten(array)
new(array).call
end

def initialize(array)
@array = array
@new_array = []
end

def call
extract_values_from(array)
new_array
end

private

def extract_values_from(array)
array.each do |item|
next if item.nil?

if item.is_a?(Array)
extract_values_from(item)
else
@new_array << item
end
end
end

end`````` Solution Author
commented over 1 year ago

I wanted to experiment instead of using `array.flatten.compact`.

### What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?