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