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remcopeereboom's solution

to Flatten Array in the Ruby Track

Published at Aug 17 2018 · 0 comments
Test suite


This exercise has changed since this solution was written.

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 exercism help 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


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.


require 'minitest/autorun'
require_relative 'flatten_array'

# Common test data version: 1.1.0 d7a3c09
class FlattenArrayTest < Minitest::Test
  def test_no_nesting
    # skip
    fa = FlattenArray.flatten([0, 1, 2])
    assert_equal [0, 1, 2], fa

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

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

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

  def test_6_level_nest_list_with_null_values
    fa = FlattenArray.flatten([0, 2, [[2, 3], 8, [[100]], nil, [[nil]]], -2])
    assert_equal [0, 2, 2, 3, 8, 100, -2], fa

  def test_all_values_in_nested_list_are_null
    fa = FlattenArray.flatten([nil, [[[nil]]], nil, nil, [[nil, nil], nil], nil])
    assert_equal [], fa

  # Problems in exercism evolve over time, as we find better ways to ask
  # questions.
  # The version number refers to the version of the problem you solved,
  # not your solution.
  # Define a constant named VERSION inside of the top level BookKeeping
  # module, which may be placed near the end of your file.
  # In your file, it will look like this:
  # module BookKeeping
  #   VERSION = 1 # Where the version number matches the one in the test.
  # end
  # If you are curious, read more about constants on RubyDoc:
  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

  def test_bookkeeping
    assert_equal 1, BookKeeping::VERSION
# FlattenArray
# Namespace for the .flatten method.
module FlattenArray
  # Recursively flattens and compacts the array.
  # @param array [Array]
  # @return [Array] A new array.
  def self.flatten(array)
    acc = []

    array.each do |x|
      case x
      when Array then acc += flatten(x)
      when nil then acc
      else acc << x


# BookKeeping for exercism test versions.
module BookKeeping
  VERSION = 1 # Test version

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