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lujanfernaud's solution

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, [[[50]]]], -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, [[3]], [4, [[5]]], 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, [[100]], 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

  attr_reader :array, :new_array
end

Community comments

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Avatar of lujanfernaud

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.

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