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 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:
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
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 end def test_flattens_array_with_just_integers_present skip fa = FlattenArray.flatten([1, [2, 3, 4, 5, 6, 7], 8]) assert_equal [1, 2, 3, 4, 5, 6, 7, 8], fa end def test_5_level_nesting skip fa = FlattenArray.flatten([0, 2, [[2, 3], 8, 100, 4, [[]]], -2]) assert_equal [0, 2, 2, 3, 8, 100, 4, 50, -2], fa end def test_6_level_nesting skip fa = FlattenArray.flatten([1, [2, [], [4, []], 6, 7], 8]) assert_equal [1, 2, 3, 4, 5, 6, 7, 8], fa end def test_6_level_nest_list_with_null_values skip fa = FlattenArray.flatten([0, 2, [[2, 3], 8, [], nil, [[nil]]], -2]) assert_equal [0, 2, 2, 3, 8, 100, -2], fa end def test_all_values_in_nested_list_are_null skip fa = FlattenArray.flatten([nil, [[[nil]]], nil, nil, [[nil, nil], nil], nil]) assert_equal , fa end # 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 skip assert_equal 1, BookKeeping::VERSION end end
# 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 end end acc end end # BookKeeping for exercism test versions. module BookKeeping VERSION = 1 # Test version end
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.