Find out what the mean string is from a yaml document of strings (for a ... particular definition of "mean string")

mean-string.rb

require 'set'

# Calculates the mean string
class MeanString
  def initialize(strings)
    @strings = strings
  end

  def mean
    (0...average_string_length)
      .to_a
      .map(&method(:mean_character))
      .join
  end

  private

  attr_reader :strings

  def average_string_length
    @average_string_length ||=
      (strings.map(&:length).sum.to_f / strings.count)
      .round
  end

  def mean_character(idx)
    char_indices = strings_with_length_at_least(idx + 1)
                   .map { |a| a[idx] }
                   .map { |c| all_chars.index(c) }

    mean_char_index = (indices.sum.to_f / indices.count).round
    all_chars[mean_char_index]
  end

  def strings_with_length_at_least(len)
    strings.reject { |a| a.length < len }
  end

  # constructs a set of all possible characters - this allows us to use a "mean"
  # and get a value that's actually inside the possible characters, and
  # minimises the chances of getting a non-alphanumeric
  def all_chars
    @all_chars ||= Set.new(strings.map { |x| x.split('') }.flatten).sort
  end
end

require 'yaml'

# the yaml doc should be a simple array of strings, e.g.:
# - string1
# - string2
strings = YAML.safe_load(IO.read('strings.yml'))

puts MeanString.new(strings).mean