Define steps to process arrays in batches

step_by_step.rb

  def self.join(first, last)
    if first.is_a?(Range) && last.is_a?(Range)
      first.first..last.last
    elsif first.is_a?(Range)
      first.first..last
    elsif first == last
      first
    else
      first..last
    end
  end

  def self.define_steps(a, by)
    result = {}
    remaining = a.to_a
    while remaining.size > 1
      remaining = remaining.each_slice(by).map do |slice|
        result[slice] = join(slice.first, slice.last)
      end
    end
    result.reject! {|k| k.size == 1}
  end


a = 1..10

result = define_steps(a, 3)

expected = {[1, 2, 3] => 1..3,
            [4, 5, 6] => 4..6,
            [7, 8, 9] => 7..9,
            [1..3, 4..6, 7..9] => 1..9,
            [1..9, 10] => 1..10
}
if result == expected
  puts 'ok'
  puts result.values.last
else
  p result
  p expected
end