Add method to_ranges to Array Class

Array_to_ranges

# Add the function to_ranges to Array
# This funciton reduces an Array of Integer [0,1,2,3,5,8,9,10,20] to
# an Array of ranges, arrays, or fixnums
# @params [Symbol] type The result can be an Array of Arrays, Ranges,
#   or an Array with compact, sorted and uniq Fixnums
# @example
#   [0,1,2,3,5,8,9,10,20].to_ranges #=> [[0, 3], [5, 5], [8, 10], [20, 20]]
#   [0,1,2,3,5,8,9,10,20].to_ranges(:array) #=> [[0, 3], [5, 5], [8, 10], [20, 20]]
#   [0,1,2,3,5,8,9,10,20].to_ranges(:range) #=> [0..3, 5..5, 8..10, 20..20]
#   [0,1,2,3,5,8,9,10,20].to_ranges(:other) #=> [0, 1, 2, 3, 5, 8, 9, 10, 20]
class Array
  def to_ranges(type = :array)
    compact.sort.uniq.inject([]) do |r,x|
      if type == :array
        r.empty? || r.last.last.succ != x ? r << [x,x] : r[0..-2] << [r.last.first,x]
      elsif type == :range
        r.empty? || r.last.last.succ != x ? r << (x..x) : r[0..-2] << (r.last.first..x)
      else
        r << x
      end
    end
  end
end