School domain model

school_class.rb

class School
  attr_accessor :roster, :name, :grade
  
  def initialize(name)
    @name = name
    @roster = {}
  end

  def add_student(student_name, grade)
    @roster[grade] ||= []
    @roster[grade] << student_name
  end

  def grade(grade)
    @roster.select { |g, student_hash| return student_hash if g == grade}
  end

  def sort
    sorted_hash = {}
    self.roster.sort.each do |grade_array|
        sorted_hash[grade_array[0]] = grade_array[1].sort
    end
    sorted_hash
  end   
end