build or check hash

def create_enrollments_hash(district, year, percentage)
  build_or_check_hash(enrollments, district, year)
  unless percentage == nil
    enrollments[district][type][year] = percentage
  end
end

def build_or_check_hash(a_hash, *some_keys)
  temp_hash = a_hash
  some_keys.each do |key|
    temp_hash[key] = {} if temp_hash.nil?
    temp_hash = temp_hash[key]
  end
end