[1,2,3,4,5].select { |num|  num.even?  }   #=> [2, 4]

a = %w{ a b c d e f }

a.select { |v| v =~ /[aeiou]/ }  #=> ["a", "e"]

      # TODO: 使用 MySQL 的 FIND_IN_SET，必须过滤掉逗号分割符之间的空格

      # http://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_find-in-set

      custom_subjects = SpecialSubject.where('state = ? AND pid != ? ' , 1, '').select do |subject|

        pids = subject.pid.split(',')

        pids.include? pid

      end  

      custom_subjects.each  do |subject|

        if (homepage_position = subject.homepage_position.to_i) && homepage_position != 0

          result_videos[homepage_position - 1] = subject

        end

      end