def id_a_to_s id_a
      id_a.map do |el|
         proc_ids = process_ids(el)
         proc_ids
      end.compact.join(",")
    end
def id_a_to_s id_a
      id_a.map do |el|
         proc_ids = process_ids(el)
         proc_ids
      end.compact.join(",")
    end
Filters should be a list of values
 Ranges interpreted as ids
 1...5 : "1,2,3,4,5"
 1..5  : "1,2,3,4"
 1     : "1"
 and joined with ","
 [1...5, 8, 9] : "1,2,3,4,5,8,9"

 @param id_a [Array<String, Range, Fixnum>]
 @return [String]
 @api public