# File lib/csv.rb, line 985
  def self.filter(*args)
    # parse options for input, output, or both
    in_options, out_options = Hash.new, {:row_sep => $INPUT_RECORD_SEPARATOR}
    if args.last.is_a? Hash
      args.pop.each do |key, value|
        case key.to_s
        when /\Ain(?:put)?_(.+)\Z/
          in_options[$1.to_sym] = value
        when /\Aout(?:put)?_(.+)\Z/
          out_options[$1.to_sym] = value
        else
          in_options[key]  = value
          out_options[key] = value
        end
      end
    end
    # build input and output wrappers
    input  = new(args.shift || ARGF,    in_options)
    output = new(args.shift || $stdout, out_options)
    
    # read, yield, write
    input.each do |row|
      yield row
      output << row
    end
  end