nodes: 0, module; 1, function_definition; 2, function_name:filter_composite_from_subgroups; 3, parameters; 4, block; 5, identifier:s; 6, expression_statement; 7, expression_statement; 8, for_statement; 9, if_statement; 10, comment:"""
      Given a sorted list of subgroups, return a string appropriate to provide as
      the a composite track's `filterComposite` argument
  
      >>> import trackhub
      >>> trackhub.helpers.filter_composite_from_subgroups(['cell', 'ab', 'lab', 'knockdown'])
      'dimA dimB'
  
      Parameters
      ----------
      s : list
          A list representing the ordered subgroups, ideally the same list
          provided to `dimensions_from_subgroups`. The values are not actually
          used, just the number of items.
      """; 11, assignment; 12, pattern_list; 13, call; 14, block; 15, identifier:dims; 16, block; 17, identifier:dims; 18, list; 19, identifier:letter; 20, identifier:sg; 21, identifier:zip; 22, argument_list; 23, expression_statement; 24, return_statement; 25, string; 26, subscript; 27, call; 28, call; 29, string_content:ABCDEFGHIJKLMNOPQRSTUVWZ; 30, identifier:s; 31, slice; 32, attribute; 33, argument_list; 34, attribute; 35, argument_list; 36, integer:2; 37, identifier:dims; 38, identifier:append; 39, call; 40, string; 41, identifier:join; 42, identifier:dims; 43, attribute; 44, argument_list; 45, string_content:; 46, string; 47, identifier:format; 48, identifier:letter; 49, string_content:dim{0}
code: def filter_composite_from_subgroups(s):
      """
      Given a sorted list of subgroups, return a string appropriate to provide as
      the a composite track's `filterComposite` argument
  
      >>> import trackhub
      >>> trackhub.helpers.filter_composite_from_subgroups(['cell', 'ab', 'lab', 'knockdown'])
      'dimA dimB'
  
      Parameters
      ----------
      s : list
          A list representing the ordered subgroups, ideally the same list
          provided to `dimensions_from_subgroups`. The values are not actually
          used, just the number of items.
      """
      dims = []
      for letter, sg in zip('ABCDEFGHIJKLMNOPQRSTUVWZ', s[2:]):
          dims.append('dim{0}'.format(letter))
      if dims:
          return ' '.join(dims)