def Apply(self, trees):

    assert(type(trees) is list)
    for t in trees:
      for n in self(t):
        yield (n, t)
fast version of transform, only applicable to
dataset/ETHPy150Open spranesh/Redhawk/redhawk/common/selector.py/S.Apply--crossover with--dataset/ETHPy150Open pydata/pandas/pandas/core/groupby.py/SeriesGroupBy._transform_fast