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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_subgroups(self, subgroups):
 """ Update the subgroups for this track. Note that in contrast to :meth:`CompositeTrack`, which takes a list of :class:`SubGroupDefinition` objects representing the allowed subgroups, this method takes a single dictionary indicating the particular subgroups for this track. Parameters subgroups : dict Dictionary of subgroups, e.g., {'celltype': 'K562', 'treatment': 'a'}. Each key must match a SubGroupDefinition name in the composite's subgroups list. Each value must match a key in that SubGroupDefinition.mapping dictionary. """

        if subgroups is None:
            subgroups = {}
        assert isinstance(subgroups, dict)
        self.subgroups.update(subgroups)