def _purge_fields(cls, collection_name, field_names):
        """Removes the fields from all in-memory frames in the collection."""
        if collection_name not in cls._instances:
            return

        for frames in cls._instances[collection_name].values():
            for frame in frames.values():
                for field_name in field_names:
                    frame._doc._data.pop(field_name, None)
Removes the fields from all in-memory frames in the collection.
fiftyone/core/singletons.py