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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 _roll_data(self):
 """ Roll window worth of data up to position zero. Save the effort of having to expensively roll at each iteration """


        self.buffer.values[:, :self._window, :] = \
            self.buffer.values[:, -self._window:, :]
        self.date_buf[:self._window] = self.date_buf[-self._window:]
        self._pos = self._window