def _roll_data(self):

        self.buffer.values[:, :self._window, :] = \
            self.buffer.values[:, -self._window:, :]
        self.date_buf[:self._window] = self.date_buf[-self._window:]
        self._pos = self._window
Roll window worth of data up to position zero.
dataset/ETHPy150Open quantopian/zipline/zipline/utils/data.py/RollingPanel._roll_data