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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 _update_key(self, mask, key):
 """ Mask the value contained in the DataStore at a specified key. Parameters mask: (n,) int (n,) bool key: hashable object, in self._data """

        mask = np.asanyarray(mask)
        if key in self._data:
            self._data[key] = self._data[key][mask]