code: def unmask(self, arr):
          
          self._check_for_mask()
  
          if 1 > arr.ndim > 2:
              raise ValueError('The given array has {} dimensions while my mask has {}. '
                               'Masked data must be 1D or 2D array. '.format(arr.ndim,
                                                                             len(self.mask.shape)))
  
          if arr.ndim == 2:
              return matrix_to_4dvolume(arr, self.mask.get_data())
          elif arr.ndim == 1:
              return vector_to_volume(arr, self.mask.get_data())
docs: Use self.mask to reshape arr and self.img to get an affine and header to create
          a new self.img using the data in arr.
          If self.has_mask() is False, will return the same arr.