code: def get_precision(self):
          
          assert self.classifier is not None, 'not calibrated'
          arr = np.zeros((self._som.nrows, self._som.ncols))
          for ij, (lbl, p) in self.classifier.items():
              arr[ij] = p
          return arr
docs: \
          :returns: the ratio part of the dominant label for each unit.
          :rtype: 2D :class:`numpy.ndarray`