docs: def transformer(self):
          """
          Creates the internal transformer that maps the cluster center's high
          dimensional space to its two dimensional space.
          """
          ttype = self.embedding.lower() # transformer method type
  
          if ttype == 'mds':
              return MDS(n_components=2, random_state=self.random_state)
  
          if ttype == 'tsne':
              return TSNE(n_components=2, random_state=self.random_state)
  
          raise YellowbrickValueError("unknown embedding '{}'".format(ttype))