code: def transform(self, X):
          
          return _transform_selected(
              X, self._transform,
              self.categorical_features,
              copy=True
          )
docs: Transform X using one-hot encoding.
  
          Parameters
          ----------
          X : array-like or sparse matrix, shape=(n_samples, n_features)
              Dense array or sparse matrix.
  
          Returns
          -------
          X_out : sparse matrix if sparse=True else a 2-d array, dtype=int
              Transformed input.