code: def _construct(x, categories):
      
      # type: (np.ndarray, np.ndarray) -> scipy.sparse.csr_matrix
      data = np.ones(len(x))
      rows = np.arange(len(x))
      columns = x.ravel()
      return scipy.sparse.csr_matrix(
          (data, (rows, columns)), shape=(len(x), len(categories))
      )
docs: Make a sparse matrix from an encoded array.
  
      >>> construct(np.array([0, 1, 0]), np.array([0, 1])).toarray()
      array([[1., 0.],
             [0., 1.],
             [1., 0.]])