ft_index_to_string.
ft_string_indexer(x, input_col = NULL, output_col = NULL, params = NULL)spark_tbl) coercable to a Spark DataFrame.labels
key.Other feature transformation routines: ft_binarizer,
  ft_bucketizer,
  ft_discrete_cosine_transform,
  ft_elementwise_product,
  ft_index_to_string,
  ft_one_hot_encoder,
  ft_quantile_discretizer,
  ft_sql_transformer,
  ft_vector_assembler,
  sdf_mutate