可以map一下

 val session = SparkSession.builder().config(sc).getOrCreate()
    try {

      val df = session.read.json("file:\\\\\\E:/anc.json")
        .map(new MapFunction[Row, String] {
          override def call(value: Row): String = {
            value.getAs[Long]("id").toString.substring(0, 1)
          }
        }, Encoders.STRING)

      df.show()

    } finally {
      session.close()
    }