Spark註冊UDF函式，用於DataFrame DSL or SQL

import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.functions._

object Test2 {
  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder()
      .appName("Spark SQL basic example")
      .config("spark.some.config.option", "some-value")
      .getOrCreate()

    // For implicit conversions like converting RDDs to DataFrames
    import spark.implicits._

    val df = Seq(("id1", 1, 100), ("id2", 4, 300), ("id3", 5, 800)).toDF("id", "value", "cnt")
    df.printSchema()

    // 註冊自定義UDF函式
    spark.udf.register("simpleUDF", (v: Int, w: Int) => v * v + w * w)

    df.select($"id", callUDF("simpleUDF", $"value", $"cnt")).toDF("id", "value").show

  }
}