Spark UDF could not find implicit value for parameter num: Numeric[Nothing]

Question

I am trying to write generic add method for which can take any argument type and return result of that type

 def addExactUDF[T](x: T, y: T)(implicit num: Numeric[T]): T = {
    import num._
    x + y
  }

  def addExact(value1: Column, value2: Column, dataType: String): Column =
    dataType match {
      case "Int" => expr(s"addExactUDF(cast($value1 AS INT), cast($value2 AS INT))")
      case "Double" => expr(s"addExactUDF(cast($value1 AS DOUBLE), cast($value2 AS DOUBLE))")
    }

Now when I try to register the UDF

object FilterFunctionsUtil extends MathFunctionsNameSpace with StringFunctionsNameSpace {
  lazy val registerAsSparkUdf: UserDefinedFunction = {
    val sqlContext = SparkSessionFactory.getSparkSession(Map(), Nil).sqlContext

    sqlContext.udf.register("addExactUDF", addExactUDF _)
    sqlContext.udf.register("subtractExactUDF", subtractExactUDF _)
  }
}

It throw me error

   Error:(36, 44) could not find implicit value for parameter num: Numeric[Nothing]
        sqlContext.udf.register("addExactUDF", addExactUDF _)
Error:(36, 44) not enough arguments for method addExactUDF: (implicit num: Numeric[Nothing])Nothing.
Unspecified value parameter num.
    sqlContext.udf.register("addExactUDF", addExactUDF _)

how do I add the implicit to make this work

Balaji Reddy Balaji Reddy · Accepted Answer · 2018-11-21T08:02:49

Specify the implicit type while registering the UDF. you may need to register separate UDF for each type when required.

  import sqlContext.implicits._
  val df = sc.parallelize(Seq((1,2),(3,4))).toDF("val1","val2")

  df.createOrReplaceTempView("tempTable")
  sqlContext.cacheTable("tempTable")

  sqlContext.udf.register("addExtractIntUDF",addExtractUDF[Int] _)

  sqlContext.sql("select addExtractIntUDF(val1,val2) from temptable").show(false)

Result

+---------------------------------------------+
|UDF:addExtractIntUDF(val1,val2) |
+---------------------------------------------+
|3 |
|7 |
+--------------------------------------------+

Spark UDF could not find implicit value for parameter num: Numeric[Nothing]

1 Answers