How can I achieve the following by passing a row to a udf ?

    val df1 = df.withColumn("col_Z", 

                  when($"col_x" === "a", $"col_A")

                  .when($"col_x" === "b", $"col_B")

                  .when($"col_x" === "c", $"col_C")

                  .when($"col_x" === "d", $"col_D")

                  .when($"col_x" === "e", $"col_E")

                  .when($"col_x" === "f", $"col_F")

                  .when($"col_x" === "g", $"col_G")


As I understand it, only columns can be passed as arguments to a UDF in Scala Spark.

I have taken a look at this question:

and tried to implement this udf:

    def myUDF(r:Row) = udf {


     val z : Float = r.getAs("col_x") match {

          case "a" => r.getAs("col_A")

          case "b" => r.getAs("col_B")

          case other => lit(0.0)




but I'm getting a type mismatch error:

     error: type mismatch;

     found   : String("a")

     required: Nothing

     case "a" => r.getAs("col_A")


What am I doing wrong ?

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