[GitHub] [spark] henrydavidge commented on a change in pull request #25666: [SPARK-28962][SQL] Provide index argument to filter lambda functions

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henrydavidge commented on a change in pull request #25666: [SPARK-28962][SQL] Provide index argument to filter lambda functions
URL: https://github.com/apache/spark/pull/25666#discussion_r330229395
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/higherOrderFunctions.scala
 ##########
 @@ -369,6 +383,9 @@ case class ArrayFilter(
     var i = 0
     while (i < arr.numElements) {
       elementVar.value.set(arr.get(i, elementVar.dataType))
+      if (indexVar.isDefined) {
 
 Review comment:
   @maropu do you have a suggestion about how to do this without implementing codegen? I tried rewriting the logic like so:
   
   ```scala
     @transient private lazy val evalFn: (InternalRow, Any) => Any = indexVar match {
       case None => (inputRow, argumentValue) =>
         val arr = argumentValue.asInstanceOf[ArrayData]
         val f = functionForEval
         val buffer = new mutable.ArrayBuffer[Any](arr.numElements)
         var i = 0
         while (i < arr.numElements) {
           elementVar.value.set(arr.get(i, elementVar.dataType))
           if (f.eval(inputRow).asInstanceOf[Boolean]) {
             buffer += elementVar.value.get
           }
           i += 1
         }
         new GenericArrayData(buffer)
   
       case Some(expr) => (inputRow, argumentValue) =>
         val arr = argumentValue.asInstanceOf[ArrayData]
         val f = functionForEval
         val buffer = new mutable.ArrayBuffer[Any](arr.numElements)
         var i = 0
         while (i < arr.numElements) {
           elementVar.value.set(arr.get(i, elementVar.dataType))
           expr.value.set(i)
           if (f.eval(inputRow).asInstanceOf[Boolean]) {
             buffer += elementVar.value.get
           }
           i += 1
         }
         new GenericArrayData(buffer)
   
     }
   
   
     override def nullSafeEval(inputRow: InternalRow, argumentValue: Any): Any = {
       evalFn(inputRow, argumentValue)
     }
   ```
   
   But from some hacky microbenchmarking this doesn't seem to be meaningfully faster and if anything is marginally slower.

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