Github user nburoojy commented on a diff in the pull request:
https://github.com/apache/spark/pull/8592#discussion_r44176861
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeExtractors.scala
---
@@ -227,6 +227,38 @@ case class GetArrayItem(child: Expression, ordinal:
Expression)
}
/**
+ * Combines two Arrays into one Array.
+ */
+case class ArrayUnion(left: Expression, right: Expression) extends
BinaryOperator {
+
+ override def inputType: AbstractDataType = ArrayType
+
+ override def symbol: String = "++"
+
+ private def inputArrType = left.dataType.asInstanceOf[ArrayType]
+ override def dataType: DataType = inputArrType
+
+ override def genCode(ctx: CodeGenContext, ev: GeneratedExpressionCode):
String = {
+ val arrayClass = classOf[GenericArrayData].getName
+ val elementType = inputArrType.elementType
+ nullSafeCodeGen(ctx, ev, (eval1, eval2) => {
+ s"""
+ final int n1 = $eval1.numElements();
+ final int n2 = $eval2.numElements();
+ final Object[] unionValues = new Object[n1 + n2];
+ for (int j = 0; j < n1; j++) {
+ unionValues[j] = ${ctx.getValue(eval1, elementType, "j")};
+ }
+ for (int j = 0; j < n2; j++) {
+ unionValues[n1 + j] = ${ctx.getValue(eval2, elementType, "j")};
+ }
+ ${ev.primitive} = new $arrayClass(unionValues);
+ """
+ })
+ }
--- End diff --
You're absolutely right; since inserting an element into an array requires
copying the entire array, the running time is `O(n^2)` in the number of
elements in the destination array. N.B.: `n` is not necessarily the number of
elements in the source data; e.g. if the user groups by `id`.
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