Github user mgaido91 commented on a diff in the pull request:
https://github.com/apache/spark/pull/21040#discussion_r181338128
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
---
@@ -287,3 +287,101 @@ case class ArrayContains(left: Expression, right:
Expression)
override def prettyName: String = "array_contains"
}
+
+
+/**
+ * Slices an array according to the requested start index and length
+ */
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+ usage = "_FUNC_(a1, a2) - Subsets array x starting from index start (or
starting from the end if start is negative) with the specified length.",
+ examples = """
+ Examples:
+ > SELECT _FUNC_(array(1, 2, 3, 4), 2, 2);
+ [2,3]
+ > SELECT _FUNC_(array(1, 2, 3, 4), -2, 2);
+ [3,4]
+ """, since = "2.4.0")
+// scalastyle:on line.size.limit
+case class Slice(x: Expression, start: Expression, length: Expression)
+ extends TernaryExpression with ImplicitCastInputTypes {
+
+ override def dataType: DataType = x.dataType
+
+ override def inputTypes: Seq[AbstractDataType] = Seq(ArrayType,
IntegerType, IntegerType)
+
+ override def nullable: Boolean = children.exists(_.nullable)
+
+ override def foldable: Boolean = children.forall(_.foldable)
+
+ override def children: Seq[Expression] = Seq(x, start, length)
+
+ override def nullSafeEval(xVal: Any, startVal: Any, lengthVal: Any): Any
= {
+ val startInt = startVal.asInstanceOf[Int]
+ val lengthInt = lengthVal.asInstanceOf[Int]
+ val arr = xVal.asInstanceOf[ArrayData]
+ val startIndex = if (startInt == 0) {
+ throw new RuntimeException(
+ s"Unexpected value for start in function $prettyName: SQL array
indices start at 1.")
+ } else if (startInt < 0) {
+ startInt + arr.numElements()
+ } else {
+ startInt - 1
+ }
+ if (lengthInt < 0) {
+ throw new RuntimeException(s"Unexpected value for length in function
$prettyName: " +
+ s"length must be greater than or equal to 0.")
+ }
+ // this can happen if start is negative and its absolute value is
greater than the
+ // number of elements in the array
+ if (startIndex < 0) {
+ return new GenericArrayData(Array.empty[AnyRef])
+ }
+ val elementType = x.dataType.asInstanceOf[ArrayType].elementType
+ val data = arr.toArray[AnyRef](elementType)
+ new GenericArrayData(data.slice(startIndex, startIndex + lengthInt))
+ }
+
+ override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
+ val elementType = x.dataType.asInstanceOf[ArrayType].elementType
+ nullSafeCodeGen(ctx, ev, (x, start, length) => {
+ val arrayClass = classOf[GenericArrayData].getName
+ val values = ctx.freshName("values")
+ val i = ctx.freshName("i")
+ val startIdx = ctx.freshName("startIdx")
+ val resLength = ctx.freshName("resLength")
+ val defaultIntValue =
CodeGenerator.defaultValue(CodeGenerator.JAVA_INT, false)
+ s"""
+ |${CodeGenerator.JAVA_INT} $startIdx = $defaultIntValue;
+ |${CodeGenerator.JAVA_INT} $resLength = $defaultIntValue;
+ |if ($start == 0) {
+ | throw new RuntimeException("Unexpected value for start in
function $prettyName: "
+ | + "SQL array indices start at 1.");
+ |} else if ($start < 0) {
+ | $startIdx = $start + $x.numElements();
+ |} else {
+ | // arrays in SQL are 1-based instead of 0-based
+ | $startIdx = $start - 1;
+ |}
+ |if ($length < 0) {
+ | throw new RuntimeException("Unexpected value for length in
function $prettyName: "
+ | + "length must be greater than or equal to 0.");
+ |} else if ($length > $x.numElements() - $startIdx) {
+ | $resLength = $x.numElements() - $startIdx;
+ |} else {
+ | $resLength = $length;
+ |}
+ |Object[] $values;
+ |if ($startIdx < 0) {
+ | $values = new Object[0];
+ |} else {
+ | $values = new Object[$resLength];
+ | for (int $i = 0; $i < $resLength; $i ++) {
+ | $values[$i] = ${CodeGenerator.getValue(x, elementType, s"$i
+ $startIdx")};
--- End diff --
My target of coherency was the `CreateArray` operator and the code
generated in `GenerateSafeProjection`.
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