Github user ueshin commented on a diff in the pull request:
https://github.com/apache/spark/pull/21053#discussion_r181623803
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
---
@@ -287,3 +287,106 @@ case class ArrayContains(left: Expression, right:
Expression)
override def prettyName: String = "array_contains"
}
+
+/**
+ * Returns the value of index `right` in Array `left` or the value for key
`right` in Map `left`.
+ */
+@ExpressionDescription(
+ usage = """
+ _FUNC_(array, index) - Returns element of array at given index. If
index < 0, accesses elements
+ from the last to the first.
+
+ _FUNC_(map, key) - Returns value for given key, or NULL if the key is
not contained in the map
+ """,
+ examples = """
+ Examples:
+ > SELECT _FUNC_(array(1, 2, 3), 2);
+ 2
+ > SELECT _FUNC_(map(1, 'a', 2, 'b'), 2);
+ "b"
+ """,
+ since = "2.4.0")
+case class ElementAt(left: Expression, right: Expression) extends
GetMapValueUtil {
+
+ override def dataType: DataType = left.dataType match {
+ case _: ArrayType => left.dataType.asInstanceOf[ArrayType].elementType
+ case _: MapType => left.dataType.asInstanceOf[MapType].valueType
+ }
+
+ override def inputTypes: Seq[AbstractDataType] = {
+ Seq(TypeCollection(ArrayType, MapType),
+ left.dataType match {
+ case _: ArrayType => IntegerType
+ case _: MapType => left.dataType.asInstanceOf[MapType].keyType
+ }
+ )
+ }
+
+ override def nullable: Boolean = true
--- End diff --
I'm afraid it's wrong because this returns `null` when the given index is
"out of bounds" (`array.numElements() < math.abs(index)`) for array type or the
given key doesn't exist for map type.
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