Github user davies commented on a diff in the pull request:
https://github.com/apache/spark/pull/7113#discussion_r33652200
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala
---
@@ -354,6 +356,35 @@ case class Pow(left: Expression, right: Expression)
}
}
+/**
+ * Performs the inverse operation of HEX.
+ * Resulting characters are returned as a byte array.
+ */
+case class UnHex(child: Expression)
+ extends UnaryExpression with AutoCastInputTypes with Serializable {
+
+ override def expectedChildTypes: Seq[DataType] = Seq(StringType)
+
+ override def dataType: DataType = BinaryType
+
+ override def eval(input: InternalRow): Any = {
+ val num = child.eval(input)
+ if (num == null) {
+ null
+ } else {
+ unhex(num.asInstanceOf[UTF8String])
+ }
+ }
+
+ private def unhex(utf8Str: UTF8String): Array[Byte] = {
+ try {
+ new
org.apache.commons.codec.binary.Hex(StandardCharsets.UTF_8).decode(utf8Str.getBytes)
--- End diff --
The best approach is something like `decode(char[])`, but work with
`byte[]`, we need to implement `toDigit(Byte): Byte`, which return 10 for `97`
('a').
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