[SPARK-23939][SQL] Add transform_keys function

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala

@@ -445,6 +445,7 @@ object FunctionRegistry {
     expression[MapFilter]("map_filter"),
     expression[ArrayFilter]("filter"),
     expression[ArrayAggregate]("aggregate"),
+    expression[TransformKeys]("transform_keys"),
     CreateStruct.registryEntry,
 
     // misc functions

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/higherOrderFunctions.scala

@@ -442,3 +442,65 @@ case class ArrayAggregate(
 
   override def prettyName: String = "aggregate"
 }
+
+/**
+ * Transform Keys for every entry of the map by applying the transform_keys function.
+ * Returns map with transformed key entries
+ */
+@ExpressionDescription(
+  usage = "_FUNC_(expr, func) - Transforms elements in a map using the function.",
+  examples = """
+    Examples:
+      > SELECT _FUNC_(map(array(1, 2, 3), array(1, 2, 3), (k, v) -> k + 1);
+       map(array(2, 3, 4), array(1, 2, 3))
+      > SELECT _FUNC_(map(array(1, 2, 3), array(1, 2, 3), (k, v) -> k + v);
+       map(array(2, 4, 6), array(1, 2, 3))
+  """,
+  since = "2.4.0")
+case class TransformKeys(
+    input: Expression,
+    function: Expression)
+  extends MapBasedSimpleHigherOrderFunction with CodegenFallback {
+
+  override def nullable: Boolean = input.nullable
+
+  override def dataType: DataType = {
+    val map = input.dataType.asInstanceOf[MapType]
+    MapType(function.dataType, map.valueType, map.valueContainsNull)
+  }
+
+  override def inputTypes: Seq[AbstractDataType] = Seq(MapType, expectingFunctionType)
+
+  @transient val (keyType, valueType, valueContainsNull) =
+    HigherOrderFunction.mapKeyValueArgumentType(input.dataType)
+
+  override def bind(f: (Expression, Seq[(DataType, Boolean)]) => LambdaFunction): TransformKeys = {
+    copy(function = f(function, (keyType, false) :: (valueType, valueContainsNull) :: Nil))
+  }
+
+  @transient lazy val (keyVar, valueVar) = {
+    val LambdaFunction(
+    _, (keyVar: NamedLambdaVariable) :: (valueVar: NamedLambdaVariable) :: Nil, _) = function
+    (keyVar, valueVar)
+  }
+
+  override def nullSafeEval(inputRow: InternalRow, value: Any): Any = {
+    val map = value.asInstanceOf[MapData]
+    val f = functionForEval
+    val resultKeys = new GenericArrayData(new Array[Any](map.numElements))
+    var i = 0
+    while (i < map.numElements) {
+      keyVar.value.set(map.keyArray().get(i, keyVar.dataType))
+      valueVar.value.set(map.valueArray().get(i, valueVar.dataType))
+      val result = f.eval(inputRow)
+      if (result ==  null) {
+        throw new RuntimeException("Cannot use null as map key!")
+      }
+      resultKeys.update(i, result)
+      i += 1
+    }
+    new ArrayBasedMapData(resultKeys, map.valueArray())
+  }
+
+  override def prettyName: String = "transform_keys"
+}

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/HigherOrderFunctionsSuite.scala

@@ -59,6 +59,12 @@ class HigherOrderFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper
     ArrayFilter(expr, createLambda(at.elementType, at.containsNull, f))
   }
 
+  def transformKeys(expr: Expression, f: (Expression, Expression) => Expression): Expression = {
+    val valueType = expr.dataType.asInstanceOf[MapType].valueType
+    val keyType = expr.dataType.asInstanceOf[MapType].keyType
+    TransformKeys(expr, createLambda(keyType, false, valueType, true, f))
+  }
+
   def aggregate(
       expr: Expression,
       zero: Expression,
@@ -230,4 +236,56 @@ class HigherOrderFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper
         (acc, array) => coalesce(aggregate(array, acc, (acc, elem) => acc + elem), acc)),
       15)
   }
+
+  test("TransformKeys") {
+    val ai0 = Literal.create(
+      Map(1 -> 1, 2 -> 2, 3 -> 3),
+      MapType(IntegerType, IntegerType))
+    val ai1 = Literal.create(
+      Map.empty[Int, Int],
+      MapType(IntegerType, IntegerType))
+    val ai2 = Literal.create(
+      Map(1 -> 1, 2 -> null, 3 -> 3),
+      MapType(IntegerType, IntegerType))
+
+    val plusOne: (Expression, Expression) => Expression = (k, v) => k + 1
+    val plusValue: (Expression, Expression) => Expression = (k, v) => k + v
+
+    checkEvaluation(transformKeys(ai0, plusOne), Map(2 -> 1, 3 -> 2, 4 -> 3))
+    checkEvaluation(transformKeys(ai0, plusValue), Map(2 -> 1, 4 -> 2, 6 -> 3))
+    checkEvaluation(
+      transformKeys(transformKeys(ai0, plusOne), plusValue), Map(3 -> 1, 5 -> 2, 7 -> 3))
+    checkEvaluation(transformKeys(ai1, plusOne), Map.empty[Int, Int])
+    checkEvaluation(transformKeys(ai1, plusOne), Map.empty[Int, Int])
+    checkEvaluation(
+      transformKeys(transformKeys(ai1, plusOne), plusValue), Map.empty[Int, Int])
+    checkEvaluation(transformKeys(ai2, plusOne), Map(2 -> 1, 3 -> null, 4 -> 3))
+    checkEvaluation(
+      transformKeys(transformKeys(ai2, plusOne), plusOne), Map(3 -> 1, 4 -> null, 5 -> 3))
+
+    val as0 = Literal.create(
+      Map("a" -> "xy", "bb" -> "yz", "ccc" -> "zx"), MapType(StringType, StringType))
+    val as1 = Literal.create(
+      Map("a" -> "xy", "bb" -> "yz", "ccc" -> null), MapType(StringType, StringType))
+    val asn = Literal.create(Map.empty[StringType, StringType], MapType(StringType, StringType))
+
+    val concatValue: (Expression, Expression) => Expression = (k, v) => Concat(Seq(k, v))
+    val convertKeyToKeyLength: (Expression, Expression) => Expression =
+      (k, v) => Length(k) + 1
+
+    checkEvaluation(
+      transformKeys(as0, concatValue), Map("axy" -> "xy", "bbyz" -> "yz", "ccczx" -> "zx"))
+    checkEvaluation(
+      transformKeys(transformKeys(as0, concatValue), concatValue),
+      Map("axyxy" -> "xy", "bbyzyz" -> "yz", "ccczxzx" -> "zx"))
+    checkEvaluation(transformKeys(asn, concatValue), Map.empty[String, String])
+    checkEvaluation(
+      transformKeys(transformKeys(asn, concatValue), convertKeyToKeyLength),
+      Map.empty[Int, String])
+    checkEvaluation(transformKeys(as0, convertKeyToKeyLength),
+      Map(2 -> "xy", 3 -> "yz", 4 -> "zx"))
+    checkEvaluation(transformKeys(as1, convertKeyToKeyLength),
+      Map(2 -> "xy", 3 -> "yz", 4 -> null))
+    checkEvaluation(transformKeys(asn, convertKeyToKeyLength), Map.empty[Int, String])
+  }
 }

sql/core/src/test/resources/sql-tests/inputs/higher-order-functions.sql

@@ -45,3 +45,17 @@ select transform(zs, z -> aggregate(z, 1, (acc, val) -> acc * val * size(z))) as
 
 -- Aggregate a null array
 select aggregate(cast(null as array<int>), 0, (a, y) -> a + y + 1, a -> a + 2) as v;
+
+create or replace temporary view nested as values
+  (1, map(1,1,2,2,3,3)),
+  (2, map(4,4,5,5,6,6))
+  as t(x, ys);
+
+-- Identity Transform Keys in a map
+select transform_keys(ys, (k, v) -> k) as v from nested;
+
+-- Transform Keys in a map by adding constant
+select transform_keys(ys, (k, v) -> k + 1) as v from nested;
+
+-- Transform Keys in a map using values
+select transform_keys(ys, (k, v) -> k + v) as v from nested;

sql/core/src/test/resources/sql-tests/results/higher-order-functions.sql.out

@@ -1,5 +1,5 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 15
+-- Number of queries: 19
 
 
 -- !query 0
@@ -145,3 +145,40 @@ select aggregate(cast(null as array<int>), 0, (a, y) -> a + y + 1, a -> a + 2) a
 struct<v:int>
 -- !query 14 output
 NULL
+
+
+-- !query 15
+create or replace temporary view nested as values
+  (1, map(1,1,2,2,3,3)),
+  (2, map(4,4,5,5,6,6))
+  as t(x, ys)
+-- !query 15 schema
+struct<>
+-- !query 15 output
+
+
+-- !query 16
+select transform_keys(ys, (k, v) -> k) as v from nested
+-- !query 16 schema
+struct<v:map<int,int>>
+-- !query 16 output
+{1:1,2:2,3:3}
+{4:4,5:5,6:6}
+
+
+-- !query 17
+select transform_keys(ys, (k, v) -> k + 1) as v from nested
+-- !query 17 schema
+struct<v:map<int,int>>
+-- !query 17 output
+{2:1,3:2,4:3}
+{5:4,6:5,7:6}
+
+
+-- !query 18
+select transform_keys(ys, (k, v) -> k + v) as v from nested
+-- !query 18 schema
+struct<v:map<int,int>>
+-- !query 18 output
+{10:5,12:6,8:4}
+{2:1,4:2,6:3}