Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/15637#discussion_r86505390
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/MapAggregate.scala
---
@@ -0,0 +1,310 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.expressions.aggregate
+
+import java.nio.ByteBuffer
+
+import scala.collection.immutable.TreeMap
+import scala.collection.mutable
+
+import com.google.common.primitives.{Doubles, Ints, Longs}
+
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
+import
org.apache.spark.sql.catalyst.analysis.TypeCheckResult.{TypeCheckFailure,
TypeCheckSuccess}
+import org.apache.spark.sql.catalyst.expressions.{Expression,
ExpressionDescription}
+import org.apache.spark.sql.catalyst.util.ArrayBasedMapData
+import org.apache.spark.sql.types.{DataType, _}
+import org.apache.spark.unsafe.types.UTF8String
+
+/**
+ * The MapAggregate function Computes frequency for each distinct non-null
value of a column.
+ * It returns: 1. null if the table is empty or all values of the column
are null.
+ * 2. (distinct non-null value, frequency) pairs if the number of distinct
non-null values is
+ * less than or equal to the specified threshold.
+ * 3. an empty result if the number of distinct non-null values exceeds
that threshold.
+ *
+ * @param child child expression that can produce column value with
`child.eval(inputRow)`
+ * @param numBinsExpression The maximum number of pairs.
+ */
+@ExpressionDescription(
+ usage = """
+ _FUNC_(col, numBins) - Computes frequency for each distinct non-null
value of column `col`.
+ It returns: 1. null if the table is empty or all values of column
`col` are null.
+ 2. (distinct non-null value, frequency) pairs if the number of
distinct non-null values
+ is less than or equal to the specified threshold `numBins`.
+ 3. an empty result if the number of distinct non-null values exceeds
`numBins`.
+ """,
+ extended = """
+ Examples:
+ > SELECT map_aggregate(col, 3) FROM tbl;
+ 1. null - if `tbl` is empty or values of `col` are all nulls
+ 2. Map((10, 2), (20, 1)) - if values of `col` are (10, 20, 10)
+ 3. Map.empty - if values of `col` are (1, 2, 3, 4)
+ """)
+case class MapAggregate(
+ child: Expression,
+ numBinsExpression: Expression,
+ override val mutableAggBufferOffset: Int,
+ override val inputAggBufferOffset: Int) extends
TypedImperativeAggregate[MapDigest] {
+
+ def this(child: Expression, numBinsExpression: Expression) = {
+ this(child, numBinsExpression, 0, 0)
+ }
+
+ // Mark as lazy so that numBinsExpression is not evaluated during tree
transformation.
+ private lazy val numBins: Int =
numBinsExpression.eval().asInstanceOf[Int]
+
+ override def inputTypes: Seq[AbstractDataType] = {
+ Seq(TypeCollection(NumericType, TimestampType, DateType, StringType),
IntegerType)
+ }
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ val defaultCheck = super.checkInputDataTypes()
+ if (defaultCheck.isFailure) {
+ defaultCheck
+ } else if (!numBinsExpression.foldable) {
+ TypeCheckFailure("The maximum number of bins provided must be a
constant literal")
+ } else if (numBins < 2) {
+ val currentValue = if (numBinsExpression.eval() == null) null else
numBins
+ TypeCheckFailure(
+ "The maximum number of bins provided must be a positive integer
literal >= 2 " +
+ s"(current value = $currentValue)")
+ } else {
+ TypeCheckSuccess
+ }
+ }
+
+ override def update(buffer: MapDigest, input: InternalRow): Unit = {
+ if (!buffer.isInvalid) {
+ val evaluated = child.eval(input)
+ if (evaluated != null) buffer.update(child.dataType, evaluated,
numBins)
+ }
+ }
+
+ override def merge(buffer: MapDigest, other: MapDigest): Unit = {
+ if (!buffer.isInvalid) {
+ if (other.isInvalid) {
+ buffer.isInvalid = true
+ buffer.clear()
+ } else {
+ buffer.merge(other, numBins)
+ }
+ }
+ }
+
+ override def eval(buffer: MapDigest): Any = {
+ if (buffer.isInvalid) {
+ // return empty map
+ ArrayBasedMapData(Map.empty)
+ } else {
+ // sort the result to make it more readable
+ val sorted = buffer match {
+ case stringDigest: StringMapDigest => TreeMap[UTF8String,
Long](stringDigest.bins.toSeq: _*)
+ case numericDigest: NumericMapDigest => TreeMap[Double,
Long](numericDigest.bins.toSeq: _*)
+ }
+ if (sorted.isEmpty) {
+ // don't have non-null values
+ null
+ } else {
+ ArrayBasedMapData(sorted.keys.toArray, sorted.values.toArray)
+ }
+ }
+ }
+
+ override def serialize(buffer: MapDigest): Array[Byte] = {
+ buffer.serialize()
+ }
+
+ override def deserialize(bytes: Array[Byte]): MapDigest = {
+ MapDigest.deserialize(child.dataType, bytes)
+ }
+
+ override def createAggregationBuffer(): MapDigest = {
+ child.dataType match {
+ case StringType => StringMapDigest()
+ case _ => NumericMapDigest()
+ }
+ }
+
+ override def withNewMutableAggBufferOffset(newMutableAggBufferOffset:
Int): MapAggregate = {
+ copy(mutableAggBufferOffset = newMutableAggBufferOffset)
+ }
+
+ override def withNewInputAggBufferOffset(newInputAggBufferOffset: Int):
MapAggregate = {
+ copy(inputAggBufferOffset = newInputAggBufferOffset)
+ }
+
+ override def nullable: Boolean = true
+
+ override def dataType: DataType = {
+ child.dataType match {
+ case StringType => MapType(StringType, LongType)
+ case _ => MapType(DoubleType, LongType)
+ }
+ }
+
+ override def children: Seq[Expression] = Seq(child, numBinsExpression)
+
+ override def prettyName: String = "map_aggregate"
+}
+
+trait MapDigest {
+ // Mark this MapDigest invalid when the size of the hashmap (ndv of the
column) exceeds numBins
+ var isInvalid: Boolean
+ def update(dataType: DataType, value: Any, numBins: Int): Unit
+ def merge(otherDigest: MapDigest, numBins: Int): Unit
+ def clear(): Unit
+ def serialize(): Array[Byte]
+}
+
+abstract class MapDigestBase[T] extends MapDigest {
+ val bins: mutable.HashMap[T, Long]
+
+ // Update bins and clear it when its size exceeds numBins.
+ def updateMap(value: T, numBins: Int): Unit = {
+ mergeMap(mutable.HashMap(value -> 1L), numBins)
--- End diff --
i think you are doing this backwards by calling mergeMap in updateMap. If
anything, it should be the other way around, i.e. mergeMap has a loop that
calls updateMap. That way you will not need to create a whole new hash map for
each record, or loop over some hash map of one entry for every record.
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