Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/15637#discussion_r85645925
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/MapAggregate.scala
---
@@ -0,0 +1,324 @@
+/*
+ * 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 for a column returns bins - (distinct value,
frequency) pairs
+ * of equi-width histogram when the number of distinct values is less than
or equal to the
+ * specified maximum number of bins. Otherwise, it returns an empty map.
+ *
+ * @param child child expression that can produce column value with
`child.eval(inputRow)`
+ * @param numBinsExpression The maximum number of bins.
+ */
+@ExpressionDescription(
+ usage =
+ """
+ _FUNC_(col, numBins) - Returns bins - (distinct value, frequency)
pairs of equi-width
+ histogram when the number of distinct values is less than or equal
to the specified
+ maximum number of bins. Otherwise, it returns an empty map.
+ """)
+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) {
+ TypeCheckFailure(
+ "The maximum number of bins provided must be a positive integer
literal >= 2 " +
+ s"(current value = $numBins)")
+ } else {
+ TypeCheckSuccess
+ }
+ }
+
+ override def update(buffer: MapDigest, input: InternalRow): Unit = {
+ if (buffer.invalid) {
+ return
+ }
+ val evaluated = child.eval(input)
+ if (evaluated != null) {
+ buffer.update(child.dataType, evaluated, numBins)
+ }
+ }
+
+ override def merge(buffer: MapDigest, other: MapDigest): Unit = {
+ if (buffer.invalid) return
+ if (other.invalid) {
+ buffer.invalid = true
+ buffer.clear()
+ return
+ }
+ buffer.merge(other, numBins)
+ }
+
+ override def eval(buffer: MapDigest): Any = {
+ if (buffer.invalid) {
+ // 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: _*)
+ }
+ ArrayBasedMapData(sorted.keys.toArray, sorted.values.toArray)
+ }
+ }
+
+ override def serialize(buffer: MapDigest): Array[Byte] = {
+ buffer match {
+ case stringDigest: StringMapDigest =>
StringMapDigest.serialize(stringDigest)
+ case numericDigest: NumericMapDigest =>
NumericMapDigest.serialize(numericDigest)
+ }
+ }
+
+ override def deserialize(bytes: Array[Byte]): MapDigest = {
+ child.dataType match {
+ case StringType => StringMapDigest.deserialize(bytes)
+ case _ => NumericMapDigest.deserialize(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 = false
+
+ 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 invalid: Boolean = false
--- End diff --
`invalid` is confusing. How about `isInvalid`?
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