Github user jiangxb1987 commented on a diff in the pull request: https://github.com/apache/spark/pull/14136#discussion_r89465541 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Percentile.scala --- @@ -0,0 +1,201 @@ +/* + * 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 org.apache.spark.sql.AnalysisException +import org.apache.spark.sql.catalyst.InternalRow +import org.apache.spark.sql.catalyst.analysis.TypeCheckResult +import org.apache.spark.sql.catalyst.expressions._ +import org.apache.spark.sql.catalyst.util._ +import org.apache.spark.sql.types._ +import org.apache.spark.util.collection.OpenHashMap + +/** + * The Percentile aggregate function returns the exact percentile(s) of numeric column `expr` at + * the given percentage(s) with value range in [0.0, 1.0]. + * + * The operator is bound to the slower sort based aggregation path because the number of elements + * and their partial order cannot be determined in advance. Therefore we have to store all the + * elements in memory, and that too many elements can cause GC paused and eventually OutOfMemory + * Errors. + * + * @param child child expression that produce numeric column value with `child.eval(inputRow)` + * @param percentageExpression Expression that represents a single percentage value or an array of + * percentage values. Each percentage value must be in the range + * [0.0, 1.0]. + */ +@ExpressionDescription( + usage = + """ + _FUNC_(col, percentage) - Returns the exact percentile value of numeric column `col` at the + given percentage. The value of percentage must be between 0.0 and 1.0. + + _FUNC_(col, array(percentage1 [, percentage2]...)) - Returns the exact percentile value array + of numeric column `col` at the given percentage(s). Each value of the percentage array must + be between 0.0 and 1.0. + """) +case class Percentile( + child: Expression, + percentageExpression: Expression, + mutableAggBufferOffset: Int = 0, + inputAggBufferOffset: Int = 0) extends ImperativeAggregate { + + def this(child: Expression, percentageExpression: Expression) = { + this(child, percentageExpression, 0, 0) + } + + override def prettyName: String = "percentile" + + override def withNewMutableAggBufferOffset(newMutableAggBufferOffset: Int): ImperativeAggregate = + copy(mutableAggBufferOffset = newMutableAggBufferOffset) + + override def withNewInputAggBufferOffset(newInputAggBufferOffset: Int): ImperativeAggregate = + copy(inputAggBufferOffset = newInputAggBufferOffset) + + private var counts = new OpenHashMap[Number, Long] + + // Mark as lazy so that percentageExpression is not evaluated during tree transformation. + private lazy val (returnPercentileArray: Boolean, percentages: Seq[Number]) = + evalPercentages(percentageExpression) + + override def children: Seq[Expression] = child :: percentageExpression :: Nil + + // Returns null for empty inputs + override def nullable: Boolean = true + + override def dataType: DataType = + if (returnPercentileArray) ArrayType(DoubleType) else DoubleType + + override def inputTypes: Seq[AbstractDataType] = + Seq(NumericType, TypeCollection(NumericType, ArrayType)) --- End diff -- We can't specify the type of the array(`FractionalType`), do we want to support `DecimalType` in the array?
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