yhuang-db commented on code in PR #51308: URL: https://github.com/apache/spark/pull/51308#discussion_r2201358589
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/ApproxTopKExpressions.scala: ########## @@ -0,0 +1,114 @@ +/* + * 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 + +import org.apache.datasketches.frequencies.ItemsSketch +import org.apache.datasketches.memory.Memory + +import org.apache.spark.sql.catalyst.InternalRow +import org.apache.spark.sql.catalyst.analysis.FunctionRegistry +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.aggregate.ApproxTopK +import org.apache.spark.sql.catalyst.expressions.codegen.CodegenFallback +import org.apache.spark.sql.types._ + +/** + * An expression that estimates the top K items from a sketch. + * + * The input is a sketch state that is generated by the ApproxTopKAccumulation function. + * The output is an array of structs, each containing a frequent item and its estimated frequency. + * The items are sorted by their estimated frequency in descending order. + * + * @param state The sketch state, which is a struct containing the serialized sketch data, + * the original data type and the max items tracked of the sketch. + * @param k The number of top items to estimate. + */ +// scalastyle:off line.size.limit +@ExpressionDescription( + usage = """ + _FUNC_(state, k) - Returns top k items with their frequency. + `k` An optional INTEGER literal greater than 0. If k is not specified, it defaults to 5. + """, + examples = """ + Examples: + > SELECT _FUNC_(approx_top_k_accumulate(expr)) FROM VALUES (0), (0), (1), (1), (2), (3), (4), (4) AS tab(expr); + [{"item":0,"count":2},{"item":4,"count":2},{"item":1,"count":2},{"item":2,"count":1},{"item":3,"count":1}] + + > SELECT _FUNC_(approx_top_k_accumulate(expr), 2) FROM VALUES 'a', 'b', 'c', 'c', 'c', 'c', 'd', 'd' tab(expr); + [{"item":"c","count":4},{"item":"d","count":2}] + """, + group = "misc_funcs", + since = "4.1.0") +// scalastyle:on line.size.limit +case class ApproxTopKEstimate(state: Expression, k: Expression) + extends BinaryExpression + with CodegenFallback + with ImplicitCastInputTypes { + + def this(child: Expression, topK: Int) = this(child, Literal(topK)) + + def this(child: Expression) = this(child, Literal(ApproxTopK.DEFAULT_K)) + + private lazy val itemDataType: DataType = { + // itemDataType is the type of the "ItemTypeNull" field of the output of ACCUMULATE or COMBINE + state.dataType.asInstanceOf[StructType]("ItemTypeNull").dataType + } + + override def left: Expression = state + + override def right: Expression = k + + override def inputTypes: Seq[AbstractDataType] = Seq(StructType, IntegerType) + + override def checkInputDataTypes(): TypeCheckResult = { + val defaultCheck = super.checkInputDataTypes() + if (defaultCheck.isFailure) { + defaultCheck + } else if (!k.foldable) { + TypeCheckFailure("K must be a constant literal") + } else { Review Comment: Added in https://github.com/apache/spark/pull/51308/files#diff-6fefa9db05fd13cba298c3e28d85bdb0fca70a3141b64d9fecf3ebc489386257R475 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
