Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/21802#discussion_r205483672 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/RandomIndicesGenerator.scala --- @@ -0,0 +1,45 @@ +/* + * 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.util + +import org.apache.commons.math3.random.MersenneTwister + +/** + * This class is used to generate a random indices of given length. + * + * This implementation uses the "inside-out" version of Fisher-Yates algorithm. + * Reference: + * https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#The_%22inside-out%22_algorithm + */ +case class RandomIndicesGenerator(randomSeed: Long) { + private val random = new MersenneTwister(randomSeed) + + def getNextIndices(length: Int): Array[Int] = { --- End diff -- it should take a `Array[Int]`, to save the array creation.
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