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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