org.apache.spark.sql.catalyst.util.RandomIndicesGenerator.scala Maven / Gradle / Ivy
The newest version!
/*
* 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] = {
val indices = new Array[Int](length)
var i = 0
while (i < length) {
val j = random.nextInt(i + 1)
if (j != i) {
indices(i) = indices(j)
}
indices(j) = i
i += 1
}
indices
}
}