001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math4.legacy.stat.descriptive.rank;
018
019import org.apache.commons.math4.legacy.core.MathArrays;
020import org.apache.commons.rng.RestorableUniformRandomProvider;
021import org.apache.commons.rng.simple.RandomSource;
022
023/**
024 * A strategy of selecting random index between begin and end indices.
025 *
026 * @since 3.4
027 */
028public class RandomPivotingStrategy implements PivotingStrategy {
029    /** Source of randomness. */
030    private final RandomSource randomSource;
031    /** Random generator to use for selecting pivot. */
032    private transient RestorableUniformRandomProvider random;
033
034    /**
035     * Simple constructor.
036     *
037     * @param randomSource RNG to use for selecting pivot.
038     * @param seed Seed for initializing the RNG.
039     *
040     * @since 4.0
041     */
042    public RandomPivotingStrategy(RandomSource randomSource,
043                                  long seed) {
044        this.randomSource = randomSource;
045        random = randomSource.create(seed);
046    }
047
048    /**
049     * {@inheritDoc}
050     *
051     * A uniform random pivot selection between begin and end indices.
052     *
053     * @return The index corresponding to a random uniformly selected
054     * value between first and the last indices of the array slice
055     * @throws org.apache.commons.math4.legacy.exception.MathIllegalArgumentException MathIllegalArgumentException when indices exceeds range
056     */
057    @Override
058    public int pivotIndex(final double[] work, final int begin, final int end) {
059        MathArrays.verifyValues(work, begin, end - begin);
060        return begin + random.nextInt(end - begin - 1);
061    }
062}