1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.math4.legacy.stat.descriptive.rank;
18
19 import org.apache.commons.math4.legacy.core.MathArrays;
20 import org.apache.commons.rng.RestorableUniformRandomProvider;
21 import org.apache.commons.rng.simple.RandomSource;
22
23 /**
24 * A strategy of selecting random index between begin and end indices.
25 *
26 * @since 3.4
27 */
28 public class RandomPivotingStrategy implements PivotingStrategy {
29 /** Source of randomness. */
30 private final RandomSource randomSource;
31 /** Random generator to use for selecting pivot. */
32 private transient RestorableUniformRandomProvider random;
33
34 /**
35 * Simple constructor.
36 *
37 * @param randomSource RNG to use for selecting pivot.
38 * @param seed Seed for initializing the RNG.
39 *
40 * @since 4.0
41 */
42 public RandomPivotingStrategy(RandomSource randomSource,
43 long seed) {
44 this.randomSource = randomSource;
45 random = randomSource.create(seed);
46 }
47
48 /**
49 * {@inheritDoc}
50 *
51 * A uniform random pivot selection between begin and end indices.
52 *
53 * @return The index corresponding to a random uniformly selected
54 * value between first and the last indices of the array slice
55 * @throws org.apache.commons.math4.legacy.exception.MathIllegalArgumentException MathIllegalArgumentException when indices exceeds range
56 */
57 @Override
58 public int pivotIndex(final double[] work, final int begin, final int end) {
59 MathArrays.verifyValues(work, begin, end - begin);
60 return begin + random.nextInt(end - begin - 1);
61 }
62 }