[7363] | 1 | #region License Information
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| 2 | /* HeuristicLab
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| 3 | * Copyright (C) 2002-2012 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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| 4 | *
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| 5 | * This file is part of HeuristicLab.
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| 6 | *
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| 7 | * HeuristicLab is free software: you can redistribute it and/or modify
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| 8 | * it under the terms of the GNU General Public License as published by
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| 9 | * the Free Software Foundation, either version 3 of the License, or
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| 10 | * (at your option) any later version.
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| 11 | *
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| 12 | * HeuristicLab is distributed in the hope that it will be useful,
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| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 15 | * GNU General Public License for more details.
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| 16 | *
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| 17 | * You should have received a copy of the GNU General Public License
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| 18 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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| 19 | */
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| 20 | #endregion
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| 21 |
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[7407] | 22 | using System;
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[7363] | 23 | using System.Collections.Generic;
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| 24 | using System.Linq;
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| 25 | using HeuristicLab.Core;
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| 26 |
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| 27 | namespace HeuristicLab.Problems.GeneralizedQuadraticAssignment.Common {
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| 28 | public static class ExtensionMethods {
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[7407] | 29 |
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[7363] | 30 | /// <summary>
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[7407] | 31 | /// Simply enumerates the sequence by moving over all elements.
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[7363] | 32 | /// </summary>
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[7407] | 33 | /// <typeparam name="T">The type of the items that are to be enumerated.</typeparam>
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| 34 | /// <param name="source">The enumerable that contains the items.</param>
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| 35 | public static void Enumerate<T>(this IEnumerable<T> source) {
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| 36 | var enumerator = source.GetEnumerator();
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| 37 | while (enumerator.MoveNext()) ;
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| 38 | }
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| 39 |
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| 40 | /// <summary>
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| 41 | /// Selects an element from an enumerable randomly with equal probability for each element. If the sequence is empty, selected will be false and default(T) will be returned.
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| 42 | /// </summary>
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[7363] | 43 | /// <typeparam name="T">The type of the items that are to be selected.</typeparam>
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| 44 | /// <param name="source">The enumerable that contains the items.</param>
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| 45 | /// <param name="random">The random number generator, its NextDouble() method must return a value in the range [0;1).</param>
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[7407] | 46 | /// <param name="selected">True if an element was selected, false otherwise (only because of an empty sequence).</param>
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[7363] | 47 | /// <returns>The selected item.</returns>
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[7407] | 48 | public static T ChooseRandomOrDefault<T>(this IEnumerable<T> source, IRandom random, out bool selected) {
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| 49 | if (source == null) throw new ArgumentNullException("SelectRandomOrDefault: source is null");
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| 50 | uint counter = 1;
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[7363] | 51 | selected = false;
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| 52 | T selectedItem = default(T);
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| 53 | foreach (T item in source) {
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[7407] | 54 | if (counter * random.NextDouble() < 1.0) { // use multiplication instead of division
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[7363] | 55 | selectedItem = item;
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| 56 | selected = true;
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| 57 | }
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[7407] | 58 | counter++;
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[7363] | 59 | }
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| 60 | return selectedItem;
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| 61 | }
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| 62 |
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| 63 | /// <summary>
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[7407] | 64 | /// Selects an element from an enumerable randomly with equal probability for each element.
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| 65 | /// </summary>
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| 66 | /// <typeparam name="T">The type of the items that are to be selected.</typeparam>
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| 67 | /// <param name="source">The enumerable that contains the items.</param>
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| 68 | /// <param name="random">The random number generator, its NextDouble() method must return a value in the range [0;1).</param>
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| 69 | /// <returns>The selected item.</returns>
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| 70 | public static T ChooseRandom<T>(this IEnumerable<T> source, IRandom random) {
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| 71 | if (source == null) throw new ArgumentNullException("SelectRandom: source is null");
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| 72 | if (!source.Any()) throw new ArgumentException("SelectRandom: sequence is empty.");
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| 73 | uint counter = 1;
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| 74 | T selectedItem = default(T);
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| 75 | foreach (T item in source) {
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| 76 | if (counter * random.NextDouble() < 1.0) // use multiplication instead of division
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| 77 | selectedItem = item;
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| 78 | counter++;
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| 79 | }
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| 80 | return selectedItem;
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| 81 | }
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| 82 |
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| 83 | /// <summary>
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[7363] | 84 | /// Shuffles an enumerable and returns an new enumerable according to the Fisher-Yates shuffle.
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| 85 | /// </summary>
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| 86 | /// <remarks>
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| 87 | /// Source code taken from http://stackoverflow.com/questions/1287567/c-is-using-random-and-orderby-a-good-shuffle-algorithm.
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| 88 | /// Note that this is an online shuffle, but the source enumerable is transformed into an array.
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| 89 | /// </remarks>
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| 90 | /// <typeparam name="T">The type of the items that are to be shuffled.</typeparam>
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| 91 | /// <param name="source">The enumerable that contains the items.</param>
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| 92 | /// <param name="random">The random number generator, its Next(int) method must deliver uniformly distributed random numbers.</param>
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| 93 | /// <returns>An enumerable with the elements shuffled.</returns>
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| 94 | public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source, IRandom random) {
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| 95 | T[] elements = source.ToArray();
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| 96 | // Note i > 0 to avoid final pointless iteration
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| 97 | for (int i = elements.Length - 1; i > 0; i--) {
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| 98 | // Swap element "i" with a random earlier element it (or itself)
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| 99 | int swapIndex = random.Next(i + 1);
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| 100 | yield return elements[swapIndex];
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| 101 | elements[swapIndex] = elements[i];
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| 102 | // we don't actually perform the swap, we can forget about the
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| 103 | // swapped element because we already returned it.
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| 104 | }
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| 105 |
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| 106 | // there is one item remaining that was not returned - we return it now
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| 107 | yield return elements[0];
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| 108 | }
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| 109 |
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| 110 | /// <summary>
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| 111 | /// Walks an operator graph in that it jumps from one operator to all its operator parameters and yields each operator it touches.
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| 112 | /// Cycles are detected and not walked twice.
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| 113 | /// </summary>
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| 114 | /// <param name="initial">The operator where the walk starts (is also yielded).</param>
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| 115 | /// <returns>An enumeration of all the operators that could be found.</returns>
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| 116 | public static IEnumerable<IOperator> Walk(this IOperator initial) {
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| 117 | var open = new Stack<IOperator>();
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| 118 | var visited = new HashSet<IOperator>();
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| 119 | open.Push(initial);
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| 120 |
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| 121 | while (open.Any()) {
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| 122 | IOperator current = open.Pop();
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| 123 | if (visited.Contains(current)) continue;
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| 124 | visited.Add(current);
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| 125 |
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| 126 | foreach (var parameter in current.Parameters.OfType<IValueParameter>()) {
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| 127 | if (typeof(IOperator).IsAssignableFrom(parameter.DataType)) {
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| 128 | if (parameter.Value != null)
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| 129 | open.Push((IOperator)parameter.Value);
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| 130 | }
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| 131 | }
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| 132 |
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| 133 | yield return current;
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| 134 | }
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| 135 | }
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| 136 |
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| 137 | }
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| 138 | }
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