Changeset 7407 for branches/GeneralizedQAP/HeuristicLab.Problems.GeneralizedQuadraticAssignment.Common/3.3

Timestamp:

01/24/12 17:23:21 (13 years ago)

Author:

abeham

Message:

#1614: worked on GQAP

File:

• branches/GeneralizedQAP/HeuristicLab.Problems.GeneralizedQuadraticAssignment.Common/3.3/ExtensionMethods.cs (modified) (3 diffs)

branches/GeneralizedQAP/HeuristicLab.Problems.GeneralizedQuadraticAssignment.Common/3.3/ExtensionMethods.cs

@@ -20 +20 @@
 #endregion
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -26 +27 @@
 namespace HeuristicLab.Problems.GeneralizedQuadraticAssignment.Common {
   public static class ExtensionMethods {
+
+    /// <summary>
+    /// Simply enumerates the sequence by moving over all elements.
+    /// </summary>
+    /// <typeparam name="T">The type of the items that are to be enumerated.</typeparam>
+    /// <param name="source">The enumerable that contains the items.</param>
+    public static void Enumerate<T>(this IEnumerable<T> source) {
+      var enumerator = source.GetEnumerator();
+      while (enumerator.MoveNext()) ;
+    }
+
+    /// <summary>
+    /// 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.
+    /// </summary>
+    /// <typeparam name="T">The type of the items that are to be selected.</typeparam>
+    /// <param name="source">The enumerable that contains the items.</param>
+    /// <param name="random">The random number generator, its NextDouble() method must return a value in the range [0;1).</param>
+    /// <param name="selected">True if an element was selected, false otherwise (only because of an empty sequence).</param>
+    /// <returns>The selected item.</returns>
+    public static T ChooseRandomOrDefault<T>(this IEnumerable<T> source, IRandom random, out bool selected) {
+      if (source == null) throw new ArgumentNullException("SelectRandomOrDefault: source is null");
+      uint counter = 1;
+      selected = false;
+      T selectedItem = default(T);
+      foreach (T item in source) {
+        if (counter * random.NextDouble() < 1.0) { // use multiplication instead of division
+          selectedItem = item;
+          selected = true;
+        }
+        counter++;
+      }
+      return selectedItem;
+    }
+
     /// <summary>
     /// Selects an element from an enumerable randomly with equal probability for each element.
@@ -32 +67 @@
     /// <param name="source">The enumerable that contains the items.</param>
     /// <param name="random">The random number generator, its NextDouble() method must return a value in the range [0;1).</param>
-    /// <param name="selected">True if an element was selected, false otherwise (mainly because of an empty sequence).</param>
     /// <returns>The selected item.</returns>
-    public static T SelectRandomOrDefault<T>(this IEnumerable<T> source, IRandom random, out bool selected) {
-      int counter = 1;
-      selected = false;
+    public static T ChooseRandom<T>(this IEnumerable<T> source, IRandom random) {
+      if (source == null) throw new ArgumentNullException("SelectRandom: source is null");
+      if (!source.Any()) throw new ArgumentException("SelectRandom: sequence is empty.");
+      uint counter = 1;
       T selectedItem = default(T);
       foreach (T item in source) {
-        if (random.NextDouble() < 1.0 / counter) {
+        if (counter * random.NextDouble() < 1.0) // use multiplication instead of division
           selectedItem = item;
-          selected = true;
-        }
+        counter++;
       }
       return selectedItem;