mcs/class/System.Core/System.Linq/InternalOrderedSequence.cs

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   2 // a copy of this software and associated documentation files (the
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   6 // permit persons to whom the Software is furnished to do so, subject to
   7 // the following conditions:
   8 //
   9 // The above copyright notice and this permission notice shall be
  10 // included in all copies or substantial portions of the Software.
  11 //
  12 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  13 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  14 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  15 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  16 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  17 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  18 //
  19 // Authors:
  20 //        Alejandro Serrano "Serras" (trupill@yahoo.es)
  21 //
  22
  23 using System;
  24 using System.Collections;
  25 using System.Collections.Generic;
  26
  27 namespace System.Linq
  28 {
  29         internal class InternalOrderedSequence<TElement, K> : IOrderedEnumerable<TElement>
  30         {
  31                 IEnumerable<TElement> source;
  32                 Func<TElement, K> key_selector;
  33                 IComparer<K> comparer;
  34                 bool descending;
  35                 IOrderedEnumerable<TElement> previous;
  36
  37                 internal InternalOrderedSequence (IEnumerable<TElement> source, Func<TElement, K> keySelector,
  38                                                   IComparer<K> comparer, bool descending, IOrderedEnumerable<TElement> previous)
  39                 {
  40                         this.source = source;
  41                         this.key_selector = keySelector;
  42                         this.comparer = comparer;
  43                         this.descending = descending;
  44                         this.previous = previous;
  45                 }
  46
  47
  48                 IEnumerable<TElement> Sort (IEnumerable<TElement> previousList)
  49                 {
  50                         if (previous == null)
  51                                 return PerformSort (previousList);
  52
  53                        return previous.CreateOrderedEnumerable (key_selector, comparer, descending);
  54                 }
  55
  56                 public IEnumerator<TElement> GetEnumerator ()
  57                 {
  58                         return Sort (source).GetEnumerator ();
  59                 }
  60
  61                 IEnumerator IEnumerable.GetEnumerator ()
  62                 {
  63                         return this.GetEnumerator ();
  64                 }
  65
  66                 public IOrderedEnumerable<TElement> CreateOrderedEnumerable<TKey> (
  67                         Func<TElement, TKey> selector, IComparer<TKey> comparer, bool descending)
  68                 {
  69                         throw new NotImplementedException ();
  70                 }
  71
  72                 List<TElement> source_list;
  73                 K[] keys;
  74                 int[] indexes;
  75
  76                 private IEnumerable<TElement> PerformSort (IEnumerable<TElement> items)
  77                 {
  78                         // It first enumerates source, collecting all elements
  79                         source_list = new List<TElement> (items);
  80
  81                         // If the source contains just zero or one element, there's no need to sort
  82                         if (source_list.Count <= 1)
  83                                 return source_list;
  84
  85                         // Then evaluate the keySelector function for each element,
  86                         // collecting the key values
  87                         keys = new K [source_list.Count];
  88                         for (int i = 0; i < source_list.Count; i++)
  89                                 keys[i] = key_selector(source_list [i]);
  90
  91                         // Then sorts the elements according to the collected
  92                         // key values and the selected ordering
  93                         indexes = new int [keys.Length];
  94                         for (int i = 0; i < indexes.Length; i++)
  95                                 indexes [i] = i;
  96
  97                         QuickSort(indexes, 0, indexes.Length - 1);
  98
  99                         // Return the values as IEnumerable<TElement>
 100                         TElement[] orderedList = new TElement [indexes.Length];
 101                         for (int i = 0; i < indexes.Length; i++)
 102                                 orderedList [i] = source_list [indexes [i]];
 103                         return orderedList;
 104                 }
 105
 106                 private int CompareItems (int firstIndex, int secondIndex)
 107                 {
 108                         int comparison;
 109
 110                         if (comparer == null)
 111                                 comparison = ((IComparable<K>)keys [firstIndex]).CompareTo (keys [secondIndex]);
 112                         else
 113                                 comparison =  comparer.Compare (keys [firstIndex], keys [secondIndex]);
 114
 115                         // If descending, return the opposite comparison
 116                         return (descending ? -comparison : comparison);
 117                 }
 118
 119                 /** QuickSort implementation
 120                     Based on implementation found in Wikipedia
 121                     http://en.wikipedia.org/wiki/Quicksort_implementations
 122                     that was released under the GNU Free Documentation License **/
 123
 124                 private void QuickSort (int[] array, int left, int right)
 125                 {
 126                         int lhold = left;
 127                         int rhold = right;
 128                         Random random = new Random ();
 129                         int pivot = random.Next (left, right);
 130                         Swap (array, pivot, left);
 131                         pivot = left;
 132                         left++;
 133
 134                         while (right >= left) {
 135                                 int leftComparison = CompareItems (indexes [left], indexes [pivot]);
 136                                 int rightComparison = CompareItems (indexes [right], indexes [pivot]);
 137                                 if (leftComparison >= 0 && rightComparison < 0)
 138                                         Swap (array, left, right);
 139                                 else if (leftComparison >= 0)
 140                                         right--;
 141                                 else if (rightComparison < 0)
 142                                         left++;
 143                                 else {
 144                                         right--;
 145                                         left++;
 146                                 }
 147                         }
 148
 149                         Swap (array, pivot, right);
 150                         pivot = right;
 151                         if (pivot > lhold)
 152                                 QuickSort (array, lhold, pivot);
 153                         if (rhold > pivot + 1)
 154                                 QuickSort (array, pivot + 1, rhold);
 155                 }
 156
 157                 private void Swap (int[] items, int left, int right)
 158                 {
 159                         int temp = items [right];
 160                         items [right] = items [left];
 161                         items [left] = temp;
 162                 }
 163
 164         }
 165 }