11using System . Collections ;
22using System . Collections . Generic ;
3+ #if NET35
4+ using System . Linq ;
5+ #endif
36#if PCL
47using ArrayList = System . Collections . Generic . List < object > ;
58#endif
@@ -12,7 +15,7 @@ namespace NetTopologySuite.Utilities
1215 /// </summary>
1316 public class CollectionUtil
1417 {
15-
18+
1619 /// <summary>
1720 ///
1821 /// </summary>
@@ -40,7 +43,7 @@ public class CollectionUtil
4043 public static IList Transform ( ICollection coll , FunctionDelegate < object > func )
4144 {
4245 IList result = new ArrayList ( ) ;
43- foreach ( object obj in coll )
46+ foreach ( object obj in coll )
4447 result . Add ( func ( obj ) ) ;
4548 return result ;
4649 }
@@ -140,10 +143,10 @@ public static void Apply<T>(IEnumerable<T> coll, FunctionDelegate<T> func)
140143 /// <returns></returns>
141144 public static IList Select ( ICollection coll , FunctionDelegate < object , bool > func )
142145 {
143- IList result = new ArrayList ( ) ;
146+ IList result = new ArrayList ( ) ;
144147 foreach ( object obj in coll )
145148 if ( func ( obj ) )
146- result . Add ( obj ) ;
149+ result . Add ( obj ) ;
147150 return result ;
148151 }
149152
@@ -177,5 +180,74 @@ public static TOut[] Cast<TIn,TOut>(TIn[] array)
177180 return res ;
178181 }
179182
183+ internal static IEnumerable < T > StableSort < T > ( IEnumerable < T > items )
184+ {
185+ return StableSort ( items , Comparer < T > . Default ) ;
186+ }
187+
188+ internal static IEnumerable < T > StableSort < T > ( IEnumerable < T > items , IComparer < T > comparer )
189+ {
190+ #if NET35
191+ // LINQ's OrderBy is guaranteed to be a stable sort.
192+ return items . OrderBy ( x => x , comparer ) ;
193+ #else
194+
195+ // otherwise, tag each item with the index and sort the wrappers.
196+ // if we're given a collection (and we always are), use its count
197+ // to prevent unnecessary array copies.
198+ var itemCollection = items as ICollection < T > ;
199+ var taggedItems = itemCollection == null
200+ ? new List < IndexTaggedItem < T > > ( )
201+ : new List < IndexTaggedItem < T > > ( itemCollection . Count ) ;
202+
203+ int index = 0 ;
204+ foreach ( var item in items )
205+ {
206+ taggedItems . Add ( new IndexTaggedItem < T > ( item , index ++ ) ) ;
207+ }
208+
209+ taggedItems . Sort ( new IndexAwareComparer < T > ( comparer ) ) ;
210+
211+ var sorted = new List < T > ( taggedItems . Count ) ;
212+ foreach ( var taggedItem in taggedItems )
213+ {
214+ sorted . Add ( taggedItem . Item ) ;
215+ }
216+
217+ return sorted ;
218+ #endif
219+ }
220+
221+ #if ! NET35
222+ private sealed class IndexTaggedItem < T >
223+ {
224+ internal readonly T Item ;
225+ internal readonly int Index ;
226+
227+ internal IndexTaggedItem ( T item , int index )
228+ {
229+ this . Item = item ;
230+ this . Index = index ;
231+ }
232+ }
233+
234+ private sealed class IndexAwareComparer < T > : Comparer < IndexTaggedItem < T > >
235+ {
236+ private readonly IComparer < T > primaryComparer ;
237+
238+ internal IndexAwareComparer ( IComparer < T > primaryComparer )
239+ {
240+ this . primaryComparer = primaryComparer ;
241+ }
242+
243+ public override int Compare ( IndexTaggedItem < T > x , IndexTaggedItem < T > y )
244+ {
245+ int cmp = this . primaryComparer . Compare ( x . Item , y . Item ) ;
246+
247+ // compare equal elements by their index.
248+ return cmp == 0 ? x . Index . CompareTo ( y . Index ) : cmp ;
249+ }
250+ }
251+ #endif
180252 }
181253}
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