List<T>.Sort Method (Int32, Int32, IComparer<T>)
Sorts the elements in a range of elements in List<T> using the specified comparer.
Namespace: System.Collections.Generic
Assembly: mscorlib (in mscorlib.dll)
Parameters
- index
- Type: System.Int32
The zero-based starting index of the range to sort.
- count
- Type: System.Int32
The length of the range to sort.
- comparer
- Type: System.Collections.Generic.IComparer<T>
The IComparer<T> implementation to use when comparing elements, or null to use the default comparer Comparer<T>.Default.
| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | index is less than 0. -or- count is less than 0. |
| ArgumentException | index and count do not specify a valid range in the List<T>. -or- The implementation of comparer caused an error during the sort. For example, comparer might not return 0 when comparing an item with itself. |
| InvalidOperationException | comparer is null, and the default comparer Comparer<T>.Default cannot find implementation of the IComparable<T> generic interface or the IComparable interface for type T. |
If comparer is provided, the elements of the List<T> are sorted using the specified IComparer<T> implementation.
If comparer is null, the default comparer Comparer<T>.Default checks whether type T implements the IComparable<T> generic interface and uses that implementation, if available. If not, Comparer<T>.Default checks whether type T implements the IComparable interface. If type T does not implement either interface, Comparer<T>.Default throws an InvalidOperationException.
This method uses Array.Sort, which uses the QuickSort algorithm. This implementation performs an unstable sort; that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal.
On average, this method is an O(n log n) operation, where n is Count; in the worst case it is an O(n ^ 2) operation.
The following code example demonstrates the Sort(Int32, Int32, IComparer<T>) method overload and the BinarySearch(Int32, Int32, T, IComparer<T>) method overload.
The code example defines an alternative comparer for strings named DinoCompare, which implements the IComparer<string> (IComparer(Of String) in Visual Basic, IComparer<String^> in Visual C++) generic interface. The comparer works as follows: First, the comparands are tested for null, and a null reference is treated as less than a non-null. Second, the string lengths are compared, and the longer string is deemed to be greater. Third, if the lengths are equal, ordinary string comparison is used.
A List<T> of strings is created and populated with the names of five herbivorous dinosaurs and three carnivorous dinosaurs. Within each of the two groups, the names are not in any particular sort order. The list is displayed, the range of herbivores is sorted using the alternate comparer, and the list is displayed again.
The BinarySearch(Int32, Int32, T, IComparer<T>) method overload is then used to search only the range of herbivores for "Brachiosaurus". The string is not found, and the bitwise complement (the ~ operator in C# and Visual C++, Xor -1 in Visual Basic) of the negative number returned by the BinarySearch(Int32, Int32, T, IComparer<T>) method is used as an index for inserting the new string.
using System; using System.Collections.Generic; public class DinoComparer: IComparer<string> { public int Compare(string x, string y) { if (x == null) { if (y == null) { // If x is null and y is null, they're // equal. return 0; } else { // If x is null and y is not null, y // is greater. return -1; } } else { // If x is not null... // if (y == null) // ...and y is null, x is greater. { return 1; } else { // ...and y is not null, compare the // lengths of the two strings. // int retval = x.Length.CompareTo(y.Length); if (retval != 0) { // If the strings are not of equal length, // the longer string is greater. // return retval; } else { // If the strings are of equal length, // sort them with ordinary string comparison. // return x.CompareTo(y); } } } } } public class Example { public static void Main() { List<string> dinosaurs = new List<string>(); dinosaurs.Add("Pachycephalosaurus"); dinosaurs.Add("Parasauralophus"); dinosaurs.Add("Amargasaurus"); dinosaurs.Add("Galimimus"); dinosaurs.Add("Mamenchisaurus"); dinosaurs.Add("Deinonychus"); dinosaurs.Add("Oviraptor"); dinosaurs.Add("Tyrannosaurus"); int herbivores = 5; Display(dinosaurs); DinoComparer dc = new DinoComparer(); Console.WriteLine("\nSort a range with the alternate comparer:"); dinosaurs.Sort(0, herbivores, dc); Display(dinosaurs); Console.WriteLine("\nBinarySearch a range and Insert \"{0}\":", "Brachiosaurus"); int index = dinosaurs.BinarySearch(0, herbivores, "Brachiosaurus", dc); if (index < 0) { dinosaurs.Insert(~index, "Brachiosaurus"); herbivores++; } Display(dinosaurs); } private static void Display(List<string> list) { Console.WriteLine(); foreach( string s in list ) { Console.WriteLine(s); } } } /* This code example produces the following output: Pachycephalosaurus Parasauralophus Amargasaurus Galimimus Mamenchisaurus Deinonychus Oviraptor Tyrannosaurus Sort a range with the alternate comparer: Galimimus Amargasaurus Mamenchisaurus Parasauralophus Pachycephalosaurus Deinonychus Oviraptor Tyrannosaurus BinarySearch a range and Insert "Brachiosaurus": Galimimus Amargasaurus Brachiosaurus Mamenchisaurus Parasauralophus Pachycephalosaurus Deinonychus Oviraptor Tyrannosaurus */
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
