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List<T>::Sort Method (Comparison<T>)

Sorts the elements in the entire List<T> using the specified System::Comparison<T>.

Namespace:  System.Collections.Generic
Assemblies:   mscorlib (in mscorlib.dll)
  System.Collections (in System.Collections.dll)

public:
void Sort(
	Comparison<T>^ comparison
)

Parameters

comparison
Type: System::Comparison<T>

The System::Comparison<T> to use when comparing elements.

ExceptionCondition
ArgumentNullException

comparison is nullptr.

ArgumentException

The implementation of comparison caused an error during the sort. For example, comparison might not return 0 when comparing an item with itself.

If comparison is provided, the elements of the List<T> are sorted using the method represented by the delegate.

If comparison is nullptr, an ArgumentNullException is thrown.

This method uses Array::Sort, , which applies the introspective sort as follows:

  • If the partition size is fewer than 16 elements, it uses an insertion sort algorithm

  • If the number of partitions exceeds 2 * LogN, where N is the range of the input array, it uses a Heapsort algorithm.

  • Otherwise, it uses a 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 demonstrates the Sort and Sort method overloads on a simple business object. Calling the Sort method results in the use of the default comparer for the Part type, and the Sort method is implemented using an anonymous method.

No code example is currently available or this language may not be supported.

The following example demonstrates the Sort(Comparison<T>) method overload.

The example defines an alternative comparison method for strings, named CompareDinosByLength. This method works as follows: First, the comparands are tested for nullptr, 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 four strings, in no particular order. The list also includes an empty string and a null reference. The list is displayed, sorted using a Comparison<T> generic delegate representing the CompareDinosByLength method, and displayed again.

using namespace System;
using namespace System::Collections::Generic;

int CompareDinosByLength(String^ x, String^ y)
{
    if (x == nullptr)
    {
        if (y == nullptr)
        {
            // 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 == nullptr)
            // ...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);
            }
        }
    }
};

void Display(List<String^>^ list)
{
    Console::WriteLine();
    for each(String^ s in list)
    {
        if (s == nullptr)
            Console::WriteLine("(null)");
        else
            Console::WriteLine("\"{0}\"", s);
    }
};

void main()
{
    List<String^>^ dinosaurs = gcnew List<String^>();
    dinosaurs->Add("Pachycephalosaurus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("");
    dinosaurs->Add(nullptr);
    dinosaurs->Add("Mamenchisaurus");
    dinosaurs->Add("Deinonychus");
    Display(dinosaurs);

    Console::WriteLine("\nSort with generic Comparison<String^> delegate:");
    dinosaurs->Sort(
        gcnew Comparison<String^>(CompareDinosByLength));
    Display(dinosaurs);

}

/* This code example produces the following output:

"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"

Sort with generic Comparison<String^> delegate:

(null)
""
"Deinonychus"
"Amargasaurus"
"Mamenchisaurus"
"Pachycephalosaurus"
 */

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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