Comparison<T> Delegate
Represents the method that compares two objects of the same type.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- x
-
Type:
T
The first object to compare.
- y
-
Type:
T
The second object to compare.
Return Value
Type: System.Int32A signed integer that indicates the relative values of x and y, as shown in the following table.
Value | Meaning |
|---|---|
Less than 0 | x is less than y. |
0 | x equals y. |
Greater than 0 | x is greater than y. |
Type Parameters
- in T
The type of the objects to compare.
This delegate is used by the Sort<T>(T[], Comparison<T>) method overload of the Array class and the Sort(Comparison<T>) method overload of the List<T> class to sort the elements of an array or list.
The following code example demonstrates the use of the Comparison<T> delegate with the Sort(Comparison<T>) method overload.
The code example defines an alternative comparison method for strings, named CompareDinosByLength. This method 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 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 System; using System.Collections.Generic; public class Example { private static int CompareDinosByLength(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 static void Main() { List<string> dinosaurs = new List<string>(); dinosaurs.Add("Pachycephalosaurus"); dinosaurs.Add("Amargasaurus"); dinosaurs.Add(""); dinosaurs.Add(null); dinosaurs.Add("Mamenchisaurus"); dinosaurs.Add("Deinonychus"); Display(dinosaurs); Console.WriteLine("\nSort with generic Comparison<string> delegate:"); dinosaurs.Sort(CompareDinosByLength); Display(dinosaurs); } private static void Display(List<string> list) { Console.WriteLine(); foreach( string s in list ) { if (s == null) Console.WriteLine("(null)"); else Console.WriteLine("\"{0}\"", s); } } } /* This code example produces the following output: "Pachycephalosaurus" "Amargasaurus" "" (null) "Mamenchisaurus" "Deinonychus" Sort with generic Comparison<string> delegate: (null) "" "Deinonychus" "Amargasaurus" "Mamenchisaurus" "Pachycephalosaurus" */
The following example uses the Comparison<T> delegate to sort the elements of a collection of CityInfo objects. CityInfo is an application-defined class that contains information about a city and its population. The example defines three methods, CompareByName, CompareByPopulation, and CompareByNames, that offer three different ways of ordering the CityInfo objects. Each method is assigned to the comparison argument of the Array.Sort<T>(T[], Comparison<T>) method.
using System; public class CityInfo { string cityName; string countryName; int pop2010; public CityInfo(string name, string country, int pop2010) { this.cityName = name; this.countryName = country; this.pop2010 = pop2010; } public string City { get { return this.cityName; } } public string Country { get { return this.countryName; } } public int Population { get { return this.pop2010; } } public static int CompareByName(CityInfo city1, CityInfo city2) { return String.Compare(city1.City, city2.City); } public static int CompareByPopulation(CityInfo city1, CityInfo city2) { return city1.Population.CompareTo(city2.Population); } public static int CompareByNames(CityInfo city1, CityInfo city2) { return String.Compare(city1.Country + city1.City, city2.Country + city2.City); } } public class Example { public static void Main() { CityInfo NYC = new CityInfo("New York City", "United States of America", 8175133 ); CityInfo Det = new CityInfo("Detroit", "United States of America", 713777); CityInfo Paris = new CityInfo("Paris", "France", 2193031); CityInfo[] cities = { NYC, Det, Paris }; // Display ordered array. DisplayArray(cities); // Sort array by city name. Array.Sort(cities, CityInfo.CompareByName); DisplayArray(cities); // Sort array by population. Array.Sort(cities, CityInfo.CompareByPopulation); DisplayArray(cities); // Sort array by country + city name. Array.Sort(cities, CityInfo.CompareByNames); DisplayArray(cities); } private static void DisplayArray(CityInfo[] cities) { Console.WriteLine("{0,-20} {1,-25} {2,10}", "City", "Country", "Population"); foreach (var city in cities) Console.WriteLine("{0,-20} {1,-25} {2,10:N0}", city.City, city.Country, city.Population); Console.WriteLine(); } } // The example displays the following output: // City Country Population // New York City United States of America 8,175,133 // Detroit United States of America 713,777 // Paris France 2,193,031 // // City Country Population // Detroit United States of America 713,777 // New York City United States of America 8,175,133 // Paris France 2,193,031 // // City Country Population // Detroit United States of America 713,777 // Paris France 2,193,031 // New York City United States of America 8,175,133 // // City Country Population // Paris France 2,193,031 // Detroit United States of America 713,777 // New York City United States of America 8,175,133
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1