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Tuple<T1, T2>.IStructuralComparable.CompareTo Method

Compares the current Tuple<T1, T2> object to a specified object by using a specified comparer, and returns an integer that indicates whether the current object is before, after, or in the same position as the specified object in the sort order.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

int IStructuralComparable.CompareTo(
	Object other,
	IComparer comparer


Type: System.Object

An object to compare with the current instance.

Type: System.Collections.IComparer

An object that provides custom rules for comparison.

Return Value

Type: System.Int32
A signed integer that indicates the relative position of this instance and other in the sort order, as shown in the following table.



A negative integer

This instance precedes other.


This instance and other have the same position in the sort order.

A positive integer

This instance follows other.


IStructuralComparable.CompareTo(Object, IComparer)


other is not a Tuple<T1, T2> object.

This member is an explicit interface member implementation. It can be used only when the Tuple<T1, T2> instance is cast to an IStructuralComparable interface.

Although this method can be called directly, it is most commonly called by collection sorting methods that include IComparer parameters to order the members of a collection., For example, it is called by the Array.Sort(Array, IComparer) method and the Add method of a SortedList object that is instantiated by using the SortedList.SortedList(IComparer) constructor.

Caution noteCaution

The IStructuralComparable.CompareTo method is intended for use in sorting operations. It should not be used when the primary purpose of a comparison is to determine whether two objects are equal. To determine whether two objects are equal, call the IStructuralEquatable.Equals method.

The following example creates an array of Tuple<T1, T2> objects that consist of a student's name and test score. It displays the component of each tuple in the array in unsorted order, sorts the array, and then calls ToString to display the value of each tuple in sorted order. To sort the array, the example defines a generic ScoreComparer class that implements the IComparer interface and sorts the Tuple<T1, T2> objects in ascending order by the value of their second component rather than their first component. Note that the example does not directly call the IStructuralComparable.CompareTo method. This method is called implicitly by the Array.Sort(Array, IComparer) method for each element in the array.

using System;
using System.Collections;
using System.Collections.Generic;

public class ScoreComparer<T1, T2> : IComparer
   public int Compare(object x, object y)
      Tuple<T1, T2> tX = x as Tuple<T1,T2>;
      if (tX == null)
         return 0;
         Tuple<T1, T2> tY = y as Tuple<T1, T2>;
         return Comparer<T2>.Default.Compare(tX.Item2, tY.Item2);             

public class Example
   public static void Main()
      Tuple<string, Nullable<int>>[] scores = 
                    { new Tuple<string, Nullable<int>>("Jack", 78),
                      new Tuple<string, Nullable<int>>("Abbey", 92), 
                      new Tuple<string, Nullable<int>>("Dave", 88),
                      new Tuple<string, Nullable<int>>("Sam", 91), 
                      new Tuple<string, Nullable<int>>("Ed", null),
                      new Tuple<string, Nullable<int>>("Penelope", 82),
                      new Tuple<string, Nullable<int>>("Linda", 99),
                      new Tuple<string, Nullable<int>>("Judith", 84) };

      Console.WriteLine("The values in unsorted order:");
      foreach (var score in scores)


      Array.Sort(scores, new ScoreComparer<string, Nullable<int>>());

      Console.WriteLine("The values in sorted order:");
      foreach (var score in scores)
// The example displays the following output; 
//       The values in unsorted order: 
//       (Jack, 78) 
//       (Abbey, 92) 
//       (Dave, 88) 
//       (Sam, 91) 
//       (Ed, ) 
//       (Penelope, 82) 
//       (Linda, 99) 
//       (Judith, 84) 
//       The values in sorted order: 
//       (Ed, ) 
//       (Jack, 78) 
//       (Penelope, 82) 
//       (Judith, 84) 
//       (Dave, 88) 
//       (Sam, 91) 
//       (Abbey, 92) 
//       (Linda, 99)

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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