IStructuralComparable.CompareTo(Object, IComparer) Method
Definition
Important
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Determines whether the current collection object precedes, occurs in the same position as, or follows another object in the sort order.
public:
int CompareTo(System::Object ^ other, System::Collections::IComparer ^ comparer);public int CompareTo (object other, System.Collections.IComparer comparer);public int CompareTo (object? other, System.Collections.IComparer comparer);abstract member CompareTo : obj * System.Collections.IComparer -> intPublic Function CompareTo (other As Object, comparer As IComparer) As IntegerParameters
- other
- Object
The object to compare with the current instance.
- comparer
- IComparer
An object that compares members of the current collection object with the corresponding members of other.
Returns
A signed integer that indicates the relationship of the current collection object to other in the sort order:
- If less than 0, the current instance precedes other.
- If 0, the current instance and other are equal.
- If greater than 0, the current instance follows other.
| Return value | Description |
|---|---|
| -1 | The current instance precedes other.
|
| 0 | The current instance and other are equal.
|
| 1 | The current instance follows other.
|
Exceptions
This instance and other are not the same type.
Examples
The following example creates an array of Tuple<T1,T2,T3,T4,T5,T6> objects that contains population data for three U.S. cities from 1960 to 2000. The sextuple's first component is the city name. The remaining five components represent the population at ten-year intervals from 1960 to 2000.
The PopulationComparer class provides an IComparer implementation that allows the array of sextuples to be sorted by any one of its components. Two values are provided to the PopulationComparer class in its constructor: the position of the component that defines the sort order, and a Boolean value that indicates whether the tuple objects should be sorted in ascending or descending order.
The example then displays the elements in the array in unsorted order, sorts them by the third component (the population in 1970) and displays them, and then sorts them by the sixth component (the population in 2000) and displays them. Note that the example does not directly call the IStructuralComparable.CompareTo implementation. The method is called implicitly by the Sort(Array, IComparer) method for each tuple object in the array.
using System;
using System.Collections;
using System.Collections.Generic;
public class PopulationComparer<T1, T2, T3, T4, T5, T6> : IComparer
{
private int itemPosition;
private int multiplier = -1;
public PopulationComparer(int component) : this(component, true)
{ }
public PopulationComparer(int component, bool descending)
{
if (! descending) multiplier = 1;
if (component <= 0 || component > 6)
throw new ArgumentException("The component argument is out of range.");
itemPosition = component;
}
public int Compare(object x, object y)
{
var tX = x as Tuple<T1, T2, T3, T4, T5, T6>;
if (tX == null)
{
return 0;
}
else
{
var tY = y as Tuple<T1, T2, T3, T4, T5, T6>;
switch (itemPosition)
{
case 1:
return Comparer<T1>.Default.Compare(tX.Item1, tY.Item1) * multiplier;
case 2:
return Comparer<T2>.Default.Compare(tX.Item2, tY.Item2) * multiplier;
case 3:
return Comparer<T3>.Default.Compare(tX.Item3, tY.Item3) * multiplier;
case 4:
return Comparer<T4>.Default.Compare(tX.Item4, tY.Item4) * multiplier;
case 5:
return Comparer<T5>.Default.Compare(tX.Item5, tY.Item5) * multiplier;
case 6:
return Comparer<T6>.Default.Compare(tX.Item6, tY.Item6) * multiplier;
default:
return Comparer<T1>.Default.Compare(tX.Item1, tY.Item1) * multiplier;
}
}
}
}
public class Example
{
public static void Main()
{
// Create array of sextuple with population data for three U.S.
// cities, 1960-2000.
Tuple<string, int, int, int, int, int>[] cities =
{ Tuple.Create("Los Angeles", 2479015, 2816061, 2966850, 3485398, 3694820),
Tuple.Create("New York", 7781984, 7894862, 7071639, 7322564, 8008278),
Tuple.Create("Chicago", 3550904, 3366957, 3005072, 2783726, 2896016) };
// Display array in unsorted order.
Console.WriteLine("In unsorted order:");
foreach (var city in cities)
Console.WriteLine(city.ToString());
Console.WriteLine();
Array.Sort(cities, new PopulationComparer<string, int, int, int, int, int>(3));
// Display array in sorted order.
Console.WriteLine("Sorted by population in 1970:");
foreach (var city in cities)
Console.WriteLine(city.ToString());
Console.WriteLine();
Array.Sort(cities, new PopulationComparer<string, int, int, int, int, int>(6));
// Display array in sorted order.
Console.WriteLine("Sorted by population in 2000:");
foreach (var city in cities)
Console.WriteLine(city.ToString());
}
}
// The example displays the following output:
// In unsorted order:
// (Los Angeles, 2479015, 2816061, 2966850, 3485398, 3694820)
// (New York, 7781984, 7894862, 7071639, 7322564, 8008278)
// (Chicago, 3550904, 3366957, 3005072, 2783726, 2896016)
//
// Sorted by population in 1970:
// (New York, 7781984, 7894862, 7071639, 7322564, 8008278)
// (Chicago, 3550904, 3366957, 3005072, 2783726, 2896016)
// (Los Angeles, 2479015, 2816061, 2966850, 3485398, 3694820)
//
// Sorted by population in 2000:
// (New York, 7781984, 7894862, 7071639, 7322564, 8008278)
// (Los Angeles, 2479015, 2816061, 2966850, 3485398, 3694820)
// (Chicago, 3550904, 3366957, 3005072, 2783726, 2896016)
Imports System.Collections
Imports System.Collections.Generic
Public Class PopulationComparer(Of T1, T2, T3, T4, T5, T6) : Implements IComparer
Private itemPosition As Integer
Private multiplier As Integer = -1
Public Sub New(component As Integer)
Me.New(component, True)
End Sub
Public Sub New(component As Integer, descending As Boolean)
If Not descending Then multiplier = 1
If component <= 0 Or component > 6 Then
Throw New ArgumentException("The component argument is out of range.")
End If
itemPosition = component
End Sub
Public Function Compare(x As Object, y As Object) As Integer _
Implements IComparer.Compare
Dim tX = TryCast(x, Tuple(Of T1, T2, T3, T4, T5, T6))
If tX Is Nothing Then
Return 0
Else
Dim tY = DirectCast(y, Tuple(Of T1, T2, T3, T4, T5, T6))
Select Case itemPosition
Case 1
Return Comparer(Of T1).Default.Compare(tX.Item1, tY.Item1) * multiplier
Case 2
Return Comparer(Of T2).Default.Compare(tX.Item2, tY.Item2) * multiplier
Case 3
Return Comparer(Of T3).Default.Compare(tX.Item3, tY.Item3) * multiplier
Case 4
Return Comparer(Of T4).Default.Compare(tX.Item4, tY.Item4) * multiplier
Case 5
Return Comparer(Of T5).Default.Compare(tX.Item5, tY.Item5) * multiplier
Case 6
Return Comparer(Of T6).Default.Compare(tX.Item6, tY.Item6) * multiplier
' This should never happen.
Case Else
Return 0
End Select
End If
End Function
End Class
Module Example
Public Sub Main()
' Create array of sextuple with population data for three U.S.
' cities, 1960-2000.
Dim cities() =
{ Tuple.Create("Los Angeles", 2479015, 2816061, 2966850, 3485398, 3694820),
Tuple.Create("New York", 7781984, 7894862, 7071639, 7322564, 8008278),
Tuple.Create("Chicago", 3550904, 3366957, 3005072, 2783726, 2896016) }
' Display array in unsorted order.
Console.WriteLine("In unsorted order:")
For Each city In cities
Console.WriteLine(city.ToString())
Next
Console.WriteLine()
Array.Sort(cities, New PopulationComparer(Of String, Integer, Integer, Integer, Integer, Integer)(3))
' Display array in sorted order.
Console.WriteLine("Sorted by population in 1970:")
For Each city In cities
Console.WriteLine(city.ToString())
Next
Console.WriteLine()
Array.Sort(cities, New PopulationComparer(Of String, Integer, Integer, Integer, Integer, Integer)(6))
' Display array in sorted order.
Console.WriteLine("Sorted by population in 2000:")
For Each city In cities
Console.WriteLine(city.ToString())
Next
End Sub
End Module
' The example displays the following output:
' In unsorted order:
' (Los Angeles, 2479015, 2816061, 2966850, 3485398, 3694820)
' (New York, 7781984, 7894862, 7071639, 7322564, 8008278)
' (Chicago, 3550904, 3366957, 3005072, 2783726, 2896016)
'
' Sorted by population in 1970:
' (New York, 7781984, 7894862, 7071639, 7322564, 8008278)
' (Chicago, 3550904, 3366957, 3005072, 2783726, 2896016)
' (Los Angeles, 2479015, 2816061, 2966850, 3485398, 3694820)
'
' Sorted by population in 2000:
' (New York, 7781984, 7894862, 7071639, 7322564, 8008278)
' (Los Angeles, 2479015, 2816061, 2966850, 3485398, 3694820)
' (Chicago, 3550904, 3366957, 3005072, 2783726, 2896016)
Remarks
The CompareTo method supports custom structural comparison and sorting of array and tuple objects. The CompareTo method calls the comparer object's IComparer.Compare method to compare individual array elements or tuple components, starting with the first element or component. The individual calls to IComparer.Compare end and the CompareTo method returns a value when one of the following conditions becomes true:
The IComparer.Compare method returns -1.
The IComparer.Compare method returns 1.
The IComparer.Compare method is called for the last element or component in the collection object.
