Quando usar comparison ou comparation

Índice Show

Extension Methods

Tempo de leitura: menos de 1 minuto

Ulisses Wehby de Carvalho

COMPARAR

Tenha cuidado na hora de escolher a preposição que acompanha o verbo “COMPARE” na língua inglesa. Quando a sua intenção for ressaltar as diferenças que porventura duas coisas semelhantes podem ter, use “COMPARE WITH”. Se, por outro lado, você quiser salientar as semelhanças apresentadas por duas pessoas, objetos, situações etc. diferentes, utilize “COMPARE TO”. Compare os exemplos. “NO PUN INTENDED!” (Sem trocadilho!)

If it is an error in the code, please compare with the original code you received.
Se for um erro no código, por favor, compare-o ao código original que você recebeu.
How does the dolphin brain compare to the human brain?
Quais são as semelhanças entre o cérebro do golfinho e o cérebro humano?

Cf. Mais Erros Comuns

Referência: “Dicionário dos Erros Mais Comuns em Inglês” de Ulisses Wehby de Carvalho – Editora Campus/Elsevier, 2005. Leia a resenha.

Leitura focada

generic <typename T> public delegate int Comparison(T x, T y); public delegate int Comparison<in T>(T x, T y); public delegate int Comparison<T>(T x, T y); type Comparison<'T> = delegate of 'T * 'T -> int Public Delegate Function Comparison(Of In T)(x As T, y As T) As Integer Public Delegate Function Comparison(Of T)(x As T, y As T) As Integer Int32

A 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.

Examples

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 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" */ 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" */ open System let compareDinosByLength (x: string) (y: string) = match x with | null when isNull y -> // If x is null and y is null, they're equal. 0 | null -> // If x is null and y is not null, y is greater. -1 | _ when isNull y-> // If x is not null and y is null, x is greater. 1 | _ -> // If x is not null and y is not null, compare the lengths of the two strings. let retval = x.Length.CompareTo y.Length if retval <> 0 then // If the strings are not of equal length, the longer string is greater. retval else // If the strings are of equal length, sort them with ordinary string comparison. x.CompareTo y let display list = printfn "" for s in list do if isNull s then printfn "(null)" else printfn $"\"%s{s}\"" let dinosaurs = ResizeArray() dinosaurs.Add "Pachycephalosaurus" dinosaurs.Add "Amargasaurus" dinosaurs.Add "" dinosaurs.Add null dinosaurs.Add "Mamenchisaurus" dinosaurs.Add "Deinonychus" display dinosaurs printfn "\nSort with generic Comparison<string> delegate:" dinosaurs.Sort 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" Imports System.Collections.Generic Public Class Example Private Shared Function CompareDinosByLength( _ ByVal x As String, ByVal y As String) As Integer If x Is Nothing Then If y Is Nothing Then ' If x is Nothing and y is Nothing, they're ' equal. Return 0 Else ' If x is Nothing and y is not Nothing, y ' is greater. Return -1 End If Else ' If x is not Nothing... ' If y Is Nothing Then ' ...and y is Nothing, x is greater. Return 1 Else ' ...and y is not Nothing, compare the ' lengths of the two strings. ' Dim retval As Integer = _ x.Length.CompareTo(y.Length) If retval <> 0 Then ' 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) End If End If End If End Function Public Shared Sub Main() Dim dinosaurs As New List(Of String) dinosaurs.Add("Pachycephalosaurus") dinosaurs.Add("Amargasaurus") dinosaurs.Add("") dinosaurs.Add(Nothing) dinosaurs.Add("Mamenchisaurus") dinosaurs.Add("Deinonychus") Display(dinosaurs) Console.WriteLine(vbLf & "Sort with generic Comparison(Of String) delegate:") dinosaurs.Sort(AddressOf CompareDinosByLength) Display(dinosaurs) End Sub Private Shared Sub Display(ByVal lis As List(Of String)) Console.WriteLine() For Each s As String In lis If s Is Nothing Then Console.WriteLine("(Nothing)") Else Console.WriteLine("""{0}""", s) End If Next End Sub End Class ' This code example produces the following output: ' '"Pachycephalosaurus" '"Amargasaurus" '"" '(Nothing) '"Mamenchisaurus" '"Deinonychus" ' 'Sort with generic Comparison(Of String) delegate: ' '(Nothing) '"" '"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 open System type CityInfo = { City: string Country: string Population: int } static member CompareByName city1 city2 = String.Compare(city1.City, city2.City) static member CompareByPopulation city1 city2 = city1.Population.CompareTo city2.Population static member CompareByNames city1 city2 = String.Compare(city1.Country + city1.City, city2.Country + city2.City) let display cities = printfn $"""{"City",-20} {"Country",-25} {"Population",10}""" for city in cities do printfn $"{city.City,-20} {city.Country,-25} {city.Population,10:N0}" printfn "" let NYC = { City = "New York City"; Country = "United States of America"; Population = 8175133 } let Det = { City = "Detroit"; Country = "United States of America"; Population = 713777 } let Paris = { City = "Paris"; Country = "France"; Population = 2193031 } let cities = [| NYC; Det; Paris |] // Display ordered array. display cities // Sort array by city name. Array.Sort(cities, CityInfo.CompareByName) display cities // Sort array by population. Array.Sort(cities, CityInfo.CompareByPopulation); display cities // Sort array by country + city name. Array.Sort(cities, CityInfo.CompareByNames); display cities // 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 Public Class CityInfo Dim cityName As String Dim countryName As String Dim pop2010 As Integer Public Sub New(name As String, country As String, pop2010 As Integer) Me.cityName = name Me.countryName = country Me.pop2010 = pop2010 End Sub Public ReadOnly Property City As String Get Return Me.cityName End Get End Property Public ReadOnly Property Country As String Get Return Me.countryName End Get End Property Public ReadOnly Property Population As Integer Get Return Me.pop2010 End Get End Property Public Shared Function CompareByName(city1 As CityInfo, city2 As CityInfo) As Integer Return String.Compare(city1.City, city2.City) End Function Public Shared Function CompareByPopulation(city1 As CityInfo, city2 As CityInfo) As Integer Return city1.Population.CompareTo(city2.Population) End Function Public Shared Function CompareByNames(city1 As CityInfo, city2 As CityInfo) As Integer Return String.Compare(city1.Country + city1.City, city2.Country + city2.City) End Function End Class Module Example Public Sub Main() Dim NYC As New CityInfo("New York City", "United States of America", 8175133) Dim Det As New CityInfo("Detroit", "United States of America", 713777) Dim Paris As New CityInfo("Paris", "France", 2193031) Dim cities As CityInfo() = { NYC, Det, Paris } ' Display ordered array. DisplayArray(cities) ' Sort array by city name. Array.Sort(cities, AddressOf CityInfo.CompareByName) DisplayArray(cities) ' Sort array by population. Array.Sort(cities, AddressOf CityInfo.CompareByPopulation) DisplayArray(cities) ' Sort array by country + city name. Array.Sort(cities, AddressOf CityInfo.CompareByNames) DisplayArray(cities) End Sub Private Sub DisplayArray(cities() As CityInfo) Console.WriteLine("{0,-20} {1,-25} {2,10}", "City", "Country/Region", "Population") For Each city In cities Console.WriteLine("{0,-20} {1,-25} {2,10:N0}", city.City, city.Country, city.Population) Next Console.WriteLine() End Sub End Module ' The example displays the following output: ' City Country/Region 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/Region 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/Region 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/Region Population ' Paris France 2,193,031 ' Detroit United States of America 713,777 ' New York City United States of America 8,175,133

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.