Metodo di estensione per implementare Intersect

Scritto da  Alessandro Mostarda il mercoledì 22 dicembre 2010  •  Linguaggio: C#,VB   • Livello: 200


Il seguente metodo di estensione implementa la funzione Intersect tra due liste con una funzione di confronto definita tramite lambda expression. Il metodo ritorna solo le istanze della collection a cui è applicato il metodo stesso.

Tale metodo può essere paragonato alla JOIN di LINQ, con l'unica differenza che non è possibile selezionare il tipo di ritorno.

C#

public static IEnumerable<T> Intersect<T,C>(this IEnumerable<T> source, IEnumerable<C> target, Func<T, C, bool> compareCriteria)

{

    return source.Where(x => target.Any(y => compareCriteria(x, y)));

}

 

VB.NET

Imports System.Runtime.CompilerServices

Public Module Extension



    <Extension()> _

    Public Function Intersect(Of T, C)(ByVal source As IEnumerable(Of T), _

                                        ByVal target As IEnumerable(Of C), _

                                        ByVal compareCriteria As Func(Of T, C, Boolean)) As IEnumerable(Of T)

        Return source.Where(Function(x) target.Any(Function(y) compareCriteria(x, y)))

    End Function



End Module

 

La sintassi per utilizzarli è la seguente:

C#

public void Main()

{

    List<Person> firstList = new List<Person>();

    firstList.Add(new Person {Name = "Antonio",

                              Surname = "Verdi",

                              DateOfBirth = new System.DateTime(1975, 7, 22)

                              });

    firstList.Add(new Person {Name = "Mario",

                              Surname = "Rossi",

                              DateOfBirth = new System.DateTime(1956, 3, 14)

                              });

    firstList.Add(new Person {Name = "Giuseppe",

                              Surname = "Bianchi",

                              DateOfBirth = new System.DateTime(1985, 11, 25)

                              });



    List<Person> secondList = new List<Person>();

    secondList.Add(new Person {Name = "Mario",

                               Surname = "Verdi",

                               DateOfBirth = new System.DateTime(1975, 7, 22)

                               });

    secondList.Add(new Person {Name = "Mario",

                               Surname = "Rossi",

                               DateOfBirth = new System.DateTime(1989, 2, 4)

                               });

    secondList.Add(new Person {Name = "Giuseppe",

                               Surname = "Verdi",

                               DateOfBirth = new System.DateTime(1985, 11, 14)

                               });



    var matchBySurname = firstList.Intersect(secondList, (x, y) => x.Surname == y.Surname);

    var matchByName = firstList.Intersect(secondList, (x, y) => x.Name == y.Name);

    var matchByNameAndSurname = firstList.Intersect(secondList, (x, y) => x.Name == y.Name && x.Surname == y.Surname);

    var matchByYear = firstList.Intersect(secondList, (x, y) => x.DateOfBirth.Year == y.DateOfBirth.Year);

}



public class Person

{

    public string Name { get; set; }

    public string Surname { get; set; }

    public DateTime DateOfBirth { get; set; }

}

 

VB.NET

Sub Main()

    Dim firstList As New List(Of Person)

    firstList.Add(New Person With {.Name = "Antonio", _

                                   .Surname = "Verdi", _

                                   .DateOfBirth = New Date(1975, 7, 22)})

    firstList.Add(New Person With {.Name = "Mario", _

                                   .Surname = "Rossi", _

                                   .DateOfBirth = New Date(1956, 3, 14)})

    firstList.Add(New Person With {.Name = "Giuseppe", _

                                   .Surname = "Bianchi", _

                                   .DateOfBirth = New Date(1985, 11, 25)})

  

    Dim secondList As New List(Of Person)

    secondList.Add(New Person With {.Name = "Mario", _

                                    .Surname = "Verdi", _

                                    .DateOfBirth = New Date(1975, 7, 22)})

    secondList.Add(New Person With {.Name = "Mario", _

                                    .Surname = "Rossi", _

                                    .DateOfBirth = New Date(1989, 2, 4)})

    secondList.Add(New Person With {.Name = "Giuseppe", _

                                    .Surname = "Verdi", _

                                    .DateOfBirth = New Date(1985, 11, 14)})

  

    Dim matchBySurname = firstList.Intersect(secondList, Function(x, y) x.Surname = y.Surname)

    Dim matchByName = firstList.Intersect(secondList, Function(x, y) x.Name = y.Name)

    Dim matchByNameAndSurname = firstList.Intersect(secondList, Function(x, y) x.Name = y.Name AndAlso x.Surname = y.Surname)

    Dim matchByYear = firstList.Intersect(secondList, Function(x, y) x.DateOfBirth.Year = y.DateOfBirth.Year)

  

End Sub



Public Class Person

    Public Property Name As String

    Public Property Surname As String

    Public Property DateOfBirth As DateTime

End Class


Tags: Linq

 
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