C# Enumerable GroupJoin(IEnumerable, IEnumerable, Func, Func, Func, TResult>)
Description
Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys.
Syntax
public static IEnumerable<TResult> GroupJoin<TOuter, TInner, TKey, TResult>(
this IEnumerable<TOuter> outer,
IEnumerable<TInner> inner,//w ww .j a v a 2 s.c o m
Func<TOuter, TKey> outerKeySelector,
Func<TInner, TKey> innerKeySelector,
Func<TOuter, IEnumerable<TInner>, TResult> resultSelector
)
Parameters
TOuter- The type of the elements of the first sequence.TInner- The type of the elements of the second sequence.TKey- The type of the keys returned by the key selector functions.TResult- The type of the result elements.outer- The first sequence to join.inner- The sequence to join to the first sequence.outerKeySelector- A function to extract the join key from each element of the first sequence.innerKeySelector- A function to extract the join key from each element of the second sequence.resultSelector- A function to create a result element from an element from the first sequence and a collection of matching elements from the second sequence.
Example
The following code example demonstrates how to use GroupJoin to perform a grouped join on two sequences.
/*from w w w.j a v a 2 s.co m*/
using System;
using System.Linq;
using System.Collections.Generic;
public class MainClass{
public static void Main(String[] argv){
Person magnus = new Person { Name = "A" };
Person terry = new Person { Name = "B" };
Person charlotte = new Person { Name = "C" };
Pet petA = new Pet { Name = "D", Owner = terry };
Pet petB = new Pet { Name = "E", Owner = terry };
Pet petC = new Pet { Name = "F", Owner = charlotte };
Pet petD = new Pet { Name = "G", Owner = magnus };
List<Person> people = new List<Person> { magnus, terry, charlotte };
List<Pet> pets = new List<Pet> { petA, petB, petC, petD };
var query = people.GroupJoin(pets,
person => person,
pet => pet.Owner,
(person, petCollection) =>
new
{
OwnerName = person.Name,
Pets = petCollection.Select(pet => pet.Name)
});
foreach (var obj in query)
{
Console.WriteLine("{0}:", obj.OwnerName);
foreach (string pet in obj.Pets)
{
Console.WriteLine(" {0}", pet);
}
}
}
}
class Person{
public string Name { get; set; }
}
class Pet {
public string Name { get; set; }
public Person Owner { get; set; }
}