c# - 连接两个 List，其中每个列表中的字段值相等

Question

class Person
{
    public String FirstName { get; set; }
    public String LastName { get; set; }

    public Person(String firstName String lastName)
    {
        FirstName = firstName 
        LastName = lastName;
    }
}

public static void Main()
{
    List<Person> males = new List<Person>();

    males.Add(new Person() {FirstName = "Fred", LastName = "Blogs"});
    males.Add(new Person() {FirstName = "John", LastName = "James"});
    males.Add(new Person() {FirstName = "Harry", LastName = "Adams"});
    males.Add(new Person() {FirstName = "Peter", LastName = "Blogs"});

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

    females.Add(new Person() {FirstName = "Mary", LastName = "Blogs"});
    females.Add(new Person() {FirstName = "Anne", LastName = "James"});
    females.Add(new Person() {FirstName = "Jane", LastName = "Doe"});

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

    results = males.Concat(females)...; // This is where I stumble ??
}

List<Person> results需要包含 males.LastName 所在的所有行和 females.LastName存在于两个列表中。

即List<Person> results应该包含...

    FirstName = "Fred", LastName = "Blogs"});
    FirstName = "John", LastName = "James"});
    FirstName = "Peter", LastName = "Blogs"});
    FirstName = "Mary", LastName = "Blogs"});
    FirstName = "Anne", LastName = "James"});

注意:Harry Adams 和 Jane Doe 应该被排除在外，因为他们的姓氏不在两个列表中。

(换句话说，如果我最喜欢的啤酒公司统治世界，我需要这样的东西:

`results = males.Concat(female).Where(males.LastName == female.LastName);`

它会弄清楚...啊!如果只是)

如有任何帮助，我们将不胜感激。

Answer 1

var result = males.Concat(females).Where(p => males.Any(x => p.LastName == x.LastName) && 
                                             females.Any(x => p.LastName == x.LastName))
                                 .ToList();

这是给出预期结果的完整代码:

[Test]
public void LINQTest()
{
     List<Person> males = new List<Person>();

     males.Add(new Person() { FirstName = "Fred", LastName = "Blogs" });
     males.Add(new Person() { FirstName = "John", LastName = "James" });
     males.Add(new Person() { FirstName = "Harry", LastName = "Adams" });
     males.Add(new Person() { FirstName = "Peter", LastName = "Blogs" });

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

     females.Add(new Person() { FirstName = "Mary", LastName = "Blogs" });
     females.Add(new Person() { FirstName = "Anne", LastName = "James" });
     females.Add(new Person() { FirstName = "Jane", LastName = "Doe" });

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

     var result = males.Concat(females).Where(p => males.Any(x => p.LastName == x.LastName) &&
                                                   females.Any(x => p.LastName == x.LastName))
                                       .ToList();

        Assert.AreEqual(result.Count, 5); // true
}

或者你可以像这样使用 Intersect 和 Contains，它可能会快得多。

 var names = males.Select(p => p.LastName)
                  .Intersect(females.Select(p => p.LastName))
                  .ToList();
var result = males.Concat(females)
                    .Where(p =>names.Contains(p.LastName))
                    .ToList();