如何从Person对象列表中提取每个TeamNumber对应的首个成员

需求很明确：从给定的Person对象列表中，按TeamNumber分组后提取每组的第一个元素，生成仅包含各团队首个成员的精简列表。

先确认Person类定义 #

public class Person
{
    public int TeamNumber { get; set; }
    public string Name { get; set; }
}

原始完整列表示例 #

List<Person> list = new List<Person>()
{
    new Person(){TeamNumber = 1, Name = "Peter"},
    new Person(){TeamNumber = 1, Name = "Klaus"},
    new Person(){TeamNumber = 1, Name = "Maria"},
    new Person(){TeamNumber = 1, Name = "Gerda"},
    new Person(){TeamNumber = 2, Name = "Ralf"},
    new Person(){TeamNumber = 2, Name = "Oskar"},
    new Person(){TeamNumber = 2, Name = "Anna"},
    new Person(){TeamNumber = 3, Name = "Hannah"},
    new Person(){TeamNumber = 3, Name = "Susi"},
    new Person(){TeamNumber = 4, Name = "Ida"}
};

实现方法 #

方法一：使用GroupBy + First（兼容所有.NET版本）

通过GroupBy按TeamNumber分组，再对每个分组取第一个元素：

var firstMembersByTeam = list
    .GroupBy(person => person.TeamNumber)
    .Select(group => group.First())
    .ToList();

方法二：使用DistinctBy（.NET 6及以上版本可用）

.NET 6新增的DistinctBy方法可以直接按指定键去重，保留首次出现的元素，代码更简洁：

var firstMembersByTeam = list.DistinctBy(person => person.TeamNumber).ToList();

验证结果 #

遍历输出结果，会得到你期望的精简列表：

• TeamNumber = 1, Name = "Peter"
• TeamNumber = 2, Name = "Ralf"
• TeamNumber = 3, Name = "Hannah"
• TeamNumber = 4, Name = "Ida"

内容的提问来源于stack exchange，提问作者Frank Mehlhop