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准备要使用的List，用于分组（GroupBy）：
List<Person> personList = new List<Person>
{
new Person
{
Name = "P1", Age = 18, Gender = "Male"
},
new Person
{
Name = "P2", Age = 19, Gender = "Male",
},
new Person
{
Name = "P2", Age = 17,Gender = "Female",
}
};
最常用的方式：
var groups = personList.GroupBy(p => p.Gender, p => p.Name);
foreach (var group in groups)
{
Console.WriteLine(group.Key.ToString());
foreach (var name in group)
{
Console.WriteLine($"\t{name}");
}
}
输出结果：
Male
P1
P2
Female
P3
可见group本视是一个集合，当里面的元素只有1个的时候，你还是得以foreach的方式取得name，具体实例见：
关于PCRArenaRecorder&Analyzer的概率分析相关逻辑代码
这里面已经FirstOrDefault()出来了，但还是得foreach，不然你只能得到key，得不到key所对用的内容。
参考文档：
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