List<int> listA = new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8 };
List<int> listB = new List<int>() { 1, 2, 3, 4, 9 };

var resultUnionList= listA.Union(listB).ToList();

var resultIntersectList = listA.Intersect(listB);

var resultExceptList = listA.Except(listB);

    /// <summary>
    /// 学生类
    /// </summary>
    public class Student
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public string Sex { get; set; }
    }

            //LISTA
            List<Student> stuListA = new List<Student>();
            stuListA.Add(new Student
            {
                Name = "A1",
                Age = 10,
                Sex = "男"
            });
            stuListA.Add(new Student
            {
                Name = "A2",
                Age = 11,
                Sex = "男"
            });

            //LISTB
            List<Student> stuListB = new List<Student>();
            stuListB.Add(new Student
            {
                Name = "B1",
                Age = 10,
                Sex = "女"
            });
            stuListB.Add(new Student
            {
                Name = "B2",
                Age = 11,
                Sex = "男"
            });   

var result = stuListA.Union(stuListB).ToList();

var result = stuListA.Where(x => stuListB.Any(e => e.Name == x.Name)).ToList();

var result = stuListA.Where(x => stuListB.Any(e => e.Name == x.Name && e.Age == x.Age && e.Sex == x.Sex)).ToList();

var result = stuListA.Where(x =>! stuListB.Any(e => e.Name == x.Name)).ToList();

var result = stuListA.Where(x => !stuListB.Any(e => e.Name == x.Name && e.Age == x.Age && e.Sex == x.Sex)).ToList();

var list = (new[]{"1","2","3"}).ToList();
var newlist = list.Select<string,int>(x =>Convert.ToInt32(x));

List<int> 转List<string> 

List<int> list = new List<int>(new int[] { 1,2,3 } );
List<string> newList = list.ConvertAll<string>(x => x.ToString());

public class Test
{ 
     public int ID { get; set; }
     public string Name { get; set; }
}

public class TestMain
{
　　public static void TestMothod()
　　{
   　　List<Test> testList = new List<Test>();
      testList.Add(new Test { ID = 1, Name = "小名" });
      testList.Add(new Test { ID = 1, Name = "小红" });
      testList.Add(new Test { ID = 2, Name = "小名" });
      //通过使用默认的相等比较器对值进行比较返回序列中的非重复元素。
      List<Test> tempList = testList.Distinct<Test>().ToList();
   }
}

 public static class DistinctExtension
 {
    public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, System.Func<TSource, TKey> keySelector)
    {
        HashSet<TKey> seenKeys = new HashSet<TKey>();
        foreach (TSource element in source)
        {
            if (seenKeys.Add(keySelector(element)))
            {
                yield return element;
            }
        }
    }
 }

public class TestMain
{
　　public static void TestMothod()
   {
       List<Test> testList = new List<Test>();
       testList.Add(new Test { ID = 1, Name = "小名" });
       testList.Add(new Test { ID = 1, Name = "小红" });
       testList.Add(new Test { ID = 2, Name = "小名" });
       //根据某个字段排除重复项。
       List<Test> tempList = testList.DistinctBy(p => p.ID).ToList();
   }
}