#region linq to object

List<People> peopleList = new List<People>();

peopleList.Add(new People { UserName = "zzl", Email = "" });

peopleList.Add(new People { UserName = "zzl", Email = "" });

peopleList.Add(new People { UserName = "lr", Email = "" });

peopleList.Add(new People { UserName = "lr", Email = "" });

Console.WriteLine("用扩展方法可以过滤某个字段，然后把当前实体输出");

peopleList.DistinctBy(i => new { i.UserName }).ToList().ForEach(i => Console.WriteLine(i.UserName + i.Email));

Console.WriteLine("默认方法，集合中有多个字段，当所有字段发生重复时，distinct生效，这与SQLSERVER相同");

peopleList.Select(i => new { UserName = i.UserName, Email = i.Email }).OrderByDescending(k => k.Email).Distinct().ToList().ForEach(i => Console.WriteLine(i.UserName + i.Email));

Console.WriteLine("集合中有一个字段，将这个字段重复的过滤，并输出这个字段");

peopleList.Select(i => new { i.UserName }).Distinct().ToList().ForEach(i => Console.WriteLine(i.UserName));

#endregion

public static class EnumerableExtensions

{

　　public static IEnumerable<TSource> DistinctBy<TSource, Tkey>(this IEnumerable<TSource> source, Func<TSource, Tkey> keySelector)

　　　　{

　　　　　　HashSet<Tkey> hashSet = new HashSet<Tkey>();

　　　　　　foreach (TSource item in source)

　　　　　　{

　　　　　　　　if (hashSet.Add(keySelector(item)))

　　　　　　　　{

　　　　　　　　　　yield return item;

　　　　　　　　}

　　　　　　}

　　　　　}

}