NET[C#]LINQ中如何按实体的某个属性去重后返回不重复的集合？

问题描述

比如有如下实体集合：

Person1: Id=1, Name="Test1"
Person2: Id=1, Name="Test1"
Person3: Id=2, Name="Test2"

如何使用LINQ按 Person.Id 去重，返回的集合只包含 Person1 和 Person3 ？

方案一

创建一个静态扩展类：

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

调用方法：

var query = people.DistinctBy(p => p.Id);

如果需要按多个属性去重，则可以使用匿名对象，如：

var query = people.DistinctBy(p => new { p.Id, p.Name });

方案二

List<Person> distinctPeople = allPeople
  .GroupBy(p => p.PersonId)
  .Select(g => g.First())
  .ToList();

多属性去重：

List<Person> distinctPeople = allPeople
  .GroupBy(p => new {p.PersonId, p.FavoriteColor} )
  .Select(g => g.First())
  .ToList();

方案三

var uniquePeople = from p in people
                   group p by new {p.ID} //or group by new {p.ID, p.Name, p.Whatever}
                   into mygroup
                   select mygroup.FirstOrDefault();

方案四

Persons.ToLookup(p => p.Id).Select(coll => coll.First());

方案五

var result = people.Where(p => !people.Any(q => (p != q && p.Id == q.Id)));