Question

我有一个我的对象列表：

class MyObj
{
    public String Title { get; set; }
    public Decimal Price { get; set; }
    public String OtherData { get; set; }
}

var list = new List<MyObj> {
 new MyObj { Title = "AAA", Price = 20, OtherData = "Z1" },
 new MyObj { Title = "BBB", Price = 20, OtherData = "Z2" },
 new MyObj { Title = "AAA", Price = 30, OtherData = "Z5" },
 new MyObj { Title = "BBB", Price = 10, OtherData = "Z10" },
 new MyObj { Title = "CCC", Price = 99, OtherData = "ZZ" }
};

获取具有唯一标题和MAX（价格）的列表的最佳方法是什么。结果列表必须是：

var ret = new List<MyObj> {
 new MyObj { Title = "BBB", Price = 20, OtherData = "Z2" },
 new MyObj { Title = "AAA", Price = 30, OtherData = "Z5" },
 new MyObj { Title = "CCC", Price = 99, OtherData = "ZZ" }
};

Answer 1

嗯，你可以这样做：

var query = list.GroupBy(x => x.Title)
                .Select(group =>
                {
                    decimal maxPrice = group.Max(x => x.Price);
                    return group.Where(x => x.Price == maxPrice)
                                .First();
                };

如果你需要LINQ to SQL（你不能使用语句lambdas），你可以使用：

var query = list.GroupBy(x => x.Title)
       .Select(group => group.Where(x => x.Price == group.Max(y => y.Price))
                             .First());

请注意，在LINQ to Objects中效率低于Where的每次迭代时，它会重新计算最高价格。

如果您希望能够返回多个具有给定名称的项目（如果它们具有相同的价格），请调整.First()部分。

在LINQ to Objects中你也可以使用MoreLINQ的MaxBy方法：

var query = list.GroupBy(x => x.Title)
                .Select(group => group.MaxBy(x => x.Price));

Answer 2

var ret = list.GroupBy(x => x.Title)
              .Select(g => g.Aggregate((a, x) => (x.Price > a.Price) ? x : a));

（如果您需要结果为List<T>而非IEnumerable<T>序列，则只需将ToList电话标记到最后。）

Answer 3

var ret = list.OrderByDescending(x => x.Price).GroupBy(x => x.Title).Select(@group => @group.ElementAt(0)).ToList();

这应该这样做。

Answer 4

想提一下

var query = list.GroupBy(x => x.Title)
       .Select(group => group.Where(x => x.Price == group.Max(y => y.Price))
       .First());

应该是

var query = list.GroupBy(x => x.Title)
       .First(group => group.Where(x => x.Price == group.Max(y => y.Price)));

我喜欢Richard解决最大n组/ 问题。

var query = list
    .OrderByDescending(o => o.Price)    //set ordering
    .GroupBy(o => o.Title)              //set group by
    .Select(o => o.First());            //take the max element

但是需要稍加修改

var query = list
    .OrderByDescending(o => o.Price)                       //set ordering
    .GroupBy(o => o.Title)                                 //set group by
    .Select(o => o.Where(k => k.Price == o.First().Price)) //take max elements

C＃LINQ：获取最高价格的商品

4 个答案: