C# 林奇 : Get items with max price

Question

我有一个对象列表:

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)列表的最佳方法是什么。结果列表需要:

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

好吧，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();
                };

如果您需要 LINQ to SQL(其中您不能使用语句 lambda)，您可以使用:

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，Where 的每次迭代效率较低，它将重新计算最高价格。

如果您希望能够返回多个具有给定名称且价格相同的商品，请调整 .First() 部分。

在 LINQ to Objects 中，您还可以使用 MoreLINQ的 MaxBy方法:

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