c# - LINQ GroupBy 和 Select 在不同的属性上

Question

如果我有以下收藏：

var foos = new List<Foo>
{
    new Foo{ Name = "A", Value = 1 },
    new Foo{ Name = "B", Value = 1 },
    new Foo{ Name = "B", Value = 2 },
    new Foo{ Name = "C", Value = 1 },
};

我想结束：

A-1
B-2
C-1

在重复“B”的情况下，我想在哪里选择具有最高值的“B”？

就像是：

var filteredFoos = foos.GroupBy(x => x.Name).Select_Duplicate_With_Highest_Value

Answer 1

var filteredFoos = 
    foos.GroupBy(x => x.Name)
        .Select(x => new { Name = x.Key, Value = x.Max(f => f.Value) });

Answer 2

var query = from p in foos
            group p by p.Name into g
            select new
            {
                Name = g.Key,
                Value = g.Max(a => a.Value)
            };

Answer 3

试试这个查询：

var filteredFoos = foos.GroupBy(x => x.Name)
                       .Select(p => new { p.Key, p.Max(x => x.Value) });

Answer 4

对于超过 2 列的任何人：

var subquery = from p in foos
            group p by p.Name into g
            select new
            {
                Name = g.Key,
                Value = g.Max(a => a.Value)
            };
var query = from f in foos
            join s in subquery 
              on f.Name equals s.Name
            where f.Value == s.Value
            select f;

如果这违反 SQL，请确保 Name 是一个原语。