Question

我很难创建针对通用List myList的工作Group By和Sort By子句。 myList有一个属性'Settings'列表，它本身包含每个企业的'子'属性列表。

我希望按行业和每个行业进行分组，按商家名称排序。我的意图是：

string groupSetting = "Industry";
sortSetting = "BusinessName";
myList.GroupBy(p => p.Settings.Find(s => s.Name == groupSetting)).OrderBy(p => p.Settings.Find(t => t.Name == sortSetting));

但是我收到错误： ' System.Linq.IGrouping不包含Settings的定义，也没有扩展方法可以找到接受System.Linq.Igrouping类型的第一个参数的设置.... '表示我无法调用该命令没有经过一些改造或额外处理的条款。

我已经尝试过各种各样的事情来解决这个问题并让它发挥作用，但我错过了一些东西。任何帮助表示赞赏

Answer 1

您的问题是GroupBy没有返回单个设置列表，它返回“列表列表”。这是您所看到的IGrouping。

您需要遍历IGrouping中的每个组，对该组进行排序，然后迭代组中的每个项目。观察：

public static void Main( string[] args )
{
    var groupSetting = "Industry";

    // step 1: group the data. Note this doesn't actually create copies of the data as
    // it's all lazy loaded
    // BEWARE. If a company doesn't have the "Industry" setting, this will throw an exception
    var grouped = companies.GroupBy(c => c.Settings.First(s => s.Name == groupSetting).Value);
    foreach( var group in grouped )
    {
        Console.WriteLine(group.Key);// this is the Value that came out of the GroupBy

        // Note how we have to do the ordering within each individual group. 
        // It doesn't make sense to try group them in one hit like in your question
        foreach( var item in group.OrderBy(bus => bus.Name) )
            Console.WriteLine(" - " + item.Name);
    }
}

为清晰起见，提供了数据结构：

struct Setting { public string Name; public string Value; }
struct Business { public string Name; public IEnumerable<Setting> Settings; }

static IEnumerable<Business> companies = new[]{
    new Business{ Name = "XYZ Inc.", Settings = new[]{ 
        new Setting{ Name="Age", Value="27"},
        new Setting{ Name="Industry", Value="IT"}
    }},
    new Business{ Name = "Programmers++", Settings = new[]{ 
        new Setting{ Name="Age", Value="27"},
        new Setting{ Name="Industry", Value="IT"}
    }},
    new Business{ Name = "Jeff's Luxury Salmon", Settings = new[]{ 
        new Setting{ Name="Age", Value="63"},
        new Setting{ Name="Industry", Value="Sports"}
    }},
    new Business{ Name = "Bank of Khazakstan", Settings = new[]{ 
        new Setting{ Name="Age", Value="30"},
        new Setting{ Name="Industry", Value="Finance"}
    }},
};

这会产生以下输出：复制/粘贴代码并运行它并使用它

IT
 - Programmers++
 - XYZ Inc.
Sports
 - Jeff's Luxury Salmon
Finance
 - Bank of Khazakstan

将LINQ应用于对象分组依据和排序依据通用List <t>（C＃）</t>

1 个答案: