C# GroupBy - 创建多个分组级别

Question

给定以下类:

public class Transaction
{
    public string Category { get; set; }
    public string Form { get; set; }
}

如何获得一组按 Category 和 Form 分组的交易？

基本上我希望它像这样输出:

Category 1
    Form 1
        Transaction1
        Transaction2
        Transaction3
        ...
    Form 2
        Transaction1
        Transaction2
        Transaction3
        ...
Category 2
    Form 1
        Transaction1
        Transaction2
        Transaction3
        ...
    Form 2
        Transaction1
        Transaction2
        Transaction3
        ...

Answer 1

这是一个使用嵌套 foreach 循环的示例，我不确定您如何在单个 linq 语句字符串中执行此操作，也许有很多 selectmanys？

var transactions = new[]{
    new{Category = "1", Form = "1", Title = "Trans1" },
    new{Category = "1", Form = "1", Title = "Trans2" },
    new{Category = "1", Form = "1", Title = "Trans3" },
    new{Category = "1", Form = "2", Title = "Trans1" },
    new{Category = "1", Form = "2", Title = "Trans2" },
    new{Category = "1", Form = "2", Title = "Trans3" },
    new{Category = "2", Form = "1", Title = "Trans1" },
    new{Category = "2", Form = "1", Title = "Trans2" },
    new{Category = "2", Form = "1", Title = "Trans3" },
    new{Category = "1", Form = "3", Title = "Trans1" },
    new{Category = "1", Form = "3", Title = "Trans2" },
    new{Category = "1", Form = "3", Title = "Trans3" },
};

foreach(var byCategory in transactions.GroupBy(x => x.Category))
{
    Console.WriteLine(byCategory.Key);
    foreach(var byForm in byCategory.GroupBy(x => x.Form))
    {
        Console.WriteLine("\t" + byForm.Key);
        foreach(var trans in byForm)
        {
            Console.WriteLine("\t\t" + trans.Title);
        }
    }
}

只是因为我很好奇我想出以下内容会是什么样子，你不应该在生产代码中使用它，因为它很荒谬(如果你有这样的数据结构，它应该被分解成类似的东西Dictionary<CategoryName, FormGroup> 或有意义类型的东西)

Dictionary<string, Dictionary<string, List<string>>> tooManyDictionaries = transactions
        .GroupBy(x => x.Category)
        .ToDictionary(
            catGroup => catGroup.Key,
            catGroup => catGroup
                .GroupBy(x => x.Form)
                .ToDictionary(
                    formGroup => formGroup.Key,
                    formGroup => formGroup.Select(x => x.Title).ToList()));