从自定义实体列表创建字典的最佳LINQ方法

Question

我有一个DeleteByVendor对象列表。它有两个业务实体-供应商和价格页..一个价格页可以有多个供应商..一个供应商可以出现在多个价格页中。

我们需要创建一个字典，其中将包含每个价格页以及该价格页中存在的（ distinct ）供应商数量。 一个价格页在该词典中只能出现一次。

我们如何使用LINQ chain method来做到这一点？

注意：对于“ P3”，计数应为1（尽管有重复的记录）

class Program
{
    static void Main(string[] args)
    {

        List<DeleteByVendor> vendorsForPages = new List<DeleteByVendor>();

        DeleteByVendor item1 = new DeleteByVendor() { VendorID = "V1", VendorName = "Vendor1", PricePage = "P1", Description = "Description1" };
        DeleteByVendor item2 = new DeleteByVendor() { VendorID = "V2", VendorName = "Vendor2", PricePage = "P1", Description = "Description1" };
        DeleteByVendor item3 = new DeleteByVendor() { VendorID = "V1", VendorName = "Vendor1", PricePage = "P2", Description = "Description2" };
        DeleteByVendor item4 = new DeleteByVendor() { VendorID = "V1", VendorName = "Vendor1", PricePage = "P3", Description = "Description3" };
        //Duplicate
        DeleteByVendor item5 = new DeleteByVendor() { VendorID = "V1", VendorName = "Vendor1", PricePage = "P3", Description = "Description3" };

        Dictionary<string, int> costPageVendorsCount = new Dictionary<string, int>();

    }
}

public class DeleteByVendor
{
    public string VendorID { get; set; }
    public string VendorName { get; set; }
    public string PricePage { get; set; }
    public string Description { get; set; }
}

Answer 1

首先使用GroupBy方法按PricePage对列表进行PricePage 。 然后使用ToDictionary获取字典。

var results = vendorsForPages.GroupBy(v => v.PricePage)
                             .ToDictionary(g => g.Key,
                                           g => g.Select(x => x.VendorID)
                                                 .Distinct()
                                                 .Count());

Answer 2

您可以按PricePage分组，然后按VendorId ：

var costPageVendorsCount = vendorsForPages.GroupBy(v => v.PricePage)
                                          .ToDictionary(g => g.Key, 
                                                        g => g.GroupBy(gg => gg.VendorID)
                                                              .Count()
                                                       );