C# LINQ NET 3.5 SP1：使用 LINQ 按两个字段分组，并为组的所有成员分配一个相关的唯一 ID（整数）

Question

我有一个源列表，其中每个项目都是一个具有公共属性的类。

物品类别：

public class Item
{
   public DateTime Date
   {
     get;
     set;
   }
   public string ProviderID
   {
     get;
     set;
   }    
   public List<AnotherClass> listOfitems
   {
     get;       
     set;
   }
   public byte[] Img
   {
     get;
     set;
   }
   // Other properties

   public long GroupID
   {
     get;
     set;
   }
}

来源列表例如：

List<Item> mySourceList;

所以想象一下 mySourceList 在开始时如下所示（此处以表格模式表示）：

Date        | ProviderID   |  BillID  | QuantityToPay  | State    | GroupID
01/07/2015    9080AB          6453300      2100           Pending      0
20/01/2014    1080ZX          1200000      1500           Pending      0
01/07/2015    9080AB          6454000      1000           Pending      0
23/11/2016    6080AB          7853300     15000           Pending      0
02/10/2015    9080AB          6454100      2000           Pending      0
01/01/2017    2161DV          9200000       500           Pending      0
20/05/2017    8733ZZ          9800153     60000           Pending      0
01/01/2017    2161DV          9200001     21000           Pending      0
01/01/2017    2161DV          9200002     51700           Pending      0
20/05/2017    8733ZZ          9800154     90000           Pending      0
20/04/2017    8733ZZ          9800102     25000           Pending      0
20/06/2017    8733ZZ          9800200     90000           Pending      0
20/04/2017    8733ZZ          9800103     50000           Pending      0

现在使用 LINQ，我想获取另一个列表 myDestList，它先按 Provider 分组，然后按日期字段分组，还按 Provider 分组，然后按日期排序。 此外，我想为包含超过 1 行的每个组（Date，ProviderID）分配一个相关编号（GroupID）（对于同一组的所有成员，该编号应该相同）。仅包含 1 行的组，此相关数将始终为 0。例如，在处理上面的列表后，我想获得下面的列表 myDestList：

Date        | ProviderID   |  BillID  | QuantityToPay  | State    | GroupID
20/01/2014    1080ZX          1200000      1500           Pending      0
01/01/2017    2161DV          9200000       500           Pending      1
01/01/2017    2161DV          9200001     21000           Pending      1
01/01/2017    2161DV          9200002     51700           Pending      1
23/11/2016    6110FB          7853300     15000           Pending      0
20/04/2017    8733ZZ          9800102     25000           Pending      2
20/04/2017    8733ZZ          9800103     50000           Pending      2
20/05/2017    8733ZZ          9800153     60000           Pending      3
20/05/2017    8733ZZ          9800154     90000           Pending      3
20/06/2017    8733ZZ          9800200     90000           Pending      0
01/07/2015    9080AB          6453300      2100           Pending      4
01/07/2015    9080AB          6454000      1000           Pending      4
02/10/2015    9080AB          6454100      2000           Pending      0

我在下面尝试（没有为每个组分配相关编号，因为我不知道该怎么做）：

List<Item> myDestList = mySourceList.GroupBy(x => new { x.ProviderID, x.Date }).Select(grp => grp.ToList<Item>()).ToList<Item>();

如何使用 LINQ 做到这一点？

尝试#1：

最后我做了以下：

    var grp = mySourceList .GroupBy(e => new { e.ProviderID, e.Date });

    int groupId = 1;
    foreach (var group in grp)
    {
        int id = group.Count() > 1 ? groupId++ : 0;

        // Loop through each item within group
        foreach (var item in group)
            item.GroupID = id;
    }

Answer 1

我假设您不想就地更新您的项目，而只需要生成新项目。我也不太清楚其他属性或“AnotherClass”在哪里出现。所以这里有一些代码，它采用了 Item 的缩减版本（只是 Date、ProviderID 和 GroupID）并为您提供所需的结果。
请注意，分配的 GroupID 不是连续的。

缩减类：

public class Item
{
    public DateTime Date { get; set; }
    public string ProviderID { get; set; }
    public long GroupID { get ; set ; }
}

填充“mySourceList”（诚然有点粗糙，准备日期解析）：

        List<Item> mySourceList = new List<Item>()
        {
            new Item {Date=DateTime.Parse("01/07/2015"), ProviderID = "9080AB", GroupID = 0 },
            new Item {Date=DateTime.Parse("20/01/2014"), ProviderID = "1080ZX", GroupID = 0 },
            new Item {Date=DateTime.Parse("01/07/2015"), ProviderID = "9080AB", GroupID = 0 },
            new Item {Date=DateTime.Parse("23/11/2016"), ProviderID = "6080AB", GroupID = 0 },
            new Item {Date=DateTime.Parse("02/10/2015"), ProviderID = "9080AB", GroupID = 0 },
            new Item {Date=DateTime.Parse("01/01/2017"), ProviderID = "2161DV", GroupID = 0 },
            new Item {Date=DateTime.Parse("20/05/2017"), ProviderID = "8733ZZ", GroupID = 0 },
            new Item {Date=DateTime.Parse("01/01/2017"), ProviderID = "2161DV", GroupID = 0 },
            new Item {Date=DateTime.Parse("01/01/2017"), ProviderID = "2161DV", GroupID = 0 },
            new Item {Date=DateTime.Parse("20/05/2017"), ProviderID = "8733ZZ", GroupID = 0 },
            new Item {Date=DateTime.Parse("20/04/2017"), ProviderID = "8733ZZ", GroupID = 0 },
            new Item {Date=DateTime.Parse("20/06/2017"), ProviderID = "8733ZZ", GroupID = 0 },
            new Item {Date=DateTime.Parse("20/04/2017"), ProviderID = "8733ZZ", GroupID = 0 },
        };

Linq：

        var myDestList = mySourceList.OrderBy(i => i.Date).ThenBy(i => i.ProviderID)
            .GroupBy(x => new {x.ProviderID, x.Date})
            .Select((grp, idx) => new {GroupId = idx+1, GroupCount = grp.Count(), Items = grp})
            .SelectMany(newgrp => newgrp.Items.DefaultIfEmpty(), (g, i) => new { Date=i.Date, ProviderID = i.ProviderID, GroupID = (g.GroupCount == 1 ? 0 : g.GroupId)})
            .OrderBy(i => i.Date).ThenBy(i=>i.ProviderID)
            .ToList();

结果：

{ Date = 20/01/2014 00:00:00, ProviderID = 1080ZX, GroupID = 0 }
{ Date = 01/07/2015 00:00:00, ProviderID = 9080AB, GroupID = 2 }
{ Date = 01/07/2015 00:00:00, ProviderID = 9080AB, GroupID = 2 }
{ Date = 02/10/2015 00:00:00, ProviderID = 9080AB, GroupID = 0 }
{ Date = 23/11/2016 00:00:00, ProviderID = 6080AB, GroupID = 0 }
{ Date = 01/01/2017 00:00:00, ProviderID = 2161DV, GroupID = 5 }
{ Date = 01/01/2017 00:00:00, ProviderID = 2161DV, GroupID = 5 }
{ Date = 01/01/2017 00:00:00, ProviderID = 2161DV, GroupID = 5 }
{ Date = 20/04/2017 00:00:00, ProviderID = 8733ZZ, GroupID = 6 }
{ Date = 20/04/2017 00:00:00, ProviderID = 8733ZZ, GroupID = 6 }
{ Date = 20/05/2017 00:00:00, ProviderID = 8733ZZ, GroupID = 7 }
{ Date = 20/05/2017 00:00:00, ProviderID = 8733ZZ, GroupID = 7 }
{ Date = 20/06/2017 00:00:00, ProviderID = 8733ZZ, GroupID = 0 }