由兩個參數分組和計數在linq中，考慮發生0

Question

我有一個對象objA的IQueriable<EntityA>類型，我想在C＃中使用lambda表示法進行查詢，按兩個參數（Status和WeekOfYear）進行分組，並計數objA中每個EntityA類型實體的出現。我想結果集計數爲0.

IQueriable<EntityA> objA= ... 

var group = objA.GroupBy(a => new { a.Status, a.WeekOfYear }) 
       .Select(a => new { a.Key.Status, a.Key.Week, Count = a.Count() }); 

上面的代碼是最接近我從我想要的。它返回IQueriable<int, int, int>，我可以很容易地插入到我的Excel表格中。但是當計數爲0時，我沒有在結果集中看到一個入口，然後填寫Excel工作表變得非常棘手。是否有可能獲得我需要的結果，還是我真的必須檢查所有對（如此不雅!!!）？

Answer 1

如果您使用Distinct()函數，則可以獲取所有狀態和所有WeekOfYear並檢查每個元組的計數。

代碼是這樣的，你可以在fiddle

using System; 
using System.Linq; 
using System.Collections.Generic; 

public class Program 
{ 
    public static void Main() 
    { 
     IQueryable<Entity> data = (new List<Entity>() { 
      new Entity { Status = "1", Week = "a"}, 
       new Entity { Status = "2", Week = "c"}, 
       new Entity { Status = "3", Week = "b"}, 
       new Entity { Status = "1", Week = "a"}, 
       new Entity { Status = "1", Week = "a"} 
     }) .AsQueryable();; 



     var result = new List<EntityResult>(); 

     var statuses = data.Select(a => a.Status).Distinct().ToList(); 
     var weeks = data.Select(a => a.Week).Distinct().ToList(); 

     statuses.ForEach(s => { 
      weeks.ForEach(w => { 
       int count = data.Where(a => a.Status == s && a.Week == w).Count(); 

       result.Add(new EntityResult { Status = s, Week = s, Count= count}); 
      }); 
     }); 


     Console.WriteLine(result[0].Count); 
    } 



} 

public class Entity 
{ 
    public string Status; 

    public string Week; 
} 

public class EntityResult 
{ 

    public string Status; 

    public string Week; 

    public int Count; 
}