C＃LINQ的總和

Question

我需要通過枚舉值得到一個總和。看到這個例子：

在這種來源：

namespace ConsoleApplication 
{ 
    enum fruits { Orange, Grape, Papaya } 

    class item 
    { 
     public fruits fruit; 
     public string foo; 
    } 

    class Program 
    { 
     static void Main(string[] args) 
     { 
      item[] list = new item[] 
      { 
       new item() { fruit = fruits.Orange, foo = "afc" }, 
       new item() { fruit = fruits.Orange, foo = "dsf" }, 
       new item() { fruit = fruits.Orange, foo = "gsi" }, 
       new item() { fruit = fruits.Orange, foo = "jskl" }, 
       new item() { fruit = fruits.Grape, foo = "mno" }, 
       new item() { fruit = fruits.Grape, foo = "pqu" }, 
       new item() { fruit = fruits.Grape, foo = "tvs" }, 
      }; 

      var vTotals = from... //Here 


     } 
    } 
} 

我想vTotals是類型

Dictionary<fruits, int> 

的 與價值觀

{ 
    { fruits.Orange, 4 } 
    { fruits.Grape, 3 } 
    { fruits.Papaya, 0 } 
} 

我該怎麼辦呢與Linq？

在此先感謝

Answer 1

你想在這裏做什麼在邏輯上是一個組加入。你想用表示每個水果的序列來表示這個表，然後計算這些組的大小。

var totals = Enum.GetValues(typeof(fruits)).OfType<fruits>() 
    .GroupJoin(list, 
     fruit => fruit, 
     item => item.fruit, 
     (fruit, group) => new { Key = fruit, Value = group.Count() }) 
    .ToDictionary(pair => pair.Key, pair => pair.Value); 

Answer 2

您可以使用組加入所有的水果種類與項目：

var vTotals = from fruits f in Enum.GetValues(typeof(fruits)) 
       join i in list on f equals i.fruit into g 
       select new { 
       Fruit = f, 
       Count = g.Count() 
       }; 

結果：

[ 
    { Fruit: "Orange", Count: 4 }, 
    { Fruit: "Grape", Count: 3 }, 
    { Fruit: "Papaya", Count: 0 } 
] 

Answer 3

下面是做到這一點的方法之一。它可能不會被認爲是漂亮，做這一切在一個查詢，但它（IMO）明確：（代碼感謝D Stanley，誰因爲刪掉了他的答案的第一部分）

var vTotals = list.GroupBy(i => i.fruit) 
       .ToDictionary(g => g.Key, g => g.Count()); 
foreach (var fruit in Enum.GetValues(typeof(fruits)).Cast<fruits>() 
          .Where(x => !vTotals.ContainsKey(x))) 
{ 
    vTotals.Add(fruit, 0); 
} 

Answer 4

var total = from e in Enum.GetValues(typeof(fruits)).OfType<fruits>() 
       select new 
       { 
        Fruit = e, 
        Count = list.Where(f => f.fruit == e).Count() 
       }; 

Answer 5

這應該這樣做

var vTotals = list.GroupBy(item => item.fruit) 
      .Select(item => Tuple.Create(item.Key, item.Count())) 
      .ToDictionary(key => key.Item1, value => value.Item2); 

這裏我們簡單的組的水果名字與他們的計數，後來把它變成一本字典

Answer 6

從@ Servy的回答，如果你想單元測試它，使用MSTest的。

[TestClass] 
public class DummyTests { 
    [TestMethod] 
    public void GroupCountByFruitType() { 
     // arrange 
     var expected = new Dictionary<Fruits, int>() { 
      { Fruits.Grape, 3 } 
      , { Fruits.Orange, 4 } 
      , { Fruits.Papaya, 0 } 
     }; 

     Item[] list = new Item[] { 
      new Item() { Fruit = Fruits.Orange, Foo = "afc" }, 
      new Item() { Fruit = Fruits.Orange, Foo = "dsf" }, 
      new Item() { Fruit = Fruits.Orange, Foo = "gsi" }, 
      new Item() { Fruit = Fruits.Orange, Foo = "jskl" }, 
      new Item() { Fruit = Fruits.Grape, Foo = "mno" }, 
      new Item() { Fruit = Fruits.Grape, Foo = "pqu" }, 
      new Item() { Fruit = Fruits.Grape, Foo = "tvs" } 
     }; 

     // act 
     var actual = Enum.GetValues(typeof(Fruits)).OfType<Fruits>() 
      .GroupJoin(list 
       , fruit => fruit 
       , item => item.Fruit 
       , (fruit, group) => new { Key = fruit, Value = group.Count() }) 
      .ToDictionary(pair => pair.Key, pair => pair.Value);    

     // assert 
     actual.ToList() 
      .ForEach(item => Assert.AreEqual(expected[item.Key], item.Value)); 
    } 

    private class Item { 
     public Fruits Fruit { get; set; } 
     public string Foo { get; set; } 
    } 

    private enum Fruits { 
     Grape, 
     Orange, 
     Papaya 
    } 
}