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C#中ToDictionary,ToLookup

更多 时间:2014-11-3 类别:编程学习 浏览量:2400

C#中ToDictionary,ToLookup

C#中ToDictionary,ToLookup

一、C#中ToDictionary

ToDictionary中并没有给我们做key的重复值判断,那也就侧面说明ToDictionary在kv中只能是 “一对一”的关系,也就是v中永远只会有一条记录

 

定义

 

  • C# 代码   复制
  • 
    public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>(
        this IEnumerable<TSource> source,
        Func<TSource, TKey> keySelector
    )
    
    		
  •  

    实例

  •  
  • C# 代码   复制
  • 
          class Package
          {
             public string Company { get; set; }
             public double Weight { get; set; }
             public long TrackingNumber { get; set; }
          }
    
          public static void ToDictionaryEx1()
          {
             List<Package> packages =
                 new List<Package>
                         { new Package { Company = "Coho Vineyard", Weight = 25.2, TrackingNumber = 89453312L },
                           new Package { Company = "Lucerne Publishing", Weight = 18.7, TrackingNumber = 89112755L },
                           new Package { Company = "Wingtip Toys", Weight = 6.0, TrackingNumber = 299456122L },
                           new Package { Company = "Adventure Works", Weight = 33.8, TrackingNumber = 4665518773L } };
    
             // Create a Dictionary of Package objects, 
             // using TrackingNumber as the key.
             Dictionary<long, Package> dictionary =
                 packages.ToDictionary(p => p.TrackingNumber);
    
             foreach (KeyValuePair<long, Package> kvp in dictionary)
             {
                outputBlock.Text += String.Format(
                    "Key {0}: {1}, {2} pounds",
                    kvp.Key,
                    kvp.Value.Company,
                    kvp.Value.Weight) + "\\n";
             }
          }
    
    		
  •  

    二、C#中ToLookup

    ToLookup() 方法创建一个类似 字典(Dictionary ) 的列表,这是一个one-to-many集合,一个Key可以对应多个Value。

    Lookup,不像Dictionary, 是不可改变的。 这意味着一旦你创建一个lookup, 你不能添加或删除元素。

     

    定义

     

  • C# 代码   复制
  • 
    public static ILookup<TKey, TSource> ToLookup<TSource, TKey>(
        this IEnumerable<TSource> source,
        Func<TSource, TKey> keySelector
    )
    
    		
  •  

    实例1

  •  
  • C# 代码   复制
  • 
                var dic = ticketlist.ToLookup(i => i.OrderID);
    
                foreach (var item in dic)
                {
                    Console.WriteLine("订单号:" + item.Key);
    
                    foreach (var item1 in item)
                    {
                        Console.WriteLine("\\t\\t" + item1.TicketNo + "  " + item1.Description);
                    }
                }
    
    		
  •  

    实例2、得到某个类别的所有产品

  •  
  • C# 代码   复制
  • 
            private static void PrintCategory(ILookup<string, Product> productsByCategory,string categoryName)
            {
                foreach (var item in productsByCategory[categoryName])
                {
                    Console.WriteLine(item);
                }
            }
    
    		
  •  

    标签:集合
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