C＃-从列表字典创建新列表

Question

我需要一些有关从列表字典创建新列表的帮助。处理必须以降序进行。我需要创建链接可能发生的各种配对的列表。

var mappings = new Dictionary<string, List<string>>
{
    { "Policy", new List<string> { "PlPolicy" } },
    { "Location", new List<string> { "L1", "L2" } },
    { "Claim", new List<string> { "C1", "C2", "C3" } }
};

foreach (var keyValuePair in mappings.OrderByDescending(x => x.Value.Count))
{
     Console.WriteLine(@"Entity {0} has {1} items.", keyValuePair.Key, keyValuePair.Value.Count);
}

//I need to create lists that pair every kind of pairing that could happen.
//Example: (I think this is every iteration from the above dictionary)
//There are probably more here but this is just a sample.
var listOne = new List<string> {"C1", "L2", "PlPolicy"};
var listTwo = new List<string> {"C1", "L1", "PlPolicy"};
var listThree = new List<string> {"C2", "L2", "PlPolicy"};
var listFour = new List<string> {"C2", "L1", "PlPolicy"};
var listFive = new List<string> {"C3", "L1", "PlPolicy"};
var listSix = new List<string> {"C3", "L2", "PlPolicy"};

此刻我的脑袋被卡住了，不胜感激...谢谢

Answer 1

根据您的示例，您要查找的内容称为字典值的“ cartesian product”。埃里克·利珀特（Eric Lippert）撰写了一系列博客文章，内容涉及C＃中包括one about the generation of cartesian products via a linq extension method的排列和组合集和序列的各种方式。

在引用的链接中，以下

public static class Program
{
    static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
    {
        IEnumerable<IEnumerable<T>> emptyProduct =
          new[] { Enumerable.Empty<T>() };
        return sequences.Aggregate(
          emptyProduct,
          (accumulator, sequence) =>
            from accseq in accumulator
            from item in sequence
            select accseq.Concat(new[] { item }));
    }

    static void Main(string[] args)
    {
        var mappings = new Dictionary<string, List<string>> {
            { "Policy", new List<string> { "PlPolicy" } },
            { "Location", new List<string> { "L1", "L2" } },
            { "Claim", new List<string> { "C1", "C2", "C3" } }
        };
        foreach(var triple in CartesianProduct(mappings.Values)) {
            Console.WriteLine( string.Join(" , ", triple) );
        }
     }
}    

生成

PlPolicy , L1 , C1
PlPolicy , L1 , C2
PlPolicy , L1 , C3
PlPolicy , L2 , C1
PlPolicy , L2 , C2
PlPolicy , L2 , C3

Answer 2

您可以简单地通过使用LINQ对对象进行操作。这是一个例子：

var mappings = new Dictionary<string, List<string>>
      {
          { "Policy", new List<string> { "PlPolicy" } },
          { "Location", new List<string> { "L1", "L2" } },
          { "Claim", new List<string> { "C1", "C2", "C3" } }
      };

      var query = from policy in mappings["Policy"]
                  from location in mappings["Location"]
                  from claim in mappings["Claim"]
                  select new { Policy = policy, Location = location, Claim = claim };

      var list = query.ToList();

      foreach (var item in list)
      {
        Console.WriteLine($"{item.Policy} - {item.Location} - {item.Claim}");
      }