如何使用LINQ创建嵌套的group-by字典？

Question

如何使用LINQ为下表创建嵌套分组？我想分组Code,然后分组Mktcode.

Code Mktcode Id
==== ======= ====
1    10      0001 
2    20      0010 
1    10      0012 
1    20      0010 
1    20      0014 
2    20      0001
2    30      0002
1    30      0002
1    30      0005

我最喜欢的是字典

Dictionary<Code, List<Dictionary<Mktcode, List<Id>>>>

所以这本词典的价值就是

{1, ({10,(0001,0012)}, {20,(0010,0014)}, {30, (0002, 0005)})},
{2, ({20,(0001, 0010)}, {30, (0020)} )}

Answer 1

我会这样想的:

• 您主要是按代码分组,所以首先要这样做
• 对于每个组,您仍然有一个结果列表 - 所以在那里应用另一个分组.

就像是:

var groupedByCode = source.GroupBy(x => x.Code);

var groupedByCodeAndThenId = groupedByCode.Select(group =>
    new { Key=group.Key, NestedGroup = group.ToLookup
                                         (result => result.MktCode, result => result.Id));

var dictionary = groupedByCodeAndThenId.ToDictionary
    (result => result.Key, result => result.NestedGroup);

这会给你一个Dictionary<Code, Lookup<MktCode, Id>>- 我认为这就是你想要的.但它完全未经测试.

Answer 2

您可以使用构建查找(种类的词典<,List <>>) group by into

var lines = new []
{
    new {Code = 1, MktCode = 10, Id = 1},
    new {Code = 2, MktCode = 20, Id = 10},
    new {Code = 1, MktCode = 10, Id = 12},
    new {Code = 1, MktCode = 20, Id = 10},
    new {Code = 1, MktCode = 20, Id = 14},
    new {Code = 2, MktCode = 20, Id = 1},
    new {Code = 2, MktCode = 30, Id = 2},
    new {Code = 1, MktCode = 30, Id = 2},
    new {Code = 1, MktCode = 30, Id = 5},
};

var groups = from line in lines
    group line by line.Code
    into codeGroup
    select new
    {
        Code = codeGroup.Key,
        Items = from l in codeGroup
            group l by l.MktCode into mktCodeGroup
            select new
            {
                MktCode = mktCodeGroup.Key, 
                Ids = from mktLine in mktCodeGroup
                    select mktLine.Id
            }
    };

Answer 3

这是我如何做到的:

Dictionary<Code, Dictionary<MktCode, List<Id>>> myStructure =
  myList
    .GroupBy(e => e.Code)
    .ToDictionary(
      g => g.Key,
      g => g
        .GroupBy(e => e.Mktcode)
        .ToDictionary(
          g2 => g2.Key,
          g2 => g2.Select(e => e.Id).ToList()
        )
   )

这是过程的细分:

按代码对元素进行分组,并创建一个外部字典,其中键是该代码.

  myList
    .GroupBy(e => e.Code)
    .ToDictionary(
      g => g.Key,

对于外部字典中的每个键,通过Mktcode重新组合元素并创建内部字典.

      g => g
        .GroupBy(e => e.Mktcode)
        .ToDictionary(
          g2 => g2.Key,

对于内部字典中的每个键,投影这些元素的id并将其转换为列表.

          g2 => g2.Select(e => e.Id).ToList()
        )
   )