透视 IEnumerable 列表

Question

我正在尝试将一些 groupby/crosstabbing 逻辑应用于用户定义对象的 IEnumerable 列表，并且想知道是否有人可以帮助我。我被一个现有的（相当烦人的）对象模型困住了，但不管怎样……

请考虑以下类，我将仅将其浓缩为相关属性，以便您了解 jist...

public class Holding
{
   private void Institution;
   private string Designation;
   private Owner Owner;
   private Event Event;
   private Shares Shares;
}

我想将其转换为满足以下条件的列表...

• 对象按机构分组。
• 该机构的父列表包含一个新对象列表，该对象具有唯一的名称和所有者组合。
• 现在，对于每一个指定和所有者的组合，我们都会获得另一个独特事件的子列表。

所以它基本上是 3 个深度列表。

我不确定这是否可以通过 IEnumerable 列表实现，到目前为止，我已经玩弄了很多 GroupBy 扩展方法，但无济于事。我最想这样做，但我正在使用 linq-to-sql 来获取如下的初始持股清单，这可能是开展业务的更好场所......

public static List<Holding> GetHoldingsByEvents(
    int eventId1,
    int eventId2)
{
    DataClassesDataContext db = new DataClassesDataContext();

    var q = from h in db.Holdings
             where
               h.EventId == eventId1 ||
               h.EventId == eventId2
             select h;

    return q.Distinct().ToList();
}

任何帮助/指导将不胜感激...

提前致谢。

Answer 1

我正在使用 ToLookup 方法，这是一种分组，它有两个参数，第一个是用于定义组键的函数，下一个是用作选择器的函数（从匹配中获取什么)。

items.ToLookup(c=>c.Institution.InstitutionId, c => new {c.Designation, c.Owner, c.Event})
    .Select(c => new {
        // find the institution using the original Holding list
        Institution = items.First(i=>i.Institution.InstitutionId == c.Key).Institution,
        // create a new property which will hold the groupings by Designation and Onwner
        DesignationOwner = 
                // group (Designation, Owner, Event) of each Institution by Designation and Owner; Select Event as the grouping result
                c.ToLookup(_do => new {_do.Designation, _do.Owner.OwnerId}, _do => _do.Event)
                            .Select(e => new {
                                // create a new Property Designation, from e.Key
                                Designation = e.Key.Designation,
                                // find the Owner from the upper group ( you can use items as well, just be carreful this is about object and will get the first match in list)
                                Owner = c.First(o => o.Owner.OwnerId == e.Key.OwnerId).Owner,
                                // select the grouped events // want Distinct? call Distinct
                                Events = e.Select(ev=>ev)//.Distinct()
                            })
    })

我假设你的课程看起来像这样

public class Holding
{
   public Institution Institution {get; set;}
   public string Designation {get; set;}
   public Owner Owner {get; set;}
   public Event Event {get; set;}   
}
public class Owner 
{
  public int OwnerId {get; set;}
}

public class Event 
{
  public int EventId {get; set;}
}

public class Institution 
{
  public int InstitutionId {get; set;}
}