c# - 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。我坚持使用现有的(相当烦人的)对象模型来工作，但无论如何......

考虑下面的类，我将把它压缩为仅相关的属性，这样你就明白了……

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。
• 该机构父列表包含一个新对象的列表，该对象具有唯一的指定和所有者组合。
• 现在，对于指定和所有者的每个组合，我们都会得到另一个独特事件的子列表。

所以它基本上有 3 个列表。

我不确定这是否可以通过 IEnumerable List 实现，我已经尝试了很多 GroupBy 扩展方法，但到目前为止都无济于事。我最喜欢这样做，但我正在使用 linq-to-sql 来获取初始的 Assets 列表，如下所示，这可能是开展业务的更好地方......

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()
                            })
    })

我以为你的类(class)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;}
}