IEnumerable的 <IGrouping> 到IEnumerable <List>

Question

所以我有這個：

IEnumerable<IGrouping<UInt64, MyObject>> groupedObjects = myObjectsResults.GroupBy(x => x.Id);

問題是，如何將此結果轉換為IEnumerable<List<MyObject>> ？

這是我可以接受的：

IEnumerable<List<MyObject>> groupedObjects = (myObjectsResults.GroupBy(x => x.Id).SelectMany(group => group).ToList());

這顯然是不正確的。 有任何想法嗎？

Answer 1

IEnumerable<List<MyObject>> groupedObjects = myObjectsResults.GroupBy(x => x.Id)
                                            .Select(group => group.ToList())
                                            .ToList();

Answer 2

我認為解決方案更簡單。

IGrouping是IEnumerable和IEnumerable <T>。

以下是簽名：

#region Assembly System.Core.dll, v4.0.0.0
// C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.Core.dll
#endregion

using System.Collections;
using System.Collections.Generic;

namespace System.Linq
{
  // Summary:
  //     Represents a collection of objects that have a common key.
  //
  // Type parameters:
  //   TKey:
  //     The type of the key of the System.Linq.IGrouping<TKey,TElement>.This type
  //     parameter is covariant. That is, you can use either the type you specified
  //     or any type that is more derived. For more information about covariance and
  //     contravariance, see Covariance and Contravariance in Generics.
  //
  //   TElement:
  //     The type of the values in the System.Linq.IGrouping<TKey,TElement>.
  public interface IGrouping<out TKey, out TElement> : IEnumerable<TElement>, IEnumerable
  {
    // Summary:
    //     Gets the key of the System.Linq.IGrouping<TKey,TElement>.
    //
    // Returns:
    //     The key of the System.Linq.IGrouping<TKey,TElement>.
    TKey Key { get; }
  }
}

Answer 3

另一個舒適的解決方案是使用字典：

IEnumerable<IGrouping<UInt64, MyObject>> groupedObjects = myObjectsResults.GroupBy(x => x.Id);
Dictionary<UInt64, List<MyObject>> objectGroups = groupedObjects.ToDictionary(group => group.Key, group => group.ToList());