自己生成IGrouping

Question

我有一个我自己的类"Vertrag“("Contract")的实例列表，需要对它们进行分组。

一个简单的GroupBy就能做我需要的事情:通过最后四个字段进行分组，结果是一个IEnumerable>。我可以使用这个结果类型，它很容易迭代。

在标有..的地方。没有作为类型定义给出任何内容。所以这似乎是一个匿名类型？

现在我得到了一个进一步的要求:确保有一个最大值。每组三个元素。开始新的组(仍然是相同的键！)直到全部分配完毕。我也在StackOverflow中找到了一个解决方案，LINQ有点复杂，但工作得很好。仅仅返回类型就有点复杂了。

我更喜欢将这个复杂的结构转换回简单的IGrouping形式，这样它就可以与已经存在的代码一起工作。

我让它几乎正常工作，或者至少简化为一个版本，它和简单的GroupBy版本一样容易使用，但不完全相同。有没有办法自己创建匿名类型的IGrouping，这样就不需要按照原始分组来更改代码了？

关键字将不止一次出现相同的地方，这与GroupBy的意图完全相反。因此，我不确定手工制作的IGrouping是否会允许这种情况存在。

这是一个有效的LINQPad示例(带有类型定义)：

void Main() 
{
    List<Vertrag> verträge = new List<Vertrag>();
    verträge.Add(new Vertrag("a1","b1","c","d","e"));
    verträge.Add(new Vertrag("a2","b1","c","d","e"));
    verträge.Add(new Vertrag("a3","b1","c","d","e"));
    verträge.Add(new Vertrag("a4","b1","c","d","e"));
    verträge.Add(new Vertrag("a5","b1","c","d","e"));
    verträge.Add(new Vertrag("a6","b1","c","d","e"));
    verträge.Add(new Vertrag("a7","b1","c","d","e"));
    verträge.Add(new Vertrag("a1","b2","c","d","e"));
    verträge.Add(new Vertrag("a2","b2","c","d","e"));
    verträge.Add(new Vertrag("a3","b2","c","d","e"));
    verträge.Add(new Vertrag("a4","b2","c","d","e"));

    // Very easy first group
    var verträgeGruppiert = verträge
        .GroupBy(v => new { v.Beginn, v.Ende, v.Vorlage, v.Ware });
    verträgeGruppiert.Dump();

    // Far more complex grouping
    var maxInGroup = 3;
    var verträgeGruppiertMax = verträge
        .GroupBy(v => new {v.Beginn, v.Ende, v.Vorlage, v.Ware})
        .Select(g => new 
            {
                Key = g.Key, 
                Teile = g.Select((v,i) => new {Value = v, Index = i})
                    .GroupBy(item => item.Index / maxInGroup)
            });
    verträgeGruppiertMax.Dump();

    // Transform back into simpler style
    // SelectMany used instead select, see comment in question
    var vereinfacht = verträgeGruppiertMax
        .SelectMany(vgm => vgm.Teile
            .Select(t => new 
                { 
                    vgm.Key, 
                    a = t.Select(x => x.Value.ID)
                }));
    vereinfacht.Dump();
}

public class Vertrag 
{
    public Vertrag( // Constructor
        string id,
        string beginn,
        string ende,
        string vorlage,
        string ware)
    {
        ID = id;
        Beginn = beginn;
        Ende = ende;
        Vorlage = vorlage;
        Ware = ware;
    }

    // Fields
    public string ID { get; private set; }
    public string Beginn { get; private set; }
    public string Ende { get; private set; }
    public string Vorlage { get; private set; }
    public string Ware { get; private set; }
}

Answer 1

只需使用自己想要的行为实现IGrouping即可。这将使您的代码变得更简单。

“应用程序”：

var elements = new List<Tuple<string, string, string, string>>();
elements.Add(Tuple.Create("a", "one", "A1", "Banana"));
elements.Add(Tuple.Create("a", "two", "B3", "Orange"));
elements.Add(Tuple.Create("a", "three", "C5", "Kiwi"));
elements.Add(Tuple.Create("a", "four", "D7", "Coconut"));
elements.Add(Tuple.Create("a", "five", "E9", "Maracuja"));
elements.Add(Tuple.Create("b", "one", "A1", "Banana"));
elements.Add(Tuple.Create("b", "two", "B3", "Orange"));
elements.Add(Tuple.Create("b", "three", "C5", "Kiwi"));
elements.Add(Tuple.Create("b", "four", "D7", "Coconut"));
elements.Add(Tuple.Create("b", "five", "E9", "Maracuja"));

var groups = elements.GroupBy(element => element.Item1);
var cuttedGroups = groups.Select(group => CuttedGroup.Create(group, 3));

foreach (var group in cuttedGroups)
{
    foreach (var item in group)
    {
        Console.WriteLine(item);
    }

    Console.WriteLine();
}

CuttedGroup的实现：

public static class CuttedGroup
{
    public static IGrouping<TKey, TElement> Create<TKey, TElement>(IGrouping<TKey, TElement> source, int maximumElements)
    {
        return new CuttedGroup<TKey, TElement>(source, maximumElements);
    }
}

public class CuttedGroup<TKey, TElement> : IGrouping<TKey, TElement>
{
    private IGrouping<TKey, TElement> _Source;
    private int _MaximumElements;

    public CuttedGroup(IGrouping<TKey, TElement> source, int maximumElements)
    {
        // Parameter check omitted...

        _Source = source;
        _MaximumElements = maximumElements;
    }
    public TKey Key
    {
        get { return _Source.Key; }
    }

    public IEnumerator<TElement> GetEnumerator()
    {
        return _Source.Take(_MaximumElements).GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}