Question

我有一个我自己班级的实例列表＆＃34; Vertrag＆＃34; （＆＃34;合同＆＃34;）并需要对它们进行分组。

一个简单的GroupBy正是我所需要的：按最后四个字段分组，结果是IEnumerable＆lt; IGrouping＆lt; ...，Vertrag＆gt;＆gt;。我可以使用这种结果类型，很容易迭代。
在标记的位置......没有给出类型定义。所以这似乎是一个匿名类型？

现在我得到了进一步的要求：确保有最大值。每组三个要素。启动新组（仍然是相同的键！），直到分配完所有组。我在StackOverflow中找到了解决方案，LINQ有点复杂但工作正常。只是返回类型有点复杂我更喜欢将这个复杂的结构转换回简单的IGrouping表单，以便它可以与已有的代码一起使用。

我得到它几乎工作，或者至少简化为一个易于使用的版本，简单的GroupBy版本，但不完全相同。有没有办法自己创建匿名类型的IGrouping，以便不需要更改原始分组后的代码？

密钥会不止一次出现，与GroupBy的意思完全相反。所以我不确定手工制作的IGrouping是否会允许它存在。

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

使用您自己想要的行为实现IGrouping。这将使您的代码更简单。

＆＃34;应用程序＆＃34;：

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();
    }
}

自己生成IGrouping

1 个答案: