假设您有一个MyPayments类

 public class Mypayment
{
    public int year { get; set; }
    public string month { get; set; }
    public string price { get; set; }
    public bool ispaid { get; set; }
}

你有一个我的支付列表

public List<Mypayment> mypayments { get; set; }

你要把名单按年分组。你可以这样使用linq:

List<List<Mypayment>> mypayments = (from IGrouping<int, Mypayment> item in yearGroup
                                                let mypayments1 = (from _payment in UserProjects.mypayments
                                                                   where _payment.year == item.Key
                                                                   select _payment).ToList()
                                                select mypayments1).ToList();

foreach (var v in structure) 
{     
    var group = groups.Single(g => g.Key == v. ??? );
    v.ListOfSmth = group.ToList();
}

首先，您需要选择所需的组。然后可以使用组上的ToList方法。IGrouping是值的IEnumerable。

简单地这样做:

// this will "split" the list into groups
var groups = list.GroupBy(x => x.ID);

// groups is a "collection of lists"
foreach (var sublist in groups)
{
  // now the sublist is only a part of the original list
  // to get which is the value of ID, you can use sublist.Key
}

你不需要Select(). groupby (expr)生成“列表的列表”。

因为IGrouping<TKey, TElement>实现了IEnumerable<TElement>，你可以使用SelectMany把所有的IEnumerable一起放回一个IEnumerable:

List<smth> list = new List<smth>();
IEnumerable<IGrouping<int, smth>> groups = list.GroupBy(x => x.id);
IEnumerable<smth> smths = groups.SelectMany(group => group);
List<smth> newList = smths.ToList();

下面是一个构建/运行的示例:https://dotnetfiddle.net/DyuaaP

解决方案视频解说:https://youtu.be/6BsU1n1KTdo

根据IGrouping的定义:

IGrouping<out TKey, out TElement> : IEnumerable<TElement>, IEnumerable

你可以像这样迭代元素:

IEnumerable<IGrouping<int, smth>> groups = list.GroupBy(x => x.ID)
foreach(IEnumerable<smth> element in groups)
{
//do something
}

以上答案的更明确版本:

IEnumerable<IGrouping<int, ClassA>> groups = list.GroupBy(x => x.PropertyIntOfClassA);

foreach (var groupingByClassA in groups)
{
    int propertyIntOfClassA = groupingByClassA.Key;

    //iterating through values
    foreach (var classA in groupingByClassA)
    {
        int key = classA.PropertyIntOfClassA;
    }
}