Question

我正在尝试对一组对象进行分组，按名称排序，但我还想在每个组中设置一个顺序的InstanceID属性，以便我有以下内容：

Name="A", InstanceID=0
Name="A", InstanceID=1
Name="A", InstanceID=2
Name="B", InstanceID=0
Name="C", InstanceID=0
Name="C", InstanceID=1
Name="C", InstanceID=2
Name="D", InstanceID=0
Name="D", InstanceID=1
Name="D", InstanceID=2
Name="D", InstanceID=3

等

我假设在GroupBy之后通过LINQ应用了一些投影但我不知道如何在Select或SelectMany中使用累加器或索引

我不想创建新集合，只修改现有集合，在每个元素上设置InstanceID。

Answer 1

您可以GroupBy Name，然后为每个组设置InstanceID属性：

var groups = objects.GroupBy(m => m.Name);

foreach (var group in groups)
{
    int index = 0;
    foreach (var item in group)
        item.InstanceID = index++;
}

修改

您可以创建接收项目和索引的扩展方法ForEach：

static class Extensions { public static void ForEach<T>(this IEnumerable<T> collection, Action<T> action) { foreach (var item in collection) action(item); } public static void ForEach<T>(this IEnumerable<T> collection, Action<T, int> action) { int index = 0; foreach (var item in collection) action(item, index++); } }

并像这样使用它：

var groups = objects.GroupBy(m => m.Name); groups.ForEach(g => g.ForEach((o, i) => o.InstanceID = i));

Answer 2

您可以使用GroupBy，然后使用投射该索引的Select重载：

var groups = objects
    .GroupBy(x => x.Name)
    .Select(g => g.Select((obj, index) => new { Object = obj, Index = index }));

foreach(var grp in groups)
    foreach(var x in grp)
        x.Object.InstanceID = x.Index;

如果您对这些群组并不感兴趣，并且在确定索引后想要展平它们，您还可以使用SelectMany和一个循环：

var items = objects
    .GroupBy(x => x.Name)
    .SelectMany(g => g.Select((obj, index) => new { Object = obj, Index = index }));

foreach(var x in items)
    x.Object.InstanceID = x.Index;

Answer 3

选择的重载会为您提供索引

var list = otherList.Select((model, index) => new { Index=index, ... })

在你的情况下，它可以像这样使用

list = list
        .OrderBy(m => m.Name)
        .GroupBy(m => m.Name)
        .SelectMany(g => g.Select((m, i) => new NameOfClass { InstanceID = i, Name = m.Name } ))
        .ToList();

Answer 4

为了简单起见，我会使用这样的类：

public class StudentSubject
{
    public string Subject { get; set; }
    public string Student { get; set; }
    public int ID { get; set; }

}

列表必须以某种方式填充：

        var list = new List<StudentSubject>();
        list.Add(new StudentSubject
        {
            Subject = "Physics",
            Student = "Steve"
        });
        list.Add(new StudentSubject
        {
            Subject = "Physics",
            Student = "Sarah"
        });
....

然后遍历列表：

        var subjectGroups = from subjectStudent in list
                            group subjectStudent by subjectStudent.Subject;

        foreach(var subjectNameGroup in subjectGroups)
        {
            int id = 0;
            foreach (var studentSubject in subjectNameGroup)
            {
                studentSubject.ID = id;
                id++;
            }
        }

Answer 5

使用查询表达式的解决方案：

class Person
{
    public string Name {get; set;}
    public int Instance {get; set;}
}

Person p1 = new Person {Name ="C"};
Person p2 = new Person {Name ="B"};
Person p3 = new Person {Name ="A"};
Person p4 = new Person {Name ="C"};
Person p5 = new Person {Name ="C"};
Person p6 = new Person {Name ="B"};

var persons = new List<Person>{p1, p2, p3, p4, p5, p6};

var result = from p in persons
             group p by p.Name into g orderby g.Key
             from gr in g.Select((x,i) => new {Value = x, Index = i})
             select gr;

result.ToList().ForEach(x => x.Value.Instance = x.Index);

C＃将序列号应用于组项

5 个答案: