检查列表中的每个项目是否属于某个组并创建一个新列表

Question

I have a list of stored ids. I need to group these id into a separate group of list based on if each id belongs to certain group. For instance in below example, I would like to return:

List<Group1> = {1,2};
List<Group2> = {3,4};
List<Group3> = {5};

Now I have hundreds of group, so i can't literally create a group and add items to that group. So, how can I create and return these groups dynamically?

List<int> list = new List<int> { 1, 2, 3, 4, 5 };   
foreach (int i in list)
{
 var x = PersonList.GetById(I); //Returns Person object
 var obj = x.GroupBy(y => y.GroupName).ToList();
// where obj is IEnumerable<IGrouping<string,Person>>
// I can get Group1 from Person object
//how to get List<Group2> ...and so on?
}

Answer 1

You need to do this

var obj = x.GroupBy(y => y.GroupName); // IEnumerable<IGrouping<string,Person>>

Now in order to get list that belongs to certain group you need to check the IGrouping's key with your own key (that you used to make grouping).

var group2 = obj.Where(g => g.Key == "Group2").SelectMany(g => g).ToList();

Answer 2

如果只希望将人员分组，则下面的查询会将其放入词典中，词典的关键字将是组名，值将是Person对象的列表。

var groups = obj.ToDictionary( t => t.Key, t => t);