集团通过LINQ [英] Group by in LINQ

问题描述

让如果我们有像

class Person { 
    internal int PersonID; 
    internal string car  ; 
}

现在我有这个类的列表：列表＆LT;＆人GT;人;

Now I have a list of this class: List<Person> persons;

现在这个名单可以有多个实例相同PersonIDs，为前。

Now this list can have instances multiple same PersonIDs, for ex.

persons[0] = new Person { PersonID = 1, car = "Ferrari" }; 
persons[1] = new Person { PersonID = 1, car = "BMW"     }; 
persons[2] = new Person { PersonID = 2, car = "Audi"    }; 

有没有一种方法，我可以按PERSONID，并得到他的全部汽车的名单？
外汇。预计结果将是

Is there a way I can group by personID and get the list of all the cars he has? For ex. expected result would be

class Result { 
   int PersonID;
   List<string> cars; 
}

所以分组后我会得到：

So after grouping by I would get:

results[0].PersonID = 1; 
List<string> cars = results[0].cars; 

result[1].PersonID = 2; 
List<string> cars = result[1].cars;

这是我迄今所做的：

var results = from p in persons
              group p by p.PersonID into g
              select new { PersonID = g.Key, // this is where I am not sure what to do

可能有人请点我朝着正确的方向？

Could someone please point me in the right direction?

推荐答案

当然 - 你基本上要：

Absolutely - you basically want:

var results = from p in persons
              group p.car by p.PersonId into g
              select new { PersonId = g.Key, Cars = g.ToList() };

，或作为非查询前pression：

Or as a non-query expression:

var results = persons.GroupBy( p => p.PersonId, 
                               p => p.car,
                               (key, g) => new { 
                                                 PersonId = key, 
                                                 Cars = g.ToList() 
                                               }
                              );

组基本内容（当视图为的IEnumerable＆LT; T＆GT; ）是什么值的序列是在投影（点。汽车在这种情况下）present给定键。

Basically the contents of the group (when view as an IEnumerable<T>) is a sequence of whatever values were in the projection (p.car in this case) present for the given key.

更多关于如何 GROUPBY 的作品，看到我的<一个href=\"http://$c$cblog.jonskeet.uk/2011/01/01/reimplementing-linq-to-objects-part-21-groupby/\">Edulinq张贴在话题。

For more on how GroupBy works, see my Edulinq post on the topic.

（我已经改名为是PersonID 到 PERSONID 在上面，要遵循的.NET命名约定的。）

(I've renamed PersonID to PersonId in the above, to follow .NET naming conventions.)

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