假设我们有一个类似的类:
class Person { internal int PersonID; internal string car; }
现在,我有一个此类的清单: List<Person> persons;
List<Person> persons;
现在,此列表可以包含多个具有相同PersonID的实例,例如:
PersonID
persons[0] = new Person { PersonID = 1, car = "Ferrari" }; persons[1] = new Person { PersonID = 1, car = "BMW" }; persons[2] = new Person { PersonID = 2, car = "Audi" };
我有办法分组PersonID并获得他拥有的所有汽车的清单吗?
例如,预期结果将是
class Result { int PersonID; List<string> cars; }
因此,分组后,我会得到:
results[0].PersonID = 1; List<string> cars = results[0].cars; result[1].PersonID = 2; List<string> cars = result[1].cars;
从我到目前为止所做的事情来看:
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
有人能指出我正确的方向吗?
绝对-您基本上想要:
var results = from p in persons group p.car by p.PersonId into g select new { PersonId = g.Key, Cars = g.ToList() };
或作为非查询表达式:
var results = persons.GroupBy( p => p.PersonId, p => p.car, (key, g) => new { PersonId = key, Cars = g.ToList() });
基本上,该组的内容(当视为时IEnumerable<T>)是p.car给定键在投影中(在这种情况下)呈现的任何值的序列。
IEnumerable<T>
p.car
有关如何GroupBy工作的更多信息,请参阅我在Edulinq上有关该主题的帖子。
GroupBy
(在上文中,我已重命名PersonID为PersonId,以遵循.NET命名约定。)
PersonId
另外,您可以使用Lookup:
Lookup
var carsByPersonId = persons.ToLookup(p => p.PersonId, p => p.car);
然后,您可以非常轻松地为每个人购买汽车:
// This will be an empty sequence for any personId not in the lookup var carsForPerson = carsByPersonId[personId];