C# 将两个具有不同对象的列表相交
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intersect two lists with different objects
提问by DarthVader
I have a list of ObjA and ObjB as follows:
我有一个 ObjA 和 ObjB 的列表，如下所示：
List<ObjA> List1;
List<ObjB> List2;
Both ObjA and ObjB has a common field which is User and I want to intersect them based on User.Id.
ObjA 和 ObjB 都有一个公共字段，即 User，我想根据 User.Id 将它们相交。
class ObjA
{
User user;
.... other properties
}
class ObjB
{
User user;
.... other properties
}
class User
{
int Id;
.... other props
}
How can i intersect these two lists on User.Id with linq?
如何将 User.Id 上的这两个列表与 linq 相交？
As a result I want only the list of Users.
结果我只想要用户列表。
采纳答案by Jon
The general idea is
一般的想法是
var commonUsers = list1.Select(a => a.User).Intersect(list2.Select(b => b.User));
However, by itself this assumes that Userimplements IEquatable<User>, which does not seem to be the case here. So you either need to add this implementation or use the Intersectoverload that accepts a custom IEqualityComparer<User>.
但是，这本身就假定了Userimplements IEquatable<User>，而这里似乎并非如此。因此，您要么需要添加此实现，要么使用Intersect接受自定义IEqualityComparer<User>.
回答by rossipedia
The standard way is to utilize an IEqualityComparerobject. The default one uses the standard equality comparison. Create a class that implements the IEqualityComparerinterface and performs the comparison you want. Then you can call an overload of IEnumerable.Intersectthat accepts an instance of your custom compare class
标准的方法是利用一个IEqualityComparer对象。默认使用标准的相等比较。创建一个实现IEqualityComparer接口并执行所需比较的类。然后您可以调用IEnumerable.Intersect接受自定义比较类实例的重载
回答by Rapha?l Althaus
without need of IEqualityComparer or IEquatable (which would be better anyway)
不需要 IEqualityComparer 或 IEquatable （反正会更好）
var commonUsers = list1
.Select(l1 => l1.User)
.Where(u => list1
.Select(l => l.User.Id)
.Intersect(list2
.Select(l2 => l2.Id))
.Contains(u.Id));
or
或者
var commonUsers = list1.Select(l1 => l1.User)
.Where(u=> list2.Select(l2 => l2.User.Id)
.Contains(u.Id));
回答by anuo
1.look at this simple code
1.看这个简单的代码
var result = (from objA in objAList
join objB in objBList on objA.user.Id equals objB.user.Id
select objA/*or objB*/).ToList();
2.complete code
2.完整代码
class QueryJoin
{
static void Main(string[] args)
{
//create users
User user1 = new User { Id = 1, Name = "anuo1" };
User user2 = new User { Id = 2, Name = "anuo2" };
User user3 = new User { Id = 3, Name = "anuo3" };
User user4 = new User { Id = 4, Name = "anuo4" };
User user5 = new User { Id = 5, Name = "anuo5" };
//create objAList
List<ObjA> objAList = new List<ObjA>();
objAList.Add(new ObjA { user = user1 });
objAList.Add(new ObjA { user = user2 });
objAList.Add(new ObjA { user = user3 });
//create objBList
List<ObjB> objBList = new List<ObjB>();
objBList.Add(new ObjB { user = user3 });
objBList.Add(new ObjB { user = user4 });
objBList.Add(new ObjB { user = user5 });
//intersect
var result = (from objA in objAList
join objB in objBList on objA.user.Id equals objB.user.Id
select objA/*or objB*/).ToList();
}
}
class ObjA
{
public User user { get; set; }
}
class ObjB
{
public User user { get; set; }
}
class User
{
public int Id { get; set; }
public string Name { get; set; }
}
