C# lambda 有条件地获取不同的值列表
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C# lambda get distinct list of value conditionally
提问by nunu
I have a list of users as given below:
我有一个用户列表，如下所示：
List<User> users = new List<User>();
users.Add(new User(){ UserId = "11", City = "London" });
users.Add(new User(){ UserId = "12", City = "London" });
users.Add(new User(){ UserId = "12", City = "London" });
users.Add(new User(){ UserId = "11", City = "Newyork" });
users.Add(new User(){ UserId = "14", City = "Virginia" });
Here, I want to get distinct UserIDs those have different Cityby C# lambda expression
在这里，我想通过以下方式获得具有不同城市的不同用户 IDC# lambda expression
So, in above case I should get a List<string>which will only contains UserId = 11 item because UserId is same but city is different for both the item.
所以，在上面的例子中，我应该得到一个List<string>只包含 UserId = 11 的项目，因为 UserId 是相同的，但两个项目的城市不同。
Could you please let me know how would I do this by C# lambda code.
你能否让我知道我将如何通过 C# lambda 代码做到这一点。
Thanks in advance.
提前致谢。
采纳答案by Richard
Something like:
就像是：
var result = users.GroupBy(u => u.UserId)
.Where(g => g.Select(u => u.City).Distinct().Count() > 1)
.Select(g => g.Key)
.ToList();
should do it.
应该这样做。
It takes the {UserId,City} pairs and converts into groups of those pairs indexed by UserId; and then looks for cases where there is more than one city in the group. Finally taking the key from the groups for the result.
它采用 {UserId,City} 对并转换为由 UserId 索引的那些对的组；然后查找组中存在多个城市的情况。最后从组中取出密钥以获得结果。
回答by Jon Hanna
from u in users group u.City by u.UserId into grp //group on the id
where grp.Distinct().Count() > 1 // we only want those with more than one distinct city
select grp.Key //we want the key
回答by Sanjay Gupta
var list = users.GroupBy(Obj=>new {Obj.UserID,Obj.City}).Distinct();
