Question

参考这个问题 - Using Linq to group a list of objects into a new grouped list of list of objects。

这是输入：

List<User> userList = new List<User>();
userList.Add( new User { UserID = 1, UserName = "UserOne", GroupID = 1 } );
userList.Add( new User { UserID = 2, UserName = "UserTwo", GroupID = 1 } );
userList.Add( new User { UserID = 3, UserName = "UserThree", GroupID = 2 } );
userList.Add( new User { UserID = 4, UserName = "UserFour", GroupID = 1 } );
userList.Add( new User { UserID = 5, UserName = "UserFive", GroupID = 3 } );
userList.Add( new User { UserID = 6, UserName = "UserSix", GroupID = 3 } );

我希望结果采用以下格式：

            GroupedUserList
  GroupID    UserIdList     UsersList
    1 ,        [1,2,4],     ["User1", "UserTwo", "UserFour"]
    2 ,          [3],       ["UserThree"]
    3 ,         [5,6],      ["UserFive", "UserSix"]

linq查询是什么？

Answer 1

您可以在GroupID上执行该组，然后以这种方式投影生成的组：

var result = userList.GroupBy(user=>user.GroupID)
                     .Select(group=> new 
                              {
                                GroupID = group.Key,
                                UserIDs = String.Join(",", group.Select(x=>x.UserID)),
                                UserNames = String.Join(",", group.Select(x=>x.UserName))
                              });

result将包含每个GroupID，其中UserID和UserName为逗号分隔字符串。

编辑：

如果您需要List而不是逗号分隔值，则只需移除String.Join来电并使用ToList()实现结果：

var result = userList.GroupBy(user=>user.GroupID)
                     .Select(group=> new 
                              {
                                GroupID = group.Key,
                                UserIDs = group.Select(x=>x.UserID).ToList(),
                                UserNames = group.Select(x=>x.UserName).ToList()
                              });

Answer 2

您确定不想将{UserId，UserName}的每个元组放在一起吗？

GroupId     {UserId, UserName}
   1        {1, "User1}, {2, "UserTwo"}, {4, "UserFour"},
   2        {3, "UserThree"}
  ...

如果您确定不需要，那么您需要在GroupBy之后进行选择：

var result = userList.GroupBy(user => user.UserId)
    .Select(group => new
    {
        UserIdList = group.Select(user => user.UserId).ToList(),
        UsersList = group.Select(user => user.UserName).ToList(),
    });

使用GroupBy分组后，为单独的列创建列表

2 个答案: