LINQ：获取不在记录中的项目 - C#答案

【问题标题】：LINQ: Get an item that is not in the records - C#LINQ：获取不在记录中的项目 - C#
【发布时间】：2016-08-03 22:51:01
【问题描述】：

这是我的POST 回复的一个扩展问题

class EmployeeSchedule
{
   public int Id { get; set; }
   public string Name { get; set; }
   public DateTime WorkDate { get; set; }
   public bool isOff { get; set; }
}

现在在这种情况下，我想从列表中的4/12/2016 中找到一个WorkDate 未找到的Id 作为我的标准。

List<Staff> workers = new List<Staff>()
{
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/11/2016"), IsOff = false},
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/12/2016"), IsOff = false},
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/13/2016"), IsOff = false},
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/14/2016"), IsOff = false},
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/15/2016"), IsOff = false},
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/16/2016"), IsOff = false},
    new Staff { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/17/2016"), IsOff = false},
    new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/11/2016"), IsOff = false},
    // new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/12/2016"), IsOff = false},
    new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/13/2016"), IsOff = false},
    new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/14/2016"), IsOff = false},
    new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/15/2016"), IsOff = false},
    new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/16/2016"), IsOff = false},
    new Staff { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/17/2016"), IsOff = false},
};

到目前为止，我已经尝试过这段代码：

var notInDate = workers.Where(x => !workers.Any(y => Convert.ToDateTime("4/12/2016") != x.WorkDate));

foreach (var item in notInDate)
{
    Console.WriteLine(item.Id + " " + item.WorkDate.Date);
}

其输出为：ID :1 WorkDate: 4/12/2016 12:00:00 AM

还有这个输出：

var notInDate = workers.Where(x => workers.Any(y => Convert.ToDateTime("4/12/2016") != x.WorkDate));

ID :1 WorkDate: 4/11/2016 12:00:00 AM
ID :1 WorkDate: 4/13/2016 12:00:00 AM
ID :1 WorkDate: 4/14/2016 12:00:00 AM
ID :1 WorkDate: 4/15/2016 12:00:00 AM
ID :1 WorkDate: 4/16/2016 12:00:00 AM
ID :1 WorkDate: 4/17/2016 12:00:00 AM
ID :2 WorkDate: 4/11/2016 12:00:00 AM
ID :2 WorkDate: 4/13/2016 12:00:00 AM
ID :2 WorkDate: 4/14/2016 12:00:00 AM
ID :2 WorkDate: 4/15/2016 12:00:00 AM
ID :2 WorkDate: 4/16/2016 12:00:00 AM
ID :2 WorkDate: 4/17/2016 12:00:00 AM

第二个例子刚刚删除了WorkDate is 4/12/2016的记录

我想得到谁的Id = 2，因为那个Id没有4/12/2016的WorkDate

【问题讨论】：

要求不够明确，
我会尽力澄清我的问题，先生
从我在发布的数据中看到的 ID 为 1，其 WorkDate 也为 2016 年 4 月 12 日，您不想要那个，只需要 ID 为 2 的那个吗？
@DavidY 是，因为Id = 2 没有给定 WorkDate 条件的记录。

标签： c# linq ienumerable enumerable

【解决方案1】：

如果您想要当天没有工作的人的所有条目，您需要按 id 分组（以获取每个人的组）并过滤不包含日期的各个组。类似的东西；

var notInDate = 
         // Create a group per employee
  workers.GroupBy (x => x.Id)
         // Keep only groups that didn't work
         .Where (x => !x.Any (y => y.WorkDate == Convert.ToDateTime ("4/12/2016")))
         // Get only the key for each group
         .Select (x => x.Key);

【讨论】：

它仍然是Id = 2 的列表，但我通过编辑您对此var notInDate = // Create a group per employee workers.GroupBy(x => x.Id) // Keep only groups that didn't work .Where(x => !x.Any(y => y.WorkDate == Convert.ToDateTime("4/14/2016"))) // Flatten the groups back to rows .Select(x => x.Key); 的答案获得了结果
我想接受这个答案，请用我建议的代码更新它

【解决方案2】：

您可以这样做，使用GroupBy 对Id 进行分组，然后使用Any 扩展验证员工是否在该日期工作..

var notInDate = workers.GroupBy(g=>g.Id)
                       .Where(x => !x.Any(y => DateTime.ParseExact("4/12/2016","M/d/yyyy", null) == y.WorkDate))
                       .FirstOrDefault();  // Get the first matching staff.
if(notInDate != null)
{
    id = notInDate.Key; // StaffId
}

【讨论】：

太好了，很高兴它对您有所帮助。
先生，它产生了不同的结果，但我批准了 Joachim 的回答
它有效，但我更喜欢上面的答案先生，非常感谢！
别担心，我很高兴它帮助了你。