使用 linq 從字段列表中刪除重復項

Question

我是 C# 和 Linq 的新手我面臨一個問題來刪除重復記錄我需要刪除那些沒有Dept重復記錄。 下面是一個使用員工列表的快速示例

 private static void Main()
    {
        List<Employee> empList = new List<Employee>();

        empList.Add(new Employee() { ID = 1, Name = "John", Age=23, Dept='computer'});
        empList.Add(new Employee() { ID = 2, Name = "Mary", Age=25, Dept='computer'});
        empList.Add(new Employee() { ID = 3, Name = "Amber",Age=23, Dept=''});
        empList.Add(new Employee() { ID = 4, Name = "Kathy",Age=25, Dept=''});
        empList.Add(new Employee() { ID = 5, Name = "Lena", Age=27, Dept='computer'});
        empList.Add(new Employee() { ID = 6, Name = "John", Age=28, Dept=''});
        empList.Add(new Employee() { ID = 7, Name = "Kathy",Age=27, Dept='Tester'});
 empList.Add(new Employee() { ID = 8, Name = "John", Age=23, Dept='computer'});
        var dup = empList
            .GroupBy(x => new { x.FName })
            .Select(group => new { Name = group.Key, Count = group.Count() })
            .OrderByDescending(x => x.Count);

        foreach (var x in dup)
        {
            Response.Write(x.Count + " " + x.Name);
        }
    }
    class Employee
    {
        public int ID { get; set; }
        public string FName { get; set; }
        public int Age { get; set; }
        public char Dept { get; set; }
    }

最終輸出看起來像這個輸出示例：-

    empList.Add(new Employee() { ID = 1, Name = "John", Age=23, Dept='computer'});
        empList.Add(new Employee() { ID = 2, Name = "Mary", Age=25, Dept='computer'});
        empList.Add(new Employee() { ID = 3, Name = "Amber",Age=23, Dept=''}); 
        empList.Add(new Employee() { ID = 5, Name = "Lena", Age=27, Dept='computer'});
        empList.Add(new Employee() { ID = 7, Name = "Kathy",Age=27, Dept='Tester'});
 empList.Add(new Employee() { ID = 8, Name = "John", Age=23, Dept='computer'});

我需要刪除那些沒有部門的重復記錄。

條件 1 重復記錄將多次出現，但一條記錄沒有應該刪除的部門。 剩余的記錄將顯示在輸出上

Answer 1

由於 ID 是唯一的，您可以使用這種方法（ Dept似乎是一個字符串）：

var empDupNoDepartment = empList
    .GroupBy(x => String.IsNullOrEmpty(x.Dept) ? int.MinValue : x.ID)
    .Select(group => group.First())
    .ToList();

這僅保留第一個Dept為空的員工。

Answer 2

from e in empList
group e by e.Name into g
select g.FirstOrDefault(e => !String.IsNullOrEmpty(e.Dept)) ?? g.First();

只需按姓名分組，然后選擇第一個有部門的員工或第一個員工。

輸出：

[
  { "ID": 1, "Name": "John", "Age": 23, "Dept": "computer" },
  { "ID": 2, "Name": "Mary", "Age": 25, "Dept": "computer" },
  { "ID": 3, "Name": "Amber", "Age": 23,"Dept": "" },
  { "ID": 7, "Name": "Kathy", "Age": 27, "Dept": "Tester" },
  { "ID": 5, "Name": "Lena", "Age": 27, "Dept": "computer" }
]

---

如果要將所有條目保留為非空 Dept，則

Func<Employee, bool> hasDept = e => !String.IsNullOrEmpty(e.Dept);
var result = empList
       .GroupBy(e => e.Name)
       .SelectMany(g => g.Any(hasDept) ? g.Where(hasDept) : g.Take(1));

查詢語法：

from e in empList
group e by e.Name into g
from e in g.Any(hasDept) ? g.Where(hasDept) : g.Take(1)
select e;

輸出：

[
  { "ID": 1, "Name": "John", "Age": 23, "Dept": "computer" },
  { "ID": 8, "Name": "John", "Age": 23, "Dept": "computer" },  <== difference
  { "ID": 2, "Name": "Mary", "Age": 25, "Dept": "computer" },
  { "ID": 3, "Name": "Amber", "Age": 23,"Dept": "" },
  { "ID": 7, "Name": "Kathy", "Age": 27, "Dept": "Tester" },
  { "ID": 5, "Name": "Lena", "Age": 27, "Dept": "computer" }
]

Answer 3

創建這個類：

class Dept
{
    public int Count { get; set; }
    public string Name { get; set; }
    public List<Employee> Employees { get; set; }
}

這是查詢：

var dup = empList
    .GroupBy(x => new { x.Name })

    // Employees with duplicate name
    .Select(group => new { Emps = group.Select(x => x)})

    // From duplicates select only those that have a department 
    .SelectMany(x => {
        var emps = x.Emps.Where(y => !string.IsNullOrWhiteSpace(y.Dept));
        var employeesWithDept = emps.GroupBy(g => g.Name );


        IEnumerable<Dept> a = 
        employeesWithDept.Select(g => new Dept { Employees = g.ToList(), Name = g.Key.ToString(), Count = g.Count()});
        return a;
    })
    .OrderByDescending(x => x.Count);

Answer 4

你這里有一個例子，說明為什么某人的名字對於任何事情來說都是一個糟糕的主鍵。

所有值：

var hasDept = empList.Where(x=>x.Dept != null && x.Dept.Trim() != string.Empty).ToList();

不同的價值觀：

var hasDept =  empList.Where(x=>x.Dept != null && x.Dept.Trim() != string.Empty).Distinct().ToList();

那些會讓你有一個部門的人。 如果您還想獲取那些沒有但沒有重復條目但確實有部門的條目，最簡單的方法可能是：

var noDept = empList.Where(x=>x.Dept == null || x.Dept.Trim() == string.Empty).Distinct().ToList()  //gets all the ones with no dept

var all = noDept;
foreach(var e in all)
{
        if(hasDept.Where(x.Name == e.Name).Count == 0)
           all.Add(e);
}

Answer 5

我不確定，但是如果您只想使用 Linq 刪除空的 Dept 員工，您應該可以這樣做：

empList = empList.Where(Dept => !string.IsNullOrWhiteSpace(Dept)).Distinct().ToList()

此致 ！