c# - 从具有 List 作为属性的对象列表中获取唯一值

Question

为了说明的目的，我有一个简单的 Employee 类，它有几个字段和一个删除 Certifications 属性中多次出现的方法

public int EmployeeId { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }

        private List<string> certifications = new List<string>();
        public List<string> Certifications
        {
            get { return certifications; }
            set { certifications = value; }
        }

public List<string> RemoveDuplicates(List<string> s)
        {
            List<string> dupesRemoved = s.Distinct().ToList();
            foreach(string str in dupesRemoved)
                Console.WriteLine(str);
            return dupesRemoved;
        }

RemoveDuplicates 方法将删除 Employee 对象的 Certifications 属性中的所有重复字符串。现在考虑我是否有一个 Employee 对象列表。

 Employee e = new Employee();
           List<string> stringList = new List<string>();
           stringList.Add("first");
           stringList.Add("second");
           stringList.Add("third");
           stringList.Add("first");
           e.Certifications = stringList;
          // e.Certifications = e.RemoveDuplicates(e.Certifications); works fine

           Employee e2 = new Employee();
           e2.Certifications.Add("fourth");
           e2.Certifications.Add("fifth");
           e2.Certifications.Add("fifth");
           e2.Certifications.Add("sixth");

           List<Employee> empList = new List<Employee>();
           empList.Add(e);
           empList.Add(e2);

我可以用

foreach (Employee emp in empList)
           {
               emp.Certifications = emp.RemoveDuplicates(emp.Certifications);
           }

从列表中的所有员工那里获取所有唯一认证的列表，但我想在 LINQ 中执行此操作，类似于

stringList = empList.Select(emp => emp.Certifications.Distinct().ToList());

这给了我一个错误提示

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Collections.Generic.List<string>>' to 'System.Collections.Generic.List<string>'. An explicit conversion exists (are you missing a cast?)  

如何从 Employee 对象列表中获取唯一认证列表？

Answer 1

据我了解，您需要所有员工的所有独特认证的列表。这将是 SelectMany 的工作:

var uniqueCerts = empList.SelectMany(e => e.Certifications).Distinct().ToList();