C#中對集合排序的三種方式

2022-09-26 14:02:32

對集合排序，可能最先想到的是使用OrderBy方法。

    class Program
    {
        static void Main(string[] args)
        {
            IEnumerable<Student> result = GetStudents().OrderBy(r => r.Score);
            foreach (var item in result)
            {
                Console.WriteLine(item.Name + "--" + item.Score);
            }
            Console.ReadKey();
        }
        private static List<Student> GetStudents()
        {
            return new List<Student>()
            {
                new Student(){Id = 1, Name = "張三",Age = 15, Score = 80},
                new Student(){Id = 2, Name = "李四",Age = 16, Score = 70},
                new Student(){Id = 3, Name = "趙武",Age = 14, Score = 90}
            };
        }
    }
    public class Student 
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public int Score { get; set; }
    }

以上，OrderBy返回的型別是IEnumerable<Student>。

如果想使用List<T>的Sort方法，就需要讓Student實現IComparable<Student>介面。

   class Program
    {
        static void Main(string[] args)
        {
            List<Student> result = GetStudents();
            result.Sort();
            foreach (var item in result)
            {
                Console.WriteLine(item.Name + "--" + item.Score);
            }
            Console.ReadKey();
        }
        private static List<Student> GetStudents()
        {
            return new List<Student>()
            {
                new Student(){Id = 1, Name = "張三",Age = 15, Score = 80},
                new Student(){Id = 2, Name = "李四",Age = 16, Score = 70},
                new Student(){Id = 3, Name = "趙武",Age = 14, Score = 90}
            };
        }
    }
    public class Student : IComparable<Student>
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public int Score { get; set; }
        
        public int CompareTo(Student other)
        {
          return  this.Score.CompareTo(other.Score);
        }
    }

讓Student實現IComparable<Student>介面固然很好，如果Student是一個密封類，我們無法讓其實現IComparable<Student>介面呢？不用擔心，Sort方法提供了一個過載，可以接收IComparer介面型別。

   class Program
    {
        static void Main(string[] args)
        {
            List<Student> result = GetStudents();
            result.Sort(new StudentSorter());
            foreach (var item in result)
            {
                Console.WriteLine(item.Name + "--" + item.Score);
            }
            Console.ReadKey();
        }
        private static List<Student> GetStudents()
        {
            return new List<Student>()
            {
                new Student(){Id = 1, Name = "張三",Age = 15, Score = 80},
                new Student(){Id = 2, Name = "李四",Age = 16, Score = 70},
                new Student(){Id = 3, Name = "趙武",Age = 14, Score = 90}
            };
        }
    }
    public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public int Score { get; set; }
    }
    public class StudentSorter : IComparer<Student>
    {
        public int Compare(Student x, Student y)
        {
            return x.Score.CompareTo(y.Score);
        }
    }

綜上，如果我們想對一個集合排序，大致有三種方式：

1、使用OrderBy方法，返回IEnumerable<T>型別。
2、讓集合元素實現IComparable<T>介面，再使用Sort方法，返回void。
3、集合元素不實現IComparable<T>介面，針對集合元素型別寫一個實現IComparer<T>介面的類，把該類範例作為Sort方法的引數。

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C#中對集合排序的三種方式

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