扩展 IEnumerable<T>，让它根据另一个集合的顺序来排列-白红宇

扩展 IEnumerable<T>，让它根据另一个集合的顺序来排列

阅读量：4316 次

发布时间：2019-06-06

本文共 3435 字，大约阅读时间需要 11 分钟。

假如我有两个集合：

public class Teacher{    public int Id { get; set; }    public string Name { get; set; }}public class Student{    public int Id { get; set; }    public string UserName { get; set; }    public int TeacherId { get; set; }}

集合代码：

static void Main(string[] args){    IEnumerable
     
       teachers = new Teacher[]    {        new Teacher{ Id = 9, Name = "CCC" },        new Teacher{ Id = 5, Name = "AAA" },        new Teacher{ Id = 7, Name = "BBB" },        new Teacher{ Id = 13, Name = "DDD" },    };    IEnumerable
      
        students = new Student[]    {        new Student{ Id = 1, TeacherId = 13, UserName = "张三" },        new Student{ Id = 2, TeacherId = 5, UserName = "李四" },        new Student{ Id = 3, TeacherId = 9, UserName = "王五" },        new Student{ Id = 4, TeacherId = 18, UserName = "赵六" },    };}

前提条件：students 里面的 TeacherId 大部分来自于 teachers 里的 ID，也可能不是。

现在要求：按 teachers 的顺序来对 students 里面的项排序。

我的代码如下：

首先扩展 IEnumerable<T>

public static class EnumerableExtensions{    ///     /// 按照另一个现有的集合的关联字段来排序    /// 
    /// 
     
      类型1
         /// 
     
      类型2
         /// 要排序的集合    /// 参考的集合    /// 条件    /// 
         public static IEnumerable
     
       OrderByOther
      
       (this IEnumerable
       
         source1, IEnumerable
        
          source2, Func
         
           condition)    {        if (source1 == null)        {            throw new ArgumentNullException("source1");        }        if (source2 == null)        {            throw new ArgumentNullException("source2");        }        if (condition == null)        {            throw new ArgumentNullException("condition");        }        int source1Count = source1.Count();        SortedDictionary
          
            values = new SortedDictionary
           
            (); // 3, 0, 2, -1, -1 for (int i = 0; i < source1Count; i++) { var item = source1.ElementAt(i); var tempIndex = source2.FirstIndex(s => condition(item, s)); values.Add(tempIndex, item); } foreach (var item in values) { yield return item.Value; } } /// 
             /// 得到满足条件的第一个元素在集合中所在的索引 /// 
 /// 
            
             类型
             /// 
            目标集合 /// 
            条件 /// 
            
             如果没有找到，返回 -1
             public static int FirstIndex
            
             (this IEnumerable
             
               source, Predicate
              
                condition) { if (source == null) { throw new ArgumentNullException("source"); } if (condition == null) { throw new ArgumentNullException("condition"); } int i = 0; foreach (var item in source) { if (condition(item)) { return i; } i++; } return -1; }}

然后测试代码如下：

static void Main(string[] args){    IEnumerable
     
       teachers = new Teacher[]    {        new Teacher{ Id = 9, Name = "CCC" },        new Teacher{ Id = 5, Name = "AAA" },        new Teacher{ Id = 7, Name = "BBB" },        new Teacher{ Id = 13, Name = "DDD" },    };    IEnumerable
      
        students = new Student[]    {        new Student{ Id = 1, TeacherId = 13, UserName = "张三" },        new Student{ Id = 2, TeacherId = 5, UserName = "李四" },        new Student{ Id = 3, TeacherId = 9, UserName = "王五" },        new Student{ Id = 4, TeacherId = 18, UserName = "赵六" },    };    // 前提条件：students 里面的 TeacherId 大部分来自于 teachers 里的 ID， 也可能不是。    // 现在要求：按 teachers 的 顺序 来对 students 里面的项排序。    var result = students.OrderByOther(teachers, (a, b) => a.TeacherId == b.Id);    foreach (var item in result)    {        Console.WriteLine("stuId:" + item.TeacherId + ", stuName:" + item.UserName);    }}

运行结果：