Question

如下所示，我需要输出显示添加，更改和删除的学生。我以为我已经研究过如何准确地做到这一点，并继续找到我目前在RemovedStudents()中设置的内容。有没有人有任何可以帮助我完成添加，更改和删除学生方法的示例？我将不胜感激任何帮助！

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace OldandNewStudents
{
    class Program
    {
        static void Main(string[] args)
        {
            //Display lists of students
            Console.WriteLine("Here is the list of old students: ");
            ShowStudents(GetStudentsOld());
            Console.WriteLine("Here is the list of new students: ");
            ShowStudents(GetStudentsNew());

            //Show the additions
            Console.WriteLine("Here is the list Additions: ");

            //Show the changes
            Console.WriteLine("Here is the list of Changes: ");

            //Show the removed students
            Console.WriteLine("Here is the list of removed students: ");
            RemovedStudents(GetStudentsNew(), GetStudentsOld());
            Console.ReadLine();
        }

        public static List<Student> GetStudentsOld()
        {
            List<Student> students = new List<Student>();

            students.Add(new Student("111", "Michael", "Tucker", "Junior", 10));
            students.Add(new Student("222", "Svetlana", "Omelchenko", "Senior", 2));
            students.Add(new Student("333", "Michiko", "Osada", "Senior", 7));
            students.Add(new Student("444", "Hugo", "Garcia", "Junior", 16));
            students.Add(new Student("555", "Cesar", "Garcia", "Freshman", 4));
            students.Add(new Student("666", "Fadi", "Fakhouri", "Senior", 72));
            students.Add(new Student("777", "Hanying", "Feng", "Senior", 11));
            students.Add(new Student("888", "Debra", "Garcia", "Junior", 41));
            students.Add(new Student("999", "Terry", "Adams", "Senior", 6));
            students.Add(new Student("211", "Bob", "Stephenson", "Junior", 150));
            return students;
        }

        public static List<Student> GetStudentsNew()
        {
           List<Student> students = new List<Student>();

            students.Add(new Student("111", "Michael", "Tucker", "Junior", 10));
            students.Add(new Student("222", "Svetlana", "Omelchenko", "Senior", 2));
            students.Add(new Student("333", "Michiko", "Osada", "Senior", 7));
            students.Add(new Student("311", "Sven", "Mortensen", "Freshman", 53));
            students.Add(new Student("444", "Hugo", "Garcia", "Freshman", 16));
            students.Add(new Student("555", "Cesar", "Garcia", "Freshman", 4));
            students.Add(new Student("666", "Fadi", "Fakhouri", "Senior", 72));
            students.Add(new Student("777", "Hanying", "Feng", "Senior", 11));
            students.Add(new Student("888", "Debra", "Garcia", "Junior", 41));
            students.Add(new Student("411", "Lance", "Tucker", "Junior", 60));
            students.Add(new Student("999", "Terry", "Adams", "Senior", 6));
            return students;
        }

        public static void ShowStudents(List<Student> stuList)
        {
            Console.WriteLine();

            foreach (Student s in stuList)
            {
                Console.WriteLine(s);
            }
            Console.WriteLine();
        }

        public static void RemovedStudents(List<Student> stuNewList, List<Student> stuOldList)
        {
            List<Student> removedStudents = stuNewList.Except(stuOldList).ToList();
            IEnumerable<Student> differenceQuery = stuNewList.Except(stuOldList);
            foreach (Student s in differenceQuery)
                Console.WriteLine(s);
        }
    }
}

这是我新更新的RemovedStudents方法：

public static void RemovedStudents(List<Student> stuNewList, List<Student> stuOldList)
    {
        GetStudentsOld().Except(GetStudentsNew());
        foreach (Student s in stuNewList)
            Console.WriteLine("student: {0} {1}", s.FirstName, s.LastName);
    }

这是学生班，但我不允许编辑它：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace OldandNewStudents
{
public class Student
{
    // Sample Student class
    // Each student has a first name, a last name, a class year, and a rank 
    // that indicates academic ranking in the student body.

    public string ID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string StudentYear { get; set; }
    public int StudentRank { get; set; }

    public Student(string idNumber, string firstName, string lastName, string studentYear, int studentRank)
    {
        ID = idNumber;
        FirstName = firstName;
        LastName = lastName;
        StudentYear = studentYear;
        StudentRank = studentRank;
    }


    public override string ToString()
    {
        return ID + " " + FirstName + " " + LastName + " " + StudentYear + " " + StudentRank;
    }
}
}

这是我的新增加方法，但我不确定为什么会收到过载错误：

public static List<Student> GetActualNewStudents(List<Student> oldStudents, List<Student> newStudents)
    {
        List<Student> actualNewStudents = new List<Student>();

        foreach (var student in oldStudents) {
            if (oldStudents[student].ID != newStudents[student].ID)
            {
                actualNewStudents.Add(newStudents[student]);
            }
        }

        return actualNewStudents;
    }

Answer 1

你可以做的是与普通学生一起创建第三个数组，然后对于那些不在那里的学生，考虑新学生数组中的新学生，当然：

编辑：

public static List<Student> GetActualNewStudents(List<Student> oldStudents, List<Stident> newStudents)
    {
        var actualNewStudents = new List<Student>();
        foreach (var item in newStudents)
        {
            if (!oldStudents.Contains(item))
                actualNewStudents.Add(item);

        }
        return actualNewStudents;
    }

Answer 2

使用两个列表的问题是比较，例如Except扩展方法将使用IEquatable的默认实现。您有一个构造函数，但不包括类定义。如果字段和属性仅包含值类型，则应用逐字节比较。如果您有任何引用类型，则需要覆盖默认的Equals方法。如果您只有值类型字段，则以下代码应该有效。

此外：

GetStudentsNew().Except(GetStudentsOld());

删除：

GetStudentsOld.Except(GetStudentsNew());

差：

public diff(IEnumerable<Student> new, IEnumberable<Student> old)
{
    var both = new.AddRange(old); 
    var add = both.Except(new);
    return add.Except(old);
}

我应该注意，Console.WriteLine将无法正常工作，因为您传入的是引用类型，而不是将转换为您期望的字符串的类型。

Answer 3

这很有效，让我得到了我需要的结果：

添加代码：

public static List<Student> GetActualNewStudents(List<Student> oldStudents, List<Student> newStudents)
    {
        //Show the new students
        List<Student> actualNewStudents = newStudents.Where(y => !oldStudents.Any(z => z.ID == y.ID)).ToList();

        return actualNewStudents;
    }

被移除学生代码：

public static List<Student> GetActualRemovedStudents(List<Student> oldStudents, List<Student> newStudents)
    {
        //Show the removed students
        List<Student> actualRemovedStudents = oldStudents.Where(y => !newStudents.Any(z => z.ID == y.ID)).ToList();

        return actualRemovedStudents;
    }

变更代码：

public static List<Student> GetActualChangedStudents(List<Student> oldStudents, List<Student> newStudents)
    {
        //Show the changes
        List<Student> actualChangedStudents = newStudents.Where(y => !oldStudents.Any(z => z.FirstName == y.FirstName && z.LastName == y.LastName && z.StudentRank == y.StudentRank && z.StudentYear == y.StudentYear)).ToList();

        return actualChangedStudents;
    }

如何在两个列表中找出差异？

3 个答案: