在 C# 中对具有多列的数组进行排序

Question

C#代码

方法

[System.Web.Services.WebMethod]
    public static SubjectList[] GetStudentList(string location, string program, long batch, string term,string code ,string name)
{
    using (Entities obj = new Entities())
    {
        SubjectListStatus subObjStatus = new SubjectListStatus();
        List<string> rollno = obj.Student_Master.Where(i =>i.Student_Location==location && i.Student_Course==program && i.Student_Batch==batch).Select(i => i.Student_RollNo).ToList();
        foreach (var rollObj in rollno)
        {
            var listLoc = obj.Marks_Master.Where(k => k.Location == location && k.Course_ID == program && k.Subject_ID == code && k.Term_ID == term && k.Student_ID.Equals(rollObj)).ToList();
            foreach (var tempobj in listLoc)
            {
                SubjectList subObj = new SubjectList();
                subObj.Subject_Code = tempobj.Student_ID;                   
                subObj.Total_Obtained = tempobj.Marks_Obtained; ;
                subObj.Total_Outoff = tempobj.Marks_Total; ;
                subObjStatus.Add(subObj);
            }
        }
       //sort Here
        return subObjStatus.ToArray();
    }
}

类

public class SubjectList
{
    public string Subject_Code { get; set; }
    public string Subject_Name { get; set; }      
    public long Total_Obtained { get; set; }
    public long Total_Outoff { get; set; }  
}
public class SubjectListStatus : List<SubjectList>
{
    public void Add(SubjectList st)
    {
        base.Add(st);
    }

}

我想在返回数据之前对列Total_Obtained 进行降序排序 我试过Array.Sort 但显示以下错误

1）如何使用Array.Sort

2) 任何其他简单的方法来进行这种排序

我把图像作为数据

提前致谢

Answer 1

OrderBy，就像所有 LINQ 扩展方法一样，不会修改对象，它只返回一个您需要存储的序列（或直接返回它们）。所以在你的代码中，

 return subObjStatus.OrderByDescending(x=>x.Total_Obtained).ToArray();

应该可以。另外，我有几个建议：

[System.Web.Services.WebMethod]
    //change to IEnumerable instead of array
    public static IEnumerable<SubjectList> GetStudentList(string location, string program, long batch, string term,string code ,string name)
{
    using (Entities obj = new Entities())
    {
        //If all subObjStatus did is keeping the SubjectList, you don't really need it
        //SubjectListStatus subObjStatus = new SubjectListStatus();
        //Don't store it into list, just keep it lazy loaded
        var rollno = obj.Student_Master.Where(i =>i.Student_Location==location && i.Student_Course==program && i.Student_Batch==batch).Select(i => i.Student_RollNo);
        foreach (var rollObj in rollno)
        {
            //same thing here, keep it lazy loaded
            var listLoc = obj.Marks_Master.Where(k => k.Location == location && k.Course_ID == program && k.Subject_ID == code && k.Term_ID == term && k.Student_ID.Equals(rollObj));
            foreach (var tempobj in listLoc)
            {
                SubjectList subObj = new SubjectList();
                subObj.Subject_Code = tempobj.Student_ID;                   
                subObj.Total_Obtained = tempobj.Marks_Obtained; ;
                subObj.Total_Outoff = tempobj.Marks_Total;
                subObj.Subject_Name = //you probably want the name too 
                yield return subObj;
            }
        }

    }
}

如果您不熟悉，请阅读有关yield 的更多信息。

GetStudentList 的调用者可以枚举结果，或者如果你真的需要它作为数组调用 ToArray。

Answer 2

在您的排序类型中，subObjStatus 仍然是 SubjectListStatus 类型，如果您坚持这样做，您可以这样做

return Array.Sort(subObjStatus.ToArray());

这样你的SubjectList 就必须实现IComparable 接口。或者你可以使用：

return Array.Sort(subObjStatus.ToArray(),//Custom IComparer);

您可以查看更多参考信息

Array.Sort Documentation

否则你可以使用 LINQ 来做到这一点：

subObjStatus.OrderBy(x => x.[variableToSort]);

然后返回。我认为这是更好的方法。

Answer 3

    [System.Web.Services.WebMethod]
    public static SubjectList[] GetStudentList(string location, string program, long batch, string term,string code ,string name)
{
    using (Entities obj = new Entities())
    {
        SubjectListStatus subObjStatus = new SubjectListStatus();
        List<string> rollno = obj.Student_Master.Where(i =>i.Student_Location==location && i.Student_Course==program && i.Student_Batch==batch).Select(i => i.Student_RollNo).ToList();
        foreach (var rollObj in rollno)
        {
            var listLoc = obj.Marks_Master.Where(k => k.Location == location && k.Course_ID == program && k.Subject_ID == code && k.Term_ID == term && k.Student_ID.Equals(rollObj)).ToList();
            foreach (var tempobj in listLoc)
            {
                SubjectList subObj = new SubjectList();
                subObj.Subject_Code = tempobj.Student_ID;                   
                subObj.Total_Obtained = tempobj.Marks_Obtained; ;
                subObj.Total_Outoff = tempobj.Marks_Total; ;
                subObjStatus.Add(subObj);
            }
        }
        //return subObjStatus.ToArray();
    // use the below statement to sort by total_obtained in the descending order
       return subObjStatus.OrderByDescending(x=>x.Total_Obtained).ToArray();
    }
}