如何使用 Linq 获得 Max/Min 的 "Date" 分数与（名称，课程）组

Question

数据表有 4 列

Name  Course    Date    Score
Alex  Math      10/15   90
Bob   Chem      10/28   91
Alex  Math      10/29   91
Alex  Math      12/08   89
Bob   Chem      11/23   97
Alex  Chem      10/16   94
Alex  Chem      10/30   92
Bob   Chem      10/01   94

我可以得到每个对应的（名称，课程）组的所有最高分，最低分和平均分，但是如何获得并输出相应的"Max_Date"和"Min_Date"项max/min分数？比如

Name  Course    Max_Date    Max    Min_Date   Min   Average
Alex  Math      10/29       91     12/08      89    90
Alex  Chem      10/16       94     10/30      92    93
Bob   Chem      11/23       97     10/28      91    94

下面是我的代码，我怎样才能获取日期项？

var result = dt.AsEnumerable()
           .GroupBy(r => new
           {
               name = r.Field<string>("Name"),
               course = r.Field<string>("Course")
           })
           .Select(g => new
           {
               name = g.Key.name,
               course = g.Key.course,
               max = g.Max(r => r.Field<int>("score")),
               min = g.Min(r => r.Field<int>("score")),
               ave = g.Average(r => r.Field<int>("score"))
           }).Distinct().ToList();
foreach (var item in result)
Console.WriteLine(s.name + "\t" + s.course + "\t" + s.max + "\t" + s.min + "\t" + (int)s.ave);

Answer 1

像这样：

dt.AsEnumerable()
.GroupBy(r => new
{
   name = r.Field<string>("Name"),
   course = r.Field<string>("Course")
})
.Select(g => new {
    Group = g,
    MaxEntry = g.First(gg => gg.Field<int>("score") == g.Max(r => r.Field<int>("score")))
})
.Select(g => new
{
   name = g.Group.Key.name,
   course = g.Group.Key.course,
   max = g.MaxEntry.Field<int>("score"),
   maxdate = g.MaxEntry.Field<datetime>("date"),
   min = g.Group.Min(r => r.Field<int>("score")),
   ave = g.Group.Average(r => r.Field<int>("score"))
}).Distinct().ToList();

注意：未经测试，但应该给你一个想法

Answer 2

var result = dt.AsEnumerable()
           .GroupBy(r => new
           {
               name = r.Field<string>("Name"),
               course = r.Field<string>("Course")
           })
           .Select(g => new
           {
               name = g.Key.name,
               course = g.Key.course,
               max = g.Max(r => r.Field<int>("score")),
Max_Date    = g.FirstOrDefault(x=> x.Field<int>("score")==g.Max(r => r.Field<int>("score")).Date    ,
Min_Date= g.FirstOrDefault(x=> x.Field<int>("score")==g.Min(r => r.Field<int>("score")).Date    ,
               min = g.Min(r => r.Field<int>("score")),
               ave = g.Average(r => r.Field<int>("score"))
           }).Distinct().ToList();
foreach (var item in result)
Console.WriteLine(s.name + "\t" + s.course + "\t" + s.max + "\t" + s.min + "\t" + (int)s.ave);

如何使用 Linq 获得 Max/Min 的 "Date" 分数与（名称，课程）组

How to get the "Date" of Max/Min Score with (name, course) group using Linq

c#

linq

ado.net