在linq分组

Question

我有dataTables我想找到课程类似

的null专业化

Specization     course    year

null              IT        0
null              IT        0
null             Math       0

如果在LINQ中进行查询

var NospecList = (from r in dt.AsEnumerable()
                  where r.Field<decimal>("year") == 0 && r.Field<string>("Specization  ") == null
                  group r by r.Field<string>("course"));

但在linq中找不到以下结果

IT -> 2

Math -> 1

我想要计算其专业化为null的所有课程

Answer 1

var NospecList = (from r in dt.AsEnumerable()
                  where r.Field<decimal>("year") == 0 && r.Field<string>("Specization  ") == null
                  group r by r.Field<string>("course") into g
                  select new {Course=g.Key, Count=g.Count()});

<强>结果：

IT -> 2

Math -> 1

更新：

如果您想在foreach中使用它，只需：

foreach(var item in NospecList )
{
   //item.Course
   //item.Count
}

Answer 2

您的查询缺少“选择”语句。试试这个。

var NospecList = (from r in dt.AsEnumerable()
              where r.Field<decimal>("year") == 0 && r.Field<string>("Specization  ") == null
              group r by r.Field<string>("course") into grp
              select new {Course = grp.Key, Count = grp.Count()});