DataTable:使用LINQ With Criteria字段获取最大值(GroupBy)

Question

我有一个像这样结构的DataTable:

用户名| 价钱

"杰克".01

"杰克".02

"玛丽".03

"玛丽".04

如何在DataTable上使用LINQ返回MAX PRICE FOR JACK(例如:.02)？

设置表的代码(可以忽略).

DataTable tbl = new DataTable();
tbl.Columns.Add("username");
tbl.Columns["username"].DataType = typeof(string);

tbl.Columns.Add("price");
tbl.Columns["price"].DataType = typeof(double);

DataRow r = tbl.NewRow();
r["username"] = "jack"; r["price"] = .01;
tbl.Rows.Add(r);

r = tbl.NewRow();
r["username"] = "jack"; r["price"] = .02;
tbl.Rows.Add(r);

r = tbl.NewRow();
r["username"] = "mary"; r["price"] = .03;
tbl.Rows.Add(r);

r = tbl.NewRow();
r["username"] = "mary"; r["price"] = .04;
tbl.Rows.Add(r);

这是我被卡住的地方.想以最高价格为杰克退回一行(例如:".02").

var result =
    from row in tbl.AsEnumerable() 
    where (string) row["username"] == "jack"
    group row by new {usernameKey = row["username"]} into g  
    select new
    {
        //WHAT IS THE LINQ SYNTAX TO USE HERE?    
        jackHighestPrice = g.Max(x => x.price); //This doesn't work, VS doesn't see the "price" field as strongly typed (not sure why).
    };

//This should display Jack's highest price.  
MessageBox.Show(result.First().jackHighestPrice.ToString());

我不确定如何让Visual Studio将"价格"字段识别为强类型.猜猜它与这个问题有关.

当然,两个查询将起作用(一个用于按用户名过滤,另一个用于选择Max,但它不那么优雅.

与此答案相关.几乎尝试了一切/看了一遍但没有运气.

谢谢.

Answer 1

由于没有price会员,您无法以这种方式访问​​"价格" DataRow.像访问它一样访问它username(按列名称):

var result =
    from row in tbl.AsEnumerable() 
    where (string) row["username"] == "jack"
    group row by new {usernameKey = row["username"]} into g  
    select new
    { 
        jackHighestPrice = g.Max(x => x["price"])
    };

当然你可以这样做:

string max = tbl.AsEnumerable()
        .Where(row => row["username"].ToString() == "jack")
        .Max(row => row["price"])
        .ToString();

Answer 2

你试过了吗:

var query = tbl.AsEnumerable().Where(tr => (string) tr["username"] == "jack")
               .Max(tr => (double) tr["price"]);