数据表LINQ Join C＃

Question

I have the following tables (DataTable):

CallData table has fields Strike , MidPrice and PutData table with fields Strike and Midprice I would like to join them on Strike and choose minimum of the following expression:

Abs(CallData.MidPrice - PutData.MidPrice)

Here is how I image it should look in LINQ terms:

var result = (from CallRow in CallData.AsEnumerable()
              join PutRow in PutData.AsEnumerable()
                on CallRow.Field<int>("Strike") equals PutRow.Field<int>("Strike") 
            select new { Abs(CallRow.Field<double>("MidPrice")
                             - PutRow.Field<double>("MidPrice"))
                       }).Min();

However, expression

 Abs(CallRow.Field<double>("MidPrice")  

is underlined by wavy line and the message says:

Invalid anonymous type member declared. Anonymous type member must be declared with a member assignment simple name or member access.

Any ideas how to correct it?

EDIT: Great answer Selman22! I have found the following example in link

static void GetNameAndDescription {ProductInfo[] products}
{
Console.WriteLine("Names and Descriptions:")
var nameDesc = from p in product select new {p.Name, p.Description};
}

Do you know why this code is valid with 'new'

Answer 1

You don't even need an anonymous type here. Just remove the new part

var result = (from CallRow in CallData.AsEnumerable()
          join PutRow in PutData.AsEnumerable()
          on CallRow.Field<int>("Strike") equals PutRow.Field<int>("Strike") 
          select Abs(CallRow.Field<double>("MidPrice") 
                    - PutRow.Field<double>("MidPrice"))).Min();

The error message explains the reason clearly:

Anonymous type member must be declared with a member assignment simple name or member access.

In this case you have a complex expression, so you need to set the value to a property to make it work. like new { value = Abs(...) } , but as I said already you don't need it...