C
C#•2y ago
Marek

I need help with understanding the flow of LINQ query expressions

Hello, i'm starting to learn the LINQ language and i don't know if i got my understanding of the process of executing right. My "theory" on example below from official Microsoft documentation is this: 1. It splits students into a row of student 2. It groups every student by the Year property into studentGroups 3. It Selects new Anonymous type with Level and HighScore of the group I'm sorry if i messed it up but thats the reason why I'm even creating this post. My theory number two is that everything under from except select and let applies directly to from. I couldn't find which one of these theories is right if even any of them is :D 
var queryGroupMax =
    from student in students
    group student by student.Year into studentGroup
    select new
    {
        Level = studentGroup.Key,
        HighestScore = (
            from student2 in studentGroup
            select student2.ExamScores.Average()
        ).Max()
    };
var queryGroupMax =
    from student in students
    group student by student.Year into studentGroup
    select new
    {
        Level = studentGroup.Key,
        HighestScore = (
            from student2 in studentGroup
            select student2.ExamScores.Average()
        ).Max()
    };
Thanks for your time, Mark PS: I get what it is doing and i do understand all the keywords just don't know the order of execution
2 Replies
Angius
Angius•2y ago
Basically, yeah Would maybe be easier to understand with the better syntax 
var queryGroupMax = students
    .GroupBy(student => student.Year)
    .Select(g => new {
        Level = g.Key,
        HighestScore = g.Select(s => s.ExamScores.Average()).Max()
    });
var queryGroupMax = students
    .GroupBy(student => student.Year)
    .Select(g => new {
        Level = g.Key,
        HighestScore = g.Select(s => s.ExamScores.Average()).Max()
    });
And with the knowledge that every LINQ query can be rewritten as one or more loops
Marek
MarekOP•2y ago
Yeah, thanks, that's way easier to understand. :)

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