Getting average value of groups with LINQ

Question

I am trying to split my List into different groups based on a certain value each item in the List has, and then find the average of another value in those groups.

T

Answer 1

You have to use an additional Select, so you're looking for something like this:

var result = students.GroupBy(s => s.Level)
                     .Select(g => new {Level=g.Key, Avg=g.Average(s => s.GPA)});

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Select(g => new {...}) creates an instance of a new anonymous type for each group.

That type has two properties:

• Level, which is the Key property of the group
• Avg, which is the average GPA of the group

Just "imagine" there's this type in use (more or less):

class GroupAverage
{
    public Level Level { get; set; }
    public float Avg { get; set; }
}

var result = students.GroupBy(s => s.Level)
                     .Select(g => new GroupAverage { Level=g.Key, Avg=g.Average(s => s.GPA) } );

but it simply has no name.

---

result is now:

Feel free to round the values if you need to.

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To get the Level with the highest average, simply use

var highest = result.OrderByDescending(a => a.Avg).First().Level;

(Note that this will crash if there are no items in students)

Answer 2

Check this out:

students.GroupBy(s => s.Level, s => s.GPA, 
                (level, scores) => new { Level = level, Avg = scores.Average() }