Counting average on list field

Question

I have list of A, and I want to count average on it's field a.
What's the best way to do it?

class A
{
    int a;
    int b;
}
void f()
{
    var L = new List<A>();
    for (int i=0; i<3; i++)
    {
        L.Add(new A(){a = i});
    }
}

[Enumerable.Average](http://msdn.microsoft.com/en-us/library/bb548874%28v=vs.100%29.ASPX) — huMpty duMpty, Jun 24 '14 at 12:45

dcastro · Answer 1 · 2014-06-24T12:50:45.757

33

Enumerable.Average has an overload that takes a Func<T, int> as an argument.

using System.Linq;

list.Average(item => item.a);

edited Jun 24 '14 at 12:50

answered Jun 24 '14 at 12:43

dcastro

@D Stanley, why Select() is not good in this case? any disadvantage in terms of performance? – Sheen Jun 24 '14 at 13:06
@Sheen Although in most cases it won't be noticeable, there is a slight perf hit because you've added another enumerator on top of average's enumerator. That's an extra level of indirection. But the main problem is: you don't need it. Calling methods that you don't need hinders readability and increases complexity at best. If you had a big chain of linq method calls, adding needless `Selects` in between would make your eyes bleed. – dcastro Jun 24 '14 at 13:19

score 5 · Answer 2 · answered Jun 24 '14 at 12:44

5

You could try this one:

var average = ListOfA.Select(x=>x.a).Average();

where ListOfA is a List of objects of type A.

answered Jun 24 '14 at 12:44

Christos

score 3 · Answer 3 · answered Jun 24 '14 at 12:43

3

var average = L.Select(r => r.a).Average();

answered Jun 24 '14 at 12:43

Sajeetharan

3 Answers3