Counting average on list<T> 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});
    }
}

Answer 1

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

using System.Linq;

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