How to create an anonymous type list with GroupBy?

Question

C++ / C#

There is a class

class Box
{
     // свойства
    public ProductName { get; set; }
    public IEnumerable<Item> GetItems()
    {
        // Возвращает список Items
    } // GetItems()
} // class Box

Now I have a list of these same Boxes, each of which has different content.
It is necessary to make a grouping a la SQL
SELECT ProductName, COUNT(Items) FROM BOXES GROUP BY ProductName
using LINQ:
There are IEnumerable Boxes
I do:
var list = Boxes.GroupBy( b=> ... ???? )
What should be in brackets?

Answer 1

In brackets - the field by which you group
var list = Boxes.GroupBy(b=> b.ProductName)