分组表达

Question

I have the following object(s) and I want to have a result that provides a collection of objects grouped by first category description and then grouped by subcategory description with:

Category(Count)
SubCategory(Count)
SubCategory(Count)

public class Posting
{
    public Category Category { get; set; }
    public SubCategory SubCategory { get; set; }
}

public class Category
{
    public string Description { get; set; }
}

public class SubCategory
{
    public string Description { get; set; }
}

EDIT

So I have this working like so:

foreach (var category in col.GroupBy(x => x.Category.Description).Select(x => new { CategoryName = x.Key, Items = x }).OrderBy(x => x.CategoryName))
            {
                Console.WriteLine(category.CategoryName);
                foreach (var subCategory in category.Items.GroupBy(x => x.SubCategory.Description).Select(x => new { SubCategoryName = x.Key }).OrderBy(x => x.SubCategoryName))
                {
                    Console.WriteLine("\t" + subCategory.SubCategoryName);
                }
            }

But I would like to get this into one object graph, is that possible?

Answer 1

This seems to be pretty close, with the caveat that the Key field of the "inner" sub-category groupings is an anonymous type containing both the Category and SubCategory. But, depending on what your application is doing, that might be a feature since you'll always have the Category available.

var results = col
    .GroupBy(posting => new
        {
            Category = posting.Category.Description,
            SubCategory = posting.SubCategory.Description
        })
    .GroupBy(group => group.Key.Category.Description);