Question

In ASP.NET C# I have a struct:

public struct Data
{
    public int item1;
    public int item2;
    public int category_id;
    public string category_name;
}

and I have a List of those. I want to select category_id and category_name, running a DISTINCT and finally an ORDERBY on category_name.

Here’s what I have now:

List<Data> listObject = getData();
string[] catNames = listObject
                    .Select(i=> i.category_name)
                    .Distinct()
                    .OrderByDescending(s => s)
                    .ToArray();

This obviously just gets the category name. My question is, how do I get multiple fields, and what data structure will I store this in (not a string[])?

EDIT

Using a list of structs is not set in stone. If it would be advisable to change my backing data structure to make selects easier (I’ll be writing a lot of these) then I’d gladly take recommendations.

Answer 1

Anonymous types allow you to select arbitrary fields into data structures that are strongly typed later on in your code:

var cats = listObject
    .Select(i => new { i.category_id, i.category_name })
    .Distinct()
    .OrderByDescending(i => i.category_name)
    .ToArray();

Since you (apparently) need to store it for later use, you could use the GroupBy operator:

Data[] cats = listObject
    .GroupBy(i => new { i.category_id, i.category_name })
    .OrderByDescending(g => g.Key.category_name)
    .Select(g => g.First())
    .ToArray();