Question

I have a database of documents in an array, each with an owner and a document type, and I’m trying to get a list of the 5 most common document types for a specific user.

var docTypes = _documentRepository.GetAll()
                   .Where(x => x.Owner.Id == LoggedInUser.Id)
                   .GroupBy(x => x.DocumentType.Id);

This returns all the documents belonging to a specific owner and grouped as I need them, I now need a way to extract the ids of the most common document types. I’m not too familiar with Linq to Sql, so any help would be great.

Answer 1

This would order the groups by count descending and then take the top 5 of them, you could adapt to another number or completely take out the Take() if its not needed in your case:

var mostCommon = docTypes.OrderByDescending( x => x.Count()).Take(5);

To just select the top document keys:

var mostCommonDocTypes = docTypes.OrderByDescending( x => x.Count())
                                 .Select( x=> x.Key)
                                 .Take(5);

You can also of course combine this with your original query by appending/chaining it, just separated for clarity in this answer.