Counting grouped data with Linq to Sql

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开发者_StackOverflow社区 ids of the most common document types. I'm not too familiar with Linq to Sql, so any help would be great.

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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.

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Using the Select you can get the value from the Key of the Grouping (the Id) and then a count of each item in the grouping.

var docTypes = _documentRepository.GetAll()                   
.Where(x => x.Owner.Id == LoggedInUser.Id)                   
.GroupBy(x => x.DocumentType.Id)
.Select(groupingById=> 
  new
  {
    Id = groupingById.Key,
    Count = groupingById.Count(),
  })
.OrderByDescending(x => x.Count);