Linq Query for Top 10 with Group BY

Question

Possible Duplicate:
Linq - Top value form each group

I have data in the following structure:

 var lookupDictionary = new Dictionary<string, Dictionary<string, double>>();

I'm trying to write a Linq query to give me the Top 10 keys from the outer dictionary by summing up and ordering descending the doubles in the inner dictionary. I have a good grasp on group by in SQL, but struggle converting that to Linq.

Any Linq experts that can demonstrate this type of query?

http://stackoverflow.com/questions/1575316/linq-top-value-form-each-group — indiPy, Jun 26 '12 at 14:56
It would really make things clearer if you could give an example of your sample input and expected output. — Jon Skeet, Jun 26 '12 at 14:58
Thanks for the link alliswell. I didn't see that one in my initial search. — Paul, Jun 26 '12 at 15:06

score 2 · Accepted Answer · answered Jun 26 '12 at 15:02

2

Do you need a group by?

var top = lookupDictionary
    .Select(dict => new { dict.Key, InnerCount = dict.Value.Values.Sum() })
    .OrderByDescending(dict => dict.InnerCount)
    .Take(10);

answered Jun 26 '12 at 15:02

Dave Bish

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score 1 · Answer 2 · answered Jun 26 '12 at 15:01

Dictionary<string, Dictionary<string, double>> lookupDictionary = new Dictionary<string, Dictionary<string, double>>();
lookupDictionary.Select(outerKeyPair => new
{
    Key = outerKeyPair.Key,
    Sum = outerKeyPair.Value.Values.Sum()
})
.OrderByDescending(pair => pair.Sum)
.Take(10);

Linq Query for Top 10 with Group BY

2 Answers2