Question

Hey I have an array where each element is a hash containing a few values and a count.

result = [
           {"count" => 3,"name" => "user1"}, 
           {"count" => 10,"name" => "user2"}, 
           {"count" => 10, "user3"},
           {"count" => 2, "user4"}
         ]

I can sort the array by count as follows:

result = result.sort_by do |r|
  r["count"]
end

Now I want to be able to retrieve the top n entries based on count (not just first(n)) Is there an elegant way to do this?
So as an example, let n = 1 I would expect a result set of.

[{"count" => 10,"name" => "user2"}, {"count" => 10, "user3"}]

since I asked for all entries with the highest score.. if I asked for top 2 highest scores I’d get

 [{"count" => 10,"name" => "user2"}, {"count" => 10, "user3"}, {"count" => 3, "user1"}]

Answer 1

Enumerable#group_by to the rescue (as usual):

result.group_by { |r| r["count"] }
      .sort_by  { |k, v| -k }
      .first(2)
      .map(&:last)
      .flatten

Most of the work is done by the group_by. The sort_by simply lines things up so that first(2) will pick off the groups you want. Then map with last will extract the count/name hashes that you started with and the final flatten will clean up the extra left over arrays.