Generating a Structure for Aggregation

Question

So here\'s a question. What I want to do is generate a data structure given a set of input values.

Since this is a multiple language submission, let\'s consider the

Answer 1

First thank you Neil for your help with this here, this workout great for me and it's really fast. For those who use mongoid, this is what I used to create the weight parameter where recommended_user_ids is an array:

    def self.project_recommended_weight recommended_user_ids
      return {} unless recommended_user_ids.present?
      {:weight => create_weight_statement(recommended_user_ids.reverse)}
    end

    def self.create_weight_statement recommended_user_ids, index=0
      return 0 if index == recommended_user_ids.count
      {"$cond" => [{ "$eq" => ["$user_id", recommended_user_ids[index]] },index+1,create_weight_statement(recommended_user_ids,index+1)]}
    end

So to add this to the pipeline simply merge the hash like this:

{"$project" => {:id => 1,:posted_at => 1}.merge(project_recommended_weight(options[:recommended_user_ids]))}