map-reduce-count-imdb-votes.js

db.movies.mapReduce(
        // map
        function(){
            emit(1,this.imdb.votes);
        }, 

        // reduce
        function(key,vals){ 
            var count = 0;
            vals.forEach(function(v) {
                count +=v;
            });

            return count;
        }, 
        {  
            // query  
            query: {
                "imdb.rating": {
                    "$lt": 7.5
                }
            }, 
            // output
            out: "vote_count" 
        }
).find();