MongoDB Map Reduce Example

mapreduce.js

var source = "STRESS";
var target = "stress_locations";

var map = function () {
    if (this.tweet.user.location.trim()) {
        emit(this.tweet.user.location, 1);
    }
};

var reduce = function(key, values) {
    return values.length;
};

db.tweets.mapReduce(map, reduce, {
    out: {replace:target}, 
    query: {$and:[{"SOURCE":source},{"tweet.user.location":{$exists:true}}]}
});

// db[target].find().forEach( printjson );