Map/Reduce Documents inserted per minute

MongoDBDocsPerMinute.js

map = function() {
    var datetime = this._id.getTimestamp();

    var created_at_minute = new Date(datetime.getFullYear(),
                                     datetime.getMonth(),
                                     datetime.getDate(),
                                     datetime.getHours(),
                                     datetime.getMinutes());
    emit(created_at_minute, {count: 1});
}

reduce = function(key, values) {
    var total = 0;
    for(var i = 0; i < values.length; i++) { total += values[i].count; }
    return {count: total};
}

db.so.mapReduce( map, reduce, { out: 'inline' } );
db.inline.find();