MongoDB unique classifiers per day

unique_classifiers.js

var userMap = function() {
  day = Date.UTC(this.created_at.getFullYear(), this.created_at.getMonth(), this.created_at.getDate());
  emit({ day: day, user_id: this.user_id }, { count: 1 });
}

var userReduce = function(key, values) {
  var count = 0;
  
  values.forEach(function(v) {
    count += v['count'];
  });
  
  return { count: count };
}

db.galaxy_zoo_classifications.mapReduce(userMap, userReduce, { out: 'user_classifications_per_day' })

var classifyMap = function() {
  emit(this['_id']['day'] / 1000, { count: 1 });
}

db.user_classifications_per_day.mapReduce(classifyMap, userReduce, { out: 'classifying_users_per_day' })

db.classifying_users_per_day.findOne()