gistfile1.txt

function agg_session_count(){
  db.logs.mapReduce(
    function(){
      var local_zone = new Date().getTimezoneOffset()
      var br_zone = 3*60;
      var date_br = parseInt(this.when)+(br_zone-local_zone)*60;
      var date = new Date(date_br*1000);
      var date_format = date.getFullYear()+"-"+date.getMonth()+"-"+date.getDate();

      emit(date_format,{event_ids: [this.event_id], count: 1});
    },
    function(key,values){
      var res = {event_ids: [], count: 0}

      var uniques = {};

      values.forEach(function(value) {
        value.event_ids.forEach(function(event_id) {
          uniques[event_id] = 1
        });
      })

      res.event_ids = Object.keys(uniques);
      res.count = res.event_ids.length;

      return res;
    },
    {
      query: {event: 'created', type: 'stop', event_ids: {$ne: "unspecified"}},
      out: 'agg_session_count'
    },
    function(err,res){
      if(err){
        console.log(err);
      } else {
        db.agg_session_count.count(function(err,val){
            changes = val;
            console.log("OK: "+val+" objects");
        });
      }
    }
  );
}