sample of mongoDB map_reduce

gistfile1.js

var conn = new Mongo();
var db = conn.getDB("oacis_development");

var map = function() {
  // var key = {param1: this.v["L"], param2: this.v["T"] };
  var key = [ this.v["beta"], this.v["h"] ];
  if( this.runs_status_count_cache ) {
    var cache = this.runs_status_count_cache;
    var total_runs = 0;
    for(var stat in cache) {
      if (stat == "cancelled") continue;
      total_runs += cache[stat];
    }
    var val = {finished: cache["finished"], total: total_runs };
    emit(key, val);
  }
  else {
    emit(key, { ids: [this._id]} );
  }
}

var reduce = function(key,values) {
  var reduced = {finished: 0, total: 0, ids: []};
  values.forEach( function(v){
    if( v.finished ) { reduced.finished += v.finished; }
    if( v.total ) { reduced.total += v.total; }
    if( v.ids ) { reduced.ids = reduced.ids.concat(v.ids); }
  });
  return reduced;
}

var result = db.parameter_sets.mapReduce(map, reduce, 
  { query: {simulator_id: ObjectId("522d751f899e533149000002")}, out: {inline:1} }
  );
shellPrint(result);