mongoose mapreduce (public)

gistfile1.js

SomeSchema.methods.mapReduce = function(callback) {

  function map() {
    /*global emit:true */
    emit('something', {foos:this.foos, users:1});
  }

  function reduce(k, av) {
    var foos = 0;
    av.forEach(function(v) {
      foos += v.foos;
    });
    return {foos:foos, users:av.length};
  }

  function finalize(k, v) {
    v.average = Math.floor(v.foos / v.users);
    return v;
  }

  var command = {
        mapreduce : 'collection_name'

      , query: {bar:{$gt: 9}} // we iterate over docs in collection_name with bar>9

      , out: { inline: 1 }
      , map: map.toString()
      , reduce: reduce.toString()
      , finalize: finalize.toString()
  };

  mongoose.connection.db.executeDbCommand(command, function(err, dbres) {
    var out = {foos:0, users:0, average:0}; // this is my default output
    try { out = dbres.documents[0].results[0].value; } catch(e) {}
    callback(err, out);
  });

};