Parse cloud code get average of SUM Rating

main.js

Parse.Cloud.define("getrating", function(request, response) {
  //Query class appointments
  var query = new Parse.Query("appointments");
  //Query column trainer in appointments pass trainerid object
  query.equalTo("trainer", request.params.trainerid);
  query.find({
    success: function(results) {
      var sum = 0;
      for (var i = 0; i < results.length; ++i) {
        //Get the sum of the field rate for the trainer
        sum += results[i].get("rate");
      }
      response.success(sum / results.length);
    },
    error: function() {
      response.error("Calculating ratings failed");
    }
  });

});