mapreduce - Map-Reduce count number of documents in each minute MongoDB -

i have mongodb collection has created_at stored in each document. these stored mongodb date object e.g.

{ "_id" : "4cacda7eed607e095201df00", "created_at" : "wed oct 06 2010 21:22:23 gmt+0100 (bst)", text: "something" } { "_id" : "4cacdf31ed607e0952031b70", "created_at" : "wed oct 06 2010 21:23:42 gmt+0100     (bst)", text: "something" } .... 

i count number of items created between each minute, can pass data google charts generate this:

how do map reduce function, or there fancy mongodb aggregate function use instead?

map function should emit timestamp object, adjusted minute, , count of 1. reduce function should sum counts:

map = function() {     var created_at_minute = new date(this.created_at.getfullyear(),                                      this.created_at.getmonth(),                                       this.created_at.getdate(),                                       this.created_at.gethours(),                                       this.created_at.getminutes());     emit(created_at_minute, {count: 1}); }  reduce = function(key, values) {      var total = 0;     for(var = 0; < values.length; i++) {          total += values[i].count;      }     return {count: total}; }