Looking for duplicates / Simple script example

dupscript.js

db.users.group({ key: { name:true }, 
                 cond: { "created_at"}, 
                 initial: { count: 0 }, 
                 reduce: function(obj,out) { out.count ++ ; }});

/*
Note1: make sure you put the initial declaration above reduce or else the count variable never gets set
Note2: group() can't handle more than 10000 unique keys, so for large dbs you are better off using straight up map reduce. 
*/

dupscript_mapreduce.js

m = function () { 
    emit(this.name, 1); 
};
r = function (k, vals) { 
   return Array.sum(vals); 
};

/* shell 

> res = db.users.mapReduce(m,r);
{
	"result" : "tmp.mr.mapreduce_1300684269_8",
	"timeMillis" : 22,
	"counts" : {
		"input" : 11,
		"emit" : 11,
		"output" : 5
	},
	"ok" : 1,
}
> db[res.result].count({ "value": { $gte: 2 }});
3
*/

db[res.result].drop();

Thanks very much for your effort. This helped me a lot!