How to use explain on a Map Reduce query in MongoDB and PHP
===

I was doing a simple query using explain to know precisely the execution time.

        $this->db->toto->find($req)->sort(array('date' => 1))->explain();

I now want to use explain on a map and reduce query, how to do that ?
Should I use the 'classic' profiling system?

ex:

        $res = $this->db->command(array(
            "mapreduce" => "toto",
            "map" => $map,
            "reduce" => $reduce,
            "finalize" => $finalize,
            "query" => $req,
            "out" => array("inline"=>1)
        ))->explain();

Doesn't work because command return an array (explain need a MongoCursor).

Thanks you a lot :)