Need Help How do I perform a query with the library where I need to select the last records recorded and grouped by an element.

[denisVitonis]

How do I perform a query with the library where I need to select the last records recorded and grouped by an element.
the colection name is ExampleCol and the elements _id, Hexample, Hdate

In MYSQL i do this ( SELECT * FROM TABLE WHERE CONDS GROUP BY COLUMN NAME)
In MONGO DB I had a success using this code.

db.ExampleCol.aggregate(
[
{ $sort: { HDate: -1, Hexample: -1 } },
{
$group:
{
_id: "$_Hexample",
"_Hexample": {"$last":"$_Hexample"},
lastHDate: { $last: "$HDate" }
}
}
]
)

How to Mount a query using ur library?
I tried....
$this->mongo_db->aggregate(); -not success;
$this->mongo_db->command(); -not success;