mongodb\Collection group()

Fields to group by. If an array or non-code object is passed, it will be the key used to group results. If instance of \MongoDB\BSON\Javascript passed, it will be treated as a function that returns the key to group by.

Initial value of the aggregation counter object.

Function that takes two arguments (the current document and the aggregation to this point) and does the aggregation. Argument will be automatically cast to \MongoDB\BSON\Javascript.

Optional parameters to the group command. Valid options include:

• condition - criteria for including a document in the aggregation.
• finalize - function called once per unique key that takes the final output of the reduce function.

The result of the aggregation.

on failure.