| $sum | Sum up values | db.docx.aggregate([{$group : {_id : "$operator", num_docx : {$sum : "$value"}}}]) |
| $avg | Calculates average values | db.docx.aggregate([{$group : {_id : "$operator", num_docx : {$avg : "$value"}}}]) |
| $min / $max | Find min/max values | db.docx.aggregate([{$group : {_id : "$operator", num_docx : {$min : "$value"}}}]) |
| $push | Push values to a result array | db.docx.aggregate([{$group : {_id : "$operator", classes : {$push: "$value"}}}]) |
| $addToSet | Push values to a result array without duplicates | db.docx.aggregate([{$group : {_id : "$operator", classes : {$addToSet : "$value"}}}]) |
| $first / $last | To get the first / last document | db.docx.aggregate([{$group : {_id : "$operator", last_class : {$last : "$value"}}}]) |
