The $match

stage is used to specify the grouping criteria within the $group stage.

The $match

stage is used to join multiple collections together before grouping them with

the $group stage.

The $match

stage is used to sort the documents before they are grouped by the $group

stage.

The $match

stage is used to filter documents before they are passed to the $group stage

for grouping.

The $match

stage is used to perform mathematical calculations on the grouped data from the

$group stage.

$set

changes the values of fields. $project can show and hide fields, but it can't

set values of fields.

$project,

$set, and $addFields are all interchangable.

$set is used to create or change values of new

or existing fields. $project can be used to create or change the value of

fields, but it can also be used to specify which fields to show in the

documents in the aggregation pipeline.