OPTIONS

Group Accumulator OperatorsΒΆ

Accumulators, available only for the $group stage, compute values by combining documents that share the same group key. Accumulators take as input a single expression, evaluating the expression once for each input document, and maintain their state for the group of documents.

Name Description
$sum Returns a sum for each group. Ignores non-numeric values.
$avg Returns an average for each group. Ignores non-numeric values.
$first Returns a value from the first document for each group. Order is only defined if the documents are in a defined order.
$last Returns a value from the last document for each group. Order is only defined if the documents are in a defined order.
$max Returns the highest expression value for each group.
$min Returns the lowest expression value for each group.
$push Returns an array of expression values for each group.
$addToSet Returns an array of unique expression values for each group. Order of the array elements is undefined.

Was this page helpful?

Yes No

Thank you for your feedback!

We're sorry! You can Report a Problem to help us improve this page.