Accumulators - operators

Accumulator operators are used in aggregation pipelines to perform calculations on grouped data.

	Description
$avg	The $avg operator computes the average of numeric values for documents in a group, bucket, or window.
$bottom	The $bottom operator returns the last document from the query's result set sorted by one or more fields
$bottomN	The $bottomN operator returns the last N documents from the result sorted by one or more fields
$count	The $count operator is used to count the number of documents that match a query filtering criteria.
$first	The $first operator returns the first value in a group according to the group's sorting order.
$firstN	The $firstN operator sorts documents on one or more fields specified by the query and returns the first N document matching the filtering criteria
$last	The $last operator returns the last document from the result sorted by one or more fields
$lastN	The $lastN accumulator operator returns the last N values in a group of documents.
$max	The $max operator returns the maximum value from a set of input values.
$maxN	The $maxN opertor retrieves the top N values based on a specified filtering criteria
$median	The $median operator calculates the median value of a numeric field in a group of documents.
$min	The $min operator retrieves the minimum value for a specified field
$minN	The $minN operator retrieves the bottom N values based on a specified filtering criteria
$percentile	The $percentile operator calculates the percentile of numerical values that match a filtering criteria
$stddevpop	The $stddevpop operator calculates the standard deviation of the specified values
$stddevsamp	The $stddevsamp operator calculates the standard deviation of a specified sample of values and not the entire population
$sum	The $sum operator calculates the sum of the values of a field based on a filtering criteria
$top	The $top operator returns the first document from the result set sorted by one or more fields
$topN	The $topN operator returns the first N documents from the result sorted by one or more fields