Overview

Metric aggregations compute summary numbers over all documents that matched your filter.

Use metrics when you want one value (or stats object), not grouped buckets.

Available Operators

Operator	What it computes
$avg	Arithmetic mean
$sum	Total of values
$min	Smallest value
$max	Largest value
$count	Count of values
$cardinality	Count of distinct values
$stats	count, sum, min, max, avg
$extendedStats	$stats + variance and std deviation metrics
$percentiles	Distribution percent points

Behavior Notes

• Metric operators require a field.
• The field must be FAST in your schema.
• Metric operators do not support nested $aggs.
• For many metric operators, missing lets you provide a fallback value for documents where the field does not exist.