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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.

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Available Operators

OperatorWhat it computes
$avgArithmetic mean
$sumTotal of values
$minSmallest value
$maxLargest value
$countCount of values
$cardinalityCount of distinct values
$statscount, sum, min, max, avg
$extendedStats$stats + variance and std deviation metrics
$percentilesDistribution percent points

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Input Format

Every metric operator takes an object with at least a field property: 
{"alias_name": {"$avg": {"field": "price"}}}
{"alias_name": {"$avg": {"field": "price", "missing": 0}}}
The field value must be a string pointing to a FAST field in your schema. Do not pass a bare string — it must be an object with {"field": "..."}.

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Behavior Notes

  • Metric operators require a field — you will get missing required 'field' property if it’s omitted.
  • The field must be FAST in your schema — otherwise you will get an error: operator '$avg' requires field '<field>' to be FAST. See FAST Fields.
  • 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.