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$avg

Definition

Averages numeric values from one array expression or explicit operands; ignores nonnumeric values.

Expression operator · Arithmetic · Studio Visual: available. Studio validates the complete expression separately.

Syntax

{ "$avg": [ <number>, ... ] }

Replace angle-bracket placeholders with expressions or values.

Optional parameters may be omitted.

Parameters

Parameter Required Description
number See argument count below Numeric expression. Repeat the argument when the syntax accepts multiple operands.

Arguments are positional: keep the order shown. Supply 0 or more arguments.

A single array-valued expression is also supported, for example {"$avg": "$items"}. With multiple operands, array arguments are not recursively flattened.

Behavior

The following observations use the example expression below. Each row substitutes one argument while retaining the other example arguments. A missing field differs from an explicit null; the result shown is what Core actually returned.

For the number argument:

Input case Supplied value Result
null null 4.0 (double)
missing Field absent 4.0 (double)
decimal 2.5 3.25 (double)
numeric string "12" 4.0 (double)
text "hello" 4.0 (double)
boolean true 4.0 (double)
typed date {"$date":"2026-01-15T15:00:00Z"} 4.0 (double)
empty array [] 4.0 (double)
numeric array [1,2,3] 4.0 (double)
object {"x":1} 4.0 (double)
null null 2.0 (double)
missing Field absent 2.0 (double)
decimal 2.5 2.25 (double)
numeric string "12" 2.0 (double)
text "hello" 2.0 (double)
boolean true 2.0 (double)
typed date {"$date":"2026-01-15T15:00:00Z"} 2.0 (double)
empty array [] 2.0 (double)
numeric array [1,2,3] 2.0 (double)
object {"x":1} 2.0 (double)

Argument handling

Invocation Result
{"$avg":[]} null
{"$avg":{"unexpected":1}} null

Examples

Expression: 

{
  "$avg": [
    2,
    4
  ]
}

Input document: 

{}

Observed SrotaX result: 3.0 (double).

Detailed input cases

Expand the complete argument-by-argument test matrix

Each table changes only the indicated argument from the example above. Other arguments retain their baseline values. Values normally come from the input field probe; literal configuration arguments are replaced directly. “Missing” means the field is absent, not explicitly null. Numeric strings are strings, not numbers.

Argument: number[0]

Input case Supplied value SrotaX result
null null 4.0 (double)
missing Field absent 4.0 (double)
zero 0 2.0 (double)
negative -2 1.0 (double)
decimal 2.5 3.25 (double)
numeric string "12" 4.0 (double)
text "hello" 4.0 (double)
empty string "" 4.0 (double)
boolean true 4.0 (double)
false false 4.0 (double)
typed date {"$date":"2026-01-15T15:00:00Z"} 4.0 (double)
decimal128 {"$numberDecimal":"1.25"} 2.625 (double)
empty array [] 4.0 (double)
numeric array [1,2,3] 4.0 (double)
mixed array [1,null,"x",3] 4.0 (double)
nested array [[1,2],[3]] 4.0 (double)
empty object {} 4.0 (double)
object {"x":1} 4.0 (double)
ISO date string "2026-01-15T15:00:00Z" 4.0 (double)

Argument: number[1]

Input case Supplied value SrotaX result
null null 2.0 (double)
missing Field absent 2.0 (double)
zero 0 1.0 (double)
negative -2 0.0 (double)
decimal 2.5 2.25 (double)
numeric string "12" 2.0 (double)
text "hello" 2.0 (double)
empty string "" 2.0 (double)
boolean true 2.0 (double)
false false 2.0 (double)
typed date {"$date":"2026-01-15T15:00:00Z"} 2.0 (double)
decimal128 {"$numberDecimal":"1.25"} 1.625 (double)
empty array [] 2.0 (double)
numeric array [1,2,3] 2.0 (double)
mixed array [1,null,"x",3] 2.0 (double)
nested array [[1,2],[3]] 2.0 (double)
empty object {} 2.0 (double)
object {"x":1} 2.0 (double)
ISO date string "2026-01-15T15:00:00Z" 2.0 (double)

Argument: single array expression

Input case Supplied value SrotaX result
single operand null null null
single operand missing Field absent null
single operand zero 0 0.0 (double)
single operand negative -2 -2.0 (double)
single operand decimal 2.5 2.5 (double)
single operand numeric string "12" null
single operand text "hello" null
single operand empty string "" null
single operand boolean true null
single operand false false null
single operand typed date {"$date":"2026-01-15T15:00:00Z"} null
single operand decimal128 {"$numberDecimal":"1.25"} 1.25 (double)
single operand empty array [] null
single operand numeric array [1,2,3] 2.0 (double)
single operand mixed array [1,null,"x",3] 2.0 (double)
single operand nested array [[1,2],[3]] null
single operand empty object {} null
single operand object {"x":1} null
single operand ISO date string "2026-01-15T15:00:00Z" null

Verification

This page records 60 executed cases. It covers individual argument substitutions, not every cross-product of arguments, locale, daylight-saving transitions, numeric overflow, collation or resource limits. No untested behavior is guaranteed.

Download exact expressions, inputs and SrotaX results. Errors are observed messages, not stable public error codes. The reference generator reads the checked-in execution report; do not edit generated observations by hand.

MongoDB differences

Compared with MongoDB 9.0.4: 57 exact BSON matches, 0 both rejected, 3 value/type/acceptance differences, 0 object-field-order differences.

“Exact” includes numeric BSON types and object key order. A value of 3 as int32 differs from 3.0 as double. Object-field-order differences are reported separately; object key ordering is not enforced by the engine regression baseline. Both rejected does not mean the error codes or messages match. This is finite-case evidence, not full compatibility certification.

Show observed differences
Tested case SrotaX MongoDB
number[0] / decimal128 2.625 (double) 2.625 (decimal128)
number[1] / decimal128 1.625 (double) 1.625 (decimal128)
single array expression / single operand decimal128 1.25 (double) 1.25 (decimal128)

Download full comparison evidence.