$slice
Definition
Extracts an array segment; negative indexes are not Mongo-compatible.
Expression operator · Arrays · Studio Visual: available. Studio validates the complete expression separately.
Syntax
{ "$slice": [ <array>, <positionOrCount>, <count> ] }
Replace angle-bracket placeholders with expressions or values.
Optional parameters may be omitted.
Parameters
| Parameter | Required | Description |
|---|---|---|
array |
Yes | Expression supplying the source array. |
positionOrCount |
Yes | With two arguments, the number of elements to keep. With three arguments, the starting position. |
count |
No | Number of elements to keep in the three-argument form. |
Arguments are positional: keep the order shown. The authoring signature accepts 2–3 arguments.
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 array argument:
| Input case | Supplied value | Result |
|---|---|---|
| null | null | Error — $slice expects first argument to be an array |
| missing | Field absent | Error — $slice expects first argument to be an array |
| decimal | 2.5 | Error — $slice expects first argument to be an array |
| numeric string | "12" | Error — $slice expects first argument to be an array |
| text | "hello" | Error — $slice expects first argument to be an array |
| boolean | true | Error — $slice expects first argument to be an array |
| typed date | {"$date":"2026-01-15T15:00:00Z"} | Error — $slice expects first argument to be an array |
| empty array | [] | Error — fromIndex(1) > toIndex(0) |
| numeric array | [1,2,3] | [2] |
| object | {"x":1} | Error — $slice expects first argument to be an array |
Argument handling
| Invocation | Result |
|---|---|
| {"$slice":[]} | Error — $slice expects [array, limit] or [array, skip, limit] |
| {"$slice":{"unexpected":1}} | Error — $slice expects [array, limit] or [array, skip, limit] |
Examples
Expression:
{
"$slice": [
[
1,
2,
3
],
1,
1
]
}
Input document:
{}
Observed SrotaX result: [2].
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: array[0]
| Input case | Supplied value | SrotaX result |
|---|---|---|
| null | null | Error — $slice expects first argument to be an array |
| missing | Field absent | Error — $slice expects first argument to be an array |
| zero | 0 | Error — $slice expects first argument to be an array |
| negative | -2 | Error — $slice expects first argument to be an array |
| decimal | 2.5 | Error — $slice expects first argument to be an array |
| numeric string | "12" | Error — $slice expects first argument to be an array |
| text | "hello" | Error — $slice expects first argument to be an array |
| empty string | "" | Error — $slice expects first argument to be an array |
| boolean | true | Error — $slice expects first argument to be an array |
| false | false | Error — $slice expects first argument to be an array |
| typed date | {"$date":"2026-01-15T15:00:00Z"} | Error — $slice expects first argument to be an array |
| decimal128 | {"$numberDecimal":"1.25"} | Error — $slice expects first argument to be an array |
| empty array | [] | Error — fromIndex(1) > toIndex(0) |
| numeric array | [1,2,3] | [2] |
| mixed array | [1,null,"x",3] | [null] |
| nested array | [[1,2],[3]] | [[3]] |
| empty object | {} | Error — $slice expects first argument to be an array |
| object | {"x":1} | Error — $slice expects first argument to be an array |
| ISO date string | "2026-01-15T15:00:00Z" | Error — $slice expects first argument to be an array |
Argument: positionOrCount[1]
| Input case | Supplied value | SrotaX result |
|---|---|---|
| null | null | Error — $slice requires numeric skip/limit values |
| missing | Field absent | Error — $slice requires numeric skip/limit values |
| zero | 0 | [1] |
| negative | -2 | [] |
| decimal | 2.5 | [3] |
| numeric string | "12" | Error — $slice requires numeric skip/limit values |
| text | "hello" | Error — $slice requires numeric skip/limit values |
| empty string | "" | Error — $slice requires numeric skip/limit values |
| boolean | true | Error — $slice requires numeric skip/limit values |
| false | false | Error — $slice requires numeric skip/limit values |
| typed date | {"$date":"2026-01-15T15:00:00Z"} | Error — $slice requires numeric skip/limit values |
| decimal128 | {"$numberDecimal":"1.25"} | [2] |
| empty array | [] | Error — $slice requires numeric skip/limit values |
| numeric array | [1,2,3] | Error — $slice requires numeric skip/limit values |
| mixed array | [1,null,"x",3] | Error — $slice requires numeric skip/limit values |
| nested array | [[1,2],[3]] | Error — $slice requires numeric skip/limit values |
| empty object | {} | Error — $slice requires numeric skip/limit values |
| object | {"x":1} | Error — $slice requires numeric skip/limit values |
| ISO date string | "2026-01-15T15:00:00Z" | Error — $slice requires numeric skip/limit values |
Argument: count[2]
| Input case | Supplied value | SrotaX result |
|---|---|---|
| null | null | Error — $slice requires numeric skip/limit values |
| missing | Field absent | Error — $slice requires numeric skip/limit values |
| zero | 0 | [] |
| negative | -2 | [] |
| decimal | 2.5 | [2,3] |
| numeric string | "12" | Error — $slice requires numeric skip/limit values |
| text | "hello" | Error — $slice requires numeric skip/limit values |
| empty string | "" | Error — $slice requires numeric skip/limit values |
| boolean | true | Error — $slice requires numeric skip/limit values |
| false | false | Error — $slice requires numeric skip/limit values |
| typed date | {"$date":"2026-01-15T15:00:00Z"} | Error — $slice requires numeric skip/limit values |
| decimal128 | {"$numberDecimal":"1.25"} | [2] |
| empty array | [] | Error — $slice requires numeric skip/limit values |
| numeric array | [1,2,3] | Error — $slice requires numeric skip/limit values |
| mixed array | [1,null,"x",3] | Error — $slice requires numeric skip/limit values |
| nested array | [[1,2],[3]] | Error — $slice requires numeric skip/limit values |
| empty object | {} | Error — $slice requires numeric skip/limit values |
| object | {"x":1} | Error — $slice requires numeric skip/limit values |
| ISO date string | "2026-01-15T15:00:00Z" | Error — $slice requires numeric skip/limit values |
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: 5 exact BSON matches, 41 both rejected, 14 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 |
|---|---|---|
| array[0] / null | Error — $slice expects first argument to be an array | null |
| array[0] / missing | Error — $slice expects first argument to be an array | null |
| array[0] / empty array | Error — fromIndex(1) > toIndex(0) | [] |
| positionOrCount[1] / null | Error — $slice requires numeric skip/limit values | null |
| positionOrCount[1] / missing | Error — $slice requires numeric skip/limit values | null |
| positionOrCount[1] / negative | [] | [2] |
| positionOrCount[1] / decimal | [3] | Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: Second argument to $slice can't be represented as a 32-bit i |
| positionOrCount[1] / decimal128 | [2] | Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: Second argument to $slice can't be represented as a 32-bit i |
| count[2] / null | Error — $slice requires numeric skip/limit values | null |
| count[2] / missing | Error — $slice requires numeric skip/limit values | null |
| count[2] / zero | [] | Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: Third argument to $slice must be positive: 0 |
| count[2] / negative | [] | Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: Third argument to $slice must be positive: -2 |
| count[2] / decimal | [2,3] | Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: Third argument to $slice can't be represented as a 32-bit in |
| count[2] / decimal128 | [2] | Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: Third argument to $slice can't be represented as a 32-bit in |