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$zip

Definition

Combines corresponding elements of input arrays.

Expression operator · Arrays · Studio Visual: not exposed. Studio validates the complete expression separately.

Syntax

{
  "$zip": {
    "inputs": <inputs>,
    "useLongestLength": <useLongestLength>
  }
}

Replace angle-bracket placeholders with expressions or values.

Optional parameters may be omitted.

Parameters

Parameter Required Description
inputs Yes Array of expressions, each resolving to an array to combine by position.
useLongestLength No Literal boolean. Defaults to false (shortest input); true uses the longest input and pads shorter inputs.

defaults is also accepted by Core as a literal array of padding values, one per input array. It is used only with useLongestLength: true; missing padding entries use null. This option is not listed by the current Visual catalog.

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 inputs argument:

Input case Supplied value Result
null null Error — $zip inputs must be array of arrays and useLongestLength a boolean
missing Field absent Error — $zip inputs must be array of arrays and useLongestLength a boolean
decimal 2.5 Error — $zip inputs must be array of arrays and useLongestLength a boolean
numeric string "12" Error — $zip inputs must be array of arrays and useLongestLength a boolean
text "hello" Error — $zip inputs must be array of arrays and useLongestLength a boolean
boolean true Error — $zip inputs must be array of arrays and useLongestLength a boolean
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $zip inputs must be array of arrays and useLongestLength a boolean
empty array [] Error — Index 0 out of bounds for length 0
numeric array [1,2,3] Error — class java.lang.Integer cannot be cast to class java.util.List (java.lang.Integer and java.util.List are in module java.base of loader 'bootstrap')
object {"x":1} Error — $zip inputs must be array of arrays and useLongestLength a boolean

Argument handling

Invocation Result
{"$zip":[]} Error — $zip expects an object with 'inputs', optional 'useLongestLength'
{"$zip":{"unexpected":1}} Error — $zip inputs must be array of arrays and useLongestLength a boolean

Examples

Expression: 

{
  "$zip": {
    "inputs": [
      [
        1
      ],
      [
        2
      ]
    ]
  }
}

Input document: 

{}

Observed SrotaX result: [[1,2]].

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: inputs

Input case Supplied value SrotaX result
null null Error — $zip inputs must be array of arrays and useLongestLength a boolean
missing Field absent Error — $zip inputs must be array of arrays and useLongestLength a boolean
zero 0 Error — $zip inputs must be array of arrays and useLongestLength a boolean
negative -2 Error — $zip inputs must be array of arrays and useLongestLength a boolean
decimal 2.5 Error — $zip inputs must be array of arrays and useLongestLength a boolean
numeric string "12" Error — $zip inputs must be array of arrays and useLongestLength a boolean
text "hello" Error — $zip inputs must be array of arrays and useLongestLength a boolean
empty string "" Error — $zip inputs must be array of arrays and useLongestLength a boolean
boolean true Error — $zip inputs must be array of arrays and useLongestLength a boolean
false false Error — $zip inputs must be array of arrays and useLongestLength a boolean
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $zip inputs must be array of arrays and useLongestLength a boolean
decimal128 {"$numberDecimal":"1.25"} Error — $zip inputs must be array of arrays and useLongestLength a boolean
empty array [] Error — Index 0 out of bounds for length 0
numeric array [1,2,3] Error — class java.lang.Integer cannot be cast to class java.util.List (java.lang.Integer and java.util.List are in module java.base of loader 'bootstrap')
mixed array [1,null,"x",3] Error — class java.lang.Integer cannot be cast to class java.util.List (java.lang.Integer and java.util.List are in module java.base of loader 'bootstrap')
nested array [[1,2],[3]] [[1,3]]
empty object {} Error — $zip inputs must be array of arrays and useLongestLength a boolean
object {"x":1} Error — $zip inputs must be array of arrays and useLongestLength a boolean
ISO date string "2026-01-15T15:00:00Z" Error — $zip inputs must be array of arrays and useLongestLength a boolean
omitted named argument Argument removed Error — $zip inputs must be array of arrays and useLongestLength a boolean

Argument: useLongestLength

Input case Supplied value SrotaX result
null null Error — $zip inputs must be array of arrays and useLongestLength a boolean
zero 0 Error — $zip inputs must be array of arrays and useLongestLength a boolean
negative -2 Error — $zip inputs must be array of arrays and useLongestLength a boolean
decimal 2.5 Error — $zip inputs must be array of arrays and useLongestLength a boolean
numeric string "12" Error — $zip inputs must be array of arrays and useLongestLength a boolean
text "hello" Error — $zip inputs must be array of arrays and useLongestLength a boolean
empty string "" Error — $zip inputs must be array of arrays and useLongestLength a boolean
boolean true [[1,2]]
false false [[1,2]]
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $zip inputs must be array of arrays and useLongestLength a boolean
decimal128 {"$numberDecimal":"1.25"} Error — $zip inputs must be array of arrays and useLongestLength a boolean
empty array [] Error — $zip inputs must be array of arrays and useLongestLength a boolean
numeric array [1,2,3] Error — $zip inputs must be array of arrays and useLongestLength a boolean
mixed array [1,null,"x",3] Error — $zip inputs must be array of arrays and useLongestLength a boolean
nested array [[1,2],[3]] Error — $zip inputs must be array of arrays and useLongestLength a boolean
empty object {} Error — $zip inputs must be array of arrays and useLongestLength a boolean
object {"x":1} Error — $zip inputs must be array of arrays and useLongestLength a boolean
ISO date string "2026-01-15T15:00:00Z" Error — $zip inputs must be array of arrays and useLongestLength a boolean
omitted named argument Argument removed [[1,2]]

Verification

This page records 42 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: 4 exact BSON matches, 37 both rejected, 1 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
inputs / nested array [[1,3]] Error — Invalid $project :: caused by :: inputs must be an array of expressions, found string

Download full comparison evidence.