The `in` Operator

The in operator tests whether a value is a member of an array. It is the simplest way to check list membership in JSONata and appears throughout DAQS rules — in filter predicates, category exclusion lists, and GUID matching.

Syntax

value in array

Returns true if value is equal to any element in array, false otherwise.

In a filter predicate

$CategoryExclusion := ["OST_DetailComponents", "OST_Furniture"];

$[type = "FamilySymbol"
  and $not(values.category.label in $CategoryExclusion)
]

in works directly inside [ ] filter predicates — no function call needed.

Checking parent membership

When filtering instances by a set of symbol IDs:

(
  $symbolIds := $[type = "FamilySymbol" and values.assemblyCode = "21.10"].id;

  $[type = "FamilyInstance" and parent.id in $symbolIds].{
    "id": id,
    "name": name
  }
)

$symbolIds is an array of numbers. parent.id in $symbolIds checks whether the instance's parent is in that set.

Checking GUID membership

Used when filtering Parameter objects to only those relevant to the current rule:

$paramGuids := {
  "NLRS_C_kwaliteitsklasse_code": "73803e29-3501-4c39-8c13-a49c4f2259d3"
};

$$[type = "Parameter" and values.guid in $paramGuids.*]

$paramGuids.* selects all values from the $paramGuids object — producing an array of GUIDs. The filter then keeps only Parameter objects whose GUID appears in that list.

`in` vs `$arrayContains()`

	`in`	`$arrayContains()`
Input	Static or variable array	Any expression
Works with dynamic arrays?	Yes	Yes
Readable	Yes	Less so
Standard JSONata	Yes	Custom function

Use in whenever possible. $arrayContains() (built with $sum + $map) is only needed when in cannot be applied — for example, when testing whether an element exists in a nested or computed structure that in cannot traverse.

Common mistakes

Using in on a single value instead of an array — "abc" in "abc" returns false; the right side must be an array
Assuming in is case-insensitive — it is not; "OST_Doors" in ["ost_doors"] returns false
Forgetting $paramGuids.* when checking GUIDs — values.guid in $paramGuids checks membership in the object itself (always false); you need $paramGuids.* to get the array of values

The in Operator