Merge pull request bids-standard#261 from drammock/feat/unique

feat: add unique() function for expressions

Author: effigies

changelog.d/20250916_145237_dan_unique.md

@@ -0,0 +1,47 @@
+<!--
+A new scriv changelog fragment.
+
+Uncomment the section that is right (remove the HTML comment wrapper).
+For top level release notes, leave all the headers commented out.
+-->
+
+### Added
+
+- Add support for the `unique()` function in schema expressions.
+
+<!--
+### Changed
+
+- A bullet item for the Changed category.
+
+-->
+<!--
+### Fixed
+
+- A bullet item for the Fixed category.
+
+-->
+<!--
+### Deprecated
+
+- A bullet item for the Deprecated category.
+
+-->
+<!--
+### Removed
+
+- A bullet item for the Removed category.
+
+-->
+<!--
+### Security
+
+- A bullet item for the Security category.
+
+-->
+<!--
+### Infrastructure
+
+- A bullet item for the Infrastructure category.
+
+-->

src/schema/expressionLanguage.ts

@@ -90,6 +90,12 @@ export const expressionFunctions = {
     }
     return null
   },
+  unique: <T>(list: T[]): T[] | null => {
+    if (list !== null) {
+        return [...new Set(list)]
+    }
+    return null
+  },
   count: <T>(list: T[], val: T): number => {
     return list.filter((x) => x === val).length
   },