diff --git a/packages/backend/src/misc/prelude/array.ts b/packages/backend/src/misc/prelude/array.ts
index dbfe1fff18..f741a0c913 100644
--- a/packages/backend/src/misc/prelude/array.ts
+++ b/packages/backend/src/misc/prelude/array.ts
@@ -65,44 +65,6 @@ export function maximum(xs: number[]): number {
 	return Math.max(...xs);
 }
 
-/**
- * Splits an array based on the equivalence relation.
- * The concatenation of the result is equal to the argument.
- */
-export function groupBy<T>(f: EndoRelation<T>, xs: T[]): T[][] {
-	const groups = [] as T[][];
-	for (const x of xs) {
-		const lastGroup = groups.at(-1);
-		if (lastGroup !== undefined && f(lastGroup[0], x)) {
-			lastGroup.push(x);
-		} else {
-			groups.push([x]);
-		}
-	}
-	return groups;
-}
-
-/**
- * Splits an array based on the equivalence relation induced by the function.
- * The concatenation of the result is equal to the argument.
- */
-export function groupOn<T, S>(f: (x: T) => S, xs: T[]): T[][] {
-	return groupBy((a, b) => f(a) === f(b), xs);
-}
-
-export function groupByX<T>(collections: T[], keySelector: (x: T) => string) {
-	return collections.reduce((obj: Record<string, T[]>, item: T) => {
-		const key = keySelector(item);
-		if (!Object.prototype.hasOwnProperty.call(obj, key)) {
-			obj[key] = [];
-		}
-
-		obj[key].push(item);
-
-		return obj;
-	}, {});
-}
-
 /**
  * Compare two arrays by lexicographical order
  */
diff --git a/packages/frontend/src/scripts/array.ts b/packages/frontend/src/scripts/array.ts
index b3d76e149f..f2feb29dfc 100644
--- a/packages/frontend/src/scripts/array.ts
+++ b/packages/frontend/src/scripts/array.ts
@@ -77,44 +77,6 @@ export function maximum(xs: number[]): number {
 	return Math.max(...xs);
 }
 
-/**
- * Splits an array based on the equivalence relation.
- * The concatenation of the result is equal to the argument.
- */
-export function groupBy<T>(f: EndoRelation<T>, xs: T[]): T[][] {
-	const groups = [] as T[][];
-	for (const x of xs) {
-		const lastGroup = groups.at(-1);
-		if (lastGroup !== undefined && f(lastGroup[0], x)) {
-			lastGroup.push(x);
-		} else {
-			groups.push([x]);
-		}
-	}
-	return groups;
-}
-
-/**
- * Splits an array based on the equivalence relation induced by the function.
- * The concatenation of the result is equal to the argument.
- */
-export function groupOn<T, S>(f: (x: T) => S, xs: T[]): T[][] {
-	return groupBy((a, b) => f(a) === f(b), xs);
-}
-
-export function groupByX<T>(collections: T[], keySelector: (x: T) => string) {
-	return collections.reduce((obj: Record<string, T[]>, item: T) => {
-		const key = keySelector(item);
-		if (typeof obj[key] === 'undefined') {
-			obj[key] = [];
-		}
-
-		obj[key].push(item);
-
-		return obj;
-	}, {});
-}
-
 /**
  * Compare two arrays by lexicographical order
  */