Implement reduceBy helper

Author: NoelDeMartin

src/helpers/array_helpers.test.ts

@@ -22,6 +22,7 @@ import {
     arrayWithout,
     arrayWithoutIndexes,
     arrayZip,
+    reduceBy,
 } from './array_helpers';
 
 describe('Array helpers', () => {
@@ -256,6 +257,34 @@ describe('Array helpers', () => {
         expect(arrayFrom(null, true)).toEqual([]);
     });
 
+    it('reduces by key', () => {
+        const items = [
+            { id: '1', name: 'Alice' },
+            { id: '2', name: 'Bob' },
+        ];
+
+        const result = reduceBy(items, 'id');
+
+        expect(result).toEqual({
+            1: { id: '1', name: 'Alice' },
+            2: { id: '2', name: 'Bob' },
+        });
+    });
+
+    it('reduces by key with projection', () => {
+        const items = [
+            { id: '1', name: 'Alice' },
+            { id: '2', name: 'Bob' },
+        ];
+
+        const result = reduceBy(items, 'id', (item) => item.name);
+
+        expect(result).toEqual({
+            1: 'Alice',
+            2: 'Bob',
+        });
+    });
+
 });
 
 let enabled: boolean | undefined;

src/helpers/array_helpers.ts

@@ -310,3 +310,24 @@ export function arrayFrom<T>(value: T, ignoreEmptyValues: boolean = false): Arra
 export function range(length: number): number[] {
     return Array.from({ length }, (_, item) => item);
 }
+
+export function reduceBy<TItem, TKey extends keyof TItem, TProjection>(
+    items: TItem[],
+    key: TKey,
+    project: (item: TItem) => TProjection
+): Partial<Record<string, TProjection>>;
+export function reduceBy<TItem, TKey extends keyof TItem>(items: TItem[], key: TKey): Partial<Record<string, TItem>>;
+export function reduceBy<TItem, TKey extends keyof TItem, TProjection>(
+    items: TItem[],
+    key: TKey,
+    project?: (item: TItem) => TProjection,
+): Partial<Record<string, TProjection>> {
+    return items.reduce(
+        (acc, item) => {
+            acc[toString(item[key])] = project ? project(item) : (item as unknown as TProjection);
+
+            return acc;
+        },
+        {} as Partial<Record<string, TProjection>>,
+    );
+}