fix: groupBy types

.changeset/slimy-countries-look.md

@@ -0,0 +1,5 @@
+---
+"@opentf/utils": minor
+---
+
+Fixed groupBy types.

packages/utils/__tests__/array/groupBy.spec.js → packages/utils/__tests__/array/groupBy.spec.ts

@@ -24,9 +24,29 @@ describe('Array', () => {
         v % 2 === 0 ? 'Even' : 'Odd'
       )
     ).toEqual({ Even: [2, 4, 6, 8], Odd: [1, 3, 5, 7, 9] });
+
     expect(groupBy(['one', 'two', 'three'], 'length')).toEqual({
       3: ['one', 'two'],
       5: ['three'],
     });
+
+    const inventory = [
+      { name: 'asparagus', type: 'vegetables', quantity: 5 },
+      { name: 'bananas', type: 'fruit', quantity: 0 },
+      { name: 'goat', type: 'meat', quantity: 23 },
+      { name: 'cherries', type: 'fruit', quantity: 5 },
+      { name: 'fish', type: 'meat', quantity: 22 },
+    ];
+    expect(groupBy(inventory, ({ type }) => type)).toEqual({
+      vegetables: [{ name: 'asparagus', type: 'vegetables', quantity: 5 }],
+      fruit: [
+        { name: 'bananas', type: 'fruit', quantity: 0 },
+        { name: 'cherries', type: 'fruit', quantity: 5 },
+      ],
+      meat: [
+        { name: 'goat', type: 'meat', quantity: 23 },
+        { name: 'fish', type: 'meat', quantity: 22 },
+      ],
+    });
   });
 });

packages/utils/src/array/groupBy.ts

@@ -1,10 +1,13 @@
-export type GroupKey = (a: unknown) => string | string;
+export type GroupKey<T> = ((a: T) => string) | string;
 
-export default function groupBy(arr: unknown[], key: GroupKey) {
-  return arr.reduce((acc: Record<string, unknown>, obj) => {
+export default function groupBy<T>(
+  arr: T[],
+  key: GroupKey<T>
+): Record<string, T[]> {
+  return arr.reduce((acc: Record<string, T[]>, obj: T) => {
     const k =
-      typeof key === 'function' ? key(obj) : (obj as Iterable<unknown>)[key];
+      typeof key === 'function' ? key(obj) : (obj[key as keyof T] as string);
     const curGroup = acc[k] ?? [];
-    return { ...acc, [k]: [...(curGroup as unknown[]), obj] };
+    return { ...acc, [k]: [...curGroup, obj] };
   }, {});
 }