feat(keyLastBy): add keyLastBy function

Author: djcsdy

index.test.ts

@@ -24,6 +24,7 @@ import {
     index,
     indexOf,
     initial,
+    keyLastBy,
     last,
     map,
     maximum,
@@ -384,3 +385,13 @@ test("zip", async t => {
         [3, 4]
     ]);
 });
+
+test("keyLastBy", async t => {
+    const map = await keyLastBy(asyncIterable([1, 3, 4, 2, 5, 6]), e =>
+        e % 2 === 0 ? "even" : "odd"
+    );
+    t.deepEqual(Array.from(map.entries()), [
+        ["odd", 5],
+        ["even", 6]
+    ]);
+});

index.ts

@@ -1016,3 +1016,25 @@ export function zipFn<T, U>(
 }
 
 export const asyncZipFn = zipFn;
+
+export async function keyLastBy<TKey, TElement>(
+    iterable: AsyncIterableLike<TElement>,
+    f: (element: TElement, index: number) => TKey
+): Promise<Map<TKey, TElement>> {
+    const map = new Map<TKey, TElement>();
+    let i = 0;
+    for await (const element of await iterable) {
+        map.set(f(element, i++), element);
+    }
+    return map;
+}
+
+export const asyncKeyLastBy = keyLastBy;
+
+export function keyLastByFn<TKey, TElement>(
+    f: (element: TElement, index: number) => TKey
+): (iterable: AsyncIterableLike<TElement>) => Promise<Map<TKey, TElement>> {
+    return async iterable => keyLastBy(iterable, f);
+}
+
+export const asyncKeyLastByFn = keyLastByFn;