feat(asyncMapKeyFirstByOnce): add asyncMapKeyFirstByOnce function

Author: djcsdy

index.test.ts

@@ -31,6 +31,7 @@ import {
     asyncKeyLastByOnce,
     asyncLastOnce,
     asyncMapKeyByOnce,
+    asyncMapKeyFirstByOnce,
     asyncMapOnce,
     asyncMaximumByOnce,
     asyncMaximumOnce,
@@ -682,3 +683,13 @@ test("asyncMapKeyByOnce", async t => {
     t.deepEqual(map.get("odd"), ["1", "3", "5"]);
     t.deepEqual(Array.from(map.keys()), ["odd", "even"]);
 });
+
+test("asyncMapKeyFirstByOnce", async t => {
+    const map = await asyncMapKeyFirstByOnce(asyncIterator([1, 3, 4, 2, 5, 6]), e => [
+        e % 2 === 0 ? "even" : "odd",
+        String(e)
+    ]);
+    t.is(map.get("even"), "4");
+    t.is(map.get("odd"), "1");
+    t.deepEqual(Array.from(map.keys()), ["odd", "even"]);
+});

index.ts

@@ -1300,4 +1300,35 @@ export function asyncMapKeyByOnceFn<TKey, TElement, TNewElement>(
     ) => readonly [TKey, TNewElement] | Promise<readonly [TKey, TNewElement]>
 ): (iterator: AsyncIteratorLike<TElement>) => Promise<Map<TKey, readonly TNewElement[]>> {
     return async iterator => asyncMapKeyByOnce(iterator, f);
-}
+}
+
+export async function asyncMapKeyFirstByOnce<TKey, TElement, TNewElement>(
+    iterator: AsyncIteratorLike<TElement>,
+    f: (
+        element: TElement,
+        index: number
+    ) => readonly [TKey, TNewElement] | Promise<readonly [TKey, TNewElement]>
+): Promise<Map<TKey, TNewElement>> {
+    const it = asyncIterator(iterator);
+    const map = new Map<TKey, TNewElement>();
+    for (
+        let i = 0, element = await it.next();
+        element.done !== true;
+        ++i, element = await it.next()
+    ) {
+        const [key, value] = await f(element.value, i);
+        if (!map.has(key)) {
+            map.set(key, value);
+        }
+    }
+    return map;
+}
+
+export function asyncMapKeyFirstByOnceFn<TKey, TElement, TNewElement>(
+    f: (
+        element: TElement,
+        index: number
+    ) => readonly [TKey, TNewElement] | Promise<readonly [TKey, TNewElement]>
+): (iterator: AsyncIteratorLike<TElement>) => Promise<Map<TKey, TNewElement>> {
+    return async iterator => asyncMapKeyFirstByOnce(iterator, f);
+}