From 0d6a88826182bb6f767eb8dee7d77ec42e2839a4 Mon Sep 17 00:00:00 2001
From: Sergei Zharinov <zharinov@users.noreply.github.com>
Date: Fri, 7 Jul 2023 20:04:11 +0300
Subject: [PATCH] feat: Add `filterMap` utility for fast array transforms
(#23252)
---
lib/util/filter-map.spec.ts | 17 +++++++++++++++++
lib/util/filter-map.ts | 26 ++++++++++++++++++++++++++
2 files changed, 43 insertions(+)
create mode 100644 lib/util/filter-map.spec.ts
create mode 100644 lib/util/filter-map.ts
diff --git a/lib/util/filter-map.spec.ts b/lib/util/filter-map.spec.ts
new file mode 100644
index 0000000000..2c198ace4c
--- /dev/null
+++ b/lib/util/filter-map.spec.ts
@@ -0,0 +1,17 @@
+import { filterMap } from './filter-map';
+
+describe('util/filter-map', () => {
+ it('should return an empty array when given an empty array', () => {
+ const input: unknown[] = [];
+ const output = filterMap(input, () => 42);
+ expect(output).toBe(input);
+ expect(output).toBeEmpty();
+ });
+
+ it('should return an array with only the mapped values that pass the filter', () => {
+ const input = [0, 1, 2, 3, 4];
+ const output = filterMap(input, (n) => n * n);
+ expect(output).toBe(input);
+ expect(output).toEqual([1, 4, 9, 16]);
+ });
+});
diff --git a/lib/util/filter-map.ts b/lib/util/filter-map.ts
new file mode 100644
index 0000000000..705d8656d0
--- /dev/null
+++ b/lib/util/filter-map.ts
@@ -0,0 +1,26 @@
+import is from '@sindresorhus/is';
+
+type Falsy = false | '' | 0 | 0n | null | undefined;
+
+/**
+ * Filter and map an array *in place* with single iteration.
+ */
+export function filterMap<T, U>(array: T[], fn: (item: T) => Falsy | U): U[] {
+ const length = array.length;
+ let newIdx = 0;
+ for (let oldIdx = 0; oldIdx < length; oldIdx += 1) {
+ const item = array[oldIdx];
+ const res = fn(item);
+ if (is.truthy(res)) {
+ array[newIdx] = res as never;
+ newIdx += 1;
+ }
+ }
+
+ const deletedCount = length - newIdx;
+ if (deletedCount) {
+ array.length = length - deletedCount;
+ }
+
+ return array as never;
+}
--
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