feat(associative): add objectFromKeys()

thi-ng · Aug 21, 2023 · 0a6ba5f · 0a6ba5f
1 parent 1d6d661
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diff --git a/packages/associative/src/from-keys.ts b/packages/associative/src/from-keys.ts
@@ -0,0 +1,34 @@
+import type { Fn } from "@thi.ng/api";
+import { isFunction } from "@thi.ng/checks/is-function";
+
+/**
+ * Similar to (but much faster than) `Object.fromEntries()`. Takes an array of
+ * property keys and an `init` value or function. If the latter, the `init`
+ * function is called for each key and its results are used as values. Otherwise
+ * the `init` value is used homogeneously for all keys.
+ *
+ * @example
+ * ```ts
+ * objectFromKeys(["a", "b", "c"], 1)
+ * // { a: 1, b: 1, c: 1 }
+ *
+ * objectFromKeys(["a", "b", "c"], () => [])
+ * // { a: [], b: [], c: [] }
+ *
+ * objectFromKeys(["a", "b", "c"], (k) => `${k}-${(Math.random()*100)|0}`)
+ * // { a: 'a-54', b: 'b-8', c: 'c-61' }
+ * ```
+ *
+ * @param keys
+ * @param init
+ */
+export const objectFromKeys = <K extends PropertyKey, V>(
+	keys: K[],
+	init: V | Fn<K, V>
+) =>
+	keys.reduce(
+		isFunction(init)
+			? (acc, k) => ((acc[k] = init(k)), acc)
+			: (acc, k) => ((acc[k] = init), acc),
+		<Record<K, V>>{}
+	);
diff --git a/packages/associative/src/index.ts b/packages/associative/src/index.ts
@@ -9,6 +9,7 @@ export * from "./dissoc.js";
 export * from "./empty.js";
 export * from "./equiv-map.js";
 export * from "./first.js";
+export * from "./from-keys.js";
 export * from "./hash-map.js";
 export * from "./indexed.js";
 export * from "./intersection.js";