feat(collections): add minWith (#1169)

collections/README.md

@@ -524,6 +524,21 @@ console.assert(
 );
 ```
 
+### minWith
+
+Returns the first element having the smallest value according to the provided
+comparator or undefined if there are no elements
+
+```ts
+import { minWith } from "https://deno.land/std@$STD_VERSION/collections/mod.ts";
+import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
+
+const people = ["Kim", "Anna", "John"];
+const smallestName = minWith(people, (a, b) => a.length - b.length);
+
+assertEquals(smallestName, "Kim");
+```
+
 ### includesValue
 
 If the given value is part of the given object it returns true, otherwise it

collections/min_with.ts

@@ -0,0 +1,31 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+/**
+ * Returns the first element having the smallest value according to the provided comparator or undefined if there are no elements
+ *
+ * Example:
+ *
+ * ```ts
+ * import { minWith } from "./min_with.ts";
+ * import { assertEquals } from "../testing/asserts.ts";
+ *
+ * const people = ["Kim", "Anna", "John"];
+ * const smallestName = minWith(people, (a, b) => a.length - b.length);
+ *
+ * assertEquals(smallestName, "Kim");
+ * ```
+ */
+export function minWith<T>(
+  array: readonly T[],
+  comparator: (a: T, b: T) => number,
+): T | undefined {
+  let min: T | undefined = undefined;
+
+  for (const current of array) {
+    if (min === undefined || comparator(current, min) < 0) {
+      min = current;
+    }
+  }
+
+  return min;
+}

collections/min_with_test.ts

@@ -0,0 +1,71 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals } from "../testing/asserts.ts";
+import { minWith } from "./min_with.ts";
+
+function minWithTest<T>(
+  input: [T[], (a: T, b: T) => number],
+  expected: T | undefined,
+  message?: string,
+) {
+  const actual = minWith(...input);
+  assertEquals(actual, expected, message);
+}
+
+Deno.test({
+  name: "[collections/minWith] no mutation",
+  fn() {
+    const input = [[1, 3], [6, 1, 3], [4]];
+    minWith(input, (a, b) => a.length - b.length);
+
+    assertEquals(input, [[1, 3], [6, 1, 3], [4]]);
+  },
+});
+
+Deno.test({
+  name: "[collections/minWith] empty input",
+  fn() {
+    minWithTest<string>([[], (a, b) => a.length - b.length], undefined);
+  },
+});
+
+Deno.test({
+  name: "[collections/minWith] array of arrays",
+  fn() {
+    minWithTest([[[1, 3], [6, 1, 3], [4]], (a, b) => a.length - b.length], [4]);
+  },
+});
+
+Deno.test({
+  name: "[collections/minWith] array of strings",
+  fn() {
+    minWithTest(
+      [["Kim", "Anna", "John"], (a, b) => a.length - b.length],
+      "Kim",
+    );
+  },
+});
+
+Deno.test({
+  name: "[collections/minWith] array of objects",
+  fn() {
+    minWithTest(
+      [
+        [
+          { name: "Kim", age: 24 },
+          { name: "Anna", age: 20 },
+          { name: "John", age: 43 },
+        ],
+        (a, b) => a.age - b.age,
+      ],
+      { name: "Anna", age: 20 },
+    );
+  },
+});
+
+Deno.test({
+  name: "[collections/minWith] duplicates",
+  fn() {
+    minWithTest([["John", "Kim", "Kim"], (a, b) => a.length - b.length], "Kim");
+  },
+});

collections/mod.ts

@@ -29,6 +29,7 @@ export * from "./union.ts";
 export * from "./without_all.ts";
 export * from "./unzip.ts";
 export * from "./zip.ts";
+export * from "./min_with.ts";
 export * from "./includes_value.ts";
 export * from "./take_last_while.ts";
 export * from "./take_while.ts";