feat(collections): add sumOf

collections/mod.ts

@@ -14,3 +14,4 @@ export * from "./map_keys.ts";
 export * from "./map_values.ts";
 export * from "./partition.ts";
 export * from "./permutations.ts";
+export * from "./sum_of.ts";

collections/sum_of.ts

@@ -0,0 +1,35 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+import { Selector } from "./types.ts";
+
+/**
+ * Applies the given selector to all elements in the given collection and calculates the sum of the results
+ *
+ * Example:
+ *
+ * ```typescript
+ * import { sumOf } from "./sum_of.ts"
+ *
+ * const people = [
+ *     { name: 'Anna', age: 34 },
+ *     { name: 'Kim', age: 42 },
+ *     { name: 'John', age: 23 },
+ * ]
+ * const totalAge = sumOf(people, i => i.age)
+ *
+ * console.assert(totalAge === 99)
+ * ```
+ */
+export function sumOf<T>(
+  array: Array<T>,
+  selector: Selector<T, number>,
+): number {
+  const selected = array.map(selector);
+  let sum = 0;
+
+  for (const i of selected) {
+    sum += i;
+  }
+
+  return sum;
+}

collections/sum_of_test.ts

@@ -0,0 +1,88 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals } from "../testing/asserts.ts";
+import { sumOf } from "./sum_of.ts";
+
+Deno.test("[collections/sumOf] On object properties", () => {
+  const object = [
+    { name: "Kyle", age: 34 },
+    { name: "John", age: 42 },
+    { name: "Anna", age: 23 },
+  ];
+
+  const actual = sumOf(object, (i) => i.age);
+
+  assertEquals(actual, 99);
+});
+
+Deno.test("[collections/sumOf] Add 2 to each num", () => {
+  const array = [1, 2, 3];
+
+  const actual = sumOf(array, (i) => i + 2);
+
+  assertEquals(actual, 12);
+});
+
+Deno.test("[collections/sumOf] Regular sum", () => {
+  const array = [1, 2, 3];
+
+  const actual = sumOf(array, (i) => i);
+
+  assertEquals(actual, 6);
+});
+
+Deno.test("[collections/sumOf] Negatives with regular sum", () => {
+  const array = [-1, -2, -3];
+
+  const actual = sumOf(array, (i) => i);
+
+  assertEquals(actual, -6);
+});
+
+Deno.test("[collections/sumOf] Mixed negatives and positives with regular sum", () => {
+  const array = [-1, 2, 3, -5];
+
+  const actual = sumOf(array, (i) => i);
+
+  assertEquals(actual, -1);
+});
+
+Deno.test("[collections/sumBy] Selector turns nums into negatives", () => {
+  const array = [1, 3, 5, 3];
+
+  const actual = sumOf(array, (i) => i - 6);
+
+  assertEquals(actual, -12);
+});
+
+Deno.test("[collections/sumBy] Selector turns nums into zeros", () => {
+  const array = [3, 3, 3, 3];
+
+  const actual = sumOf(array, (i) => i - 3);
+
+  assertEquals(actual, 0);
+});
+
+Deno.test("[collections/sumOf] On negative object properties", () => {
+  const object = [
+    { name: "Kyle", age: -34 },
+    { name: "John", age: -42 },
+    { name: "Anna", age: -23 },
+  ];
+
+  const actual = sumOf(object, (i) => i.age);
+
+  assertEquals(actual, -99);
+});
+
+Deno.test("[collections/sumOf] On mixed object properties", () => {
+  const object = [
+    { name: "Kyle", age: -34 },
+    { name: "John", age: 42 },
+    { name: "Anna", age: -23 },
+  ];
+
+  const actual = sumOf(object, (i) => i.age);
+
+  assertEquals(actual, -15);
+});