feat(array/average, array/sortAsc, array/sortDesc): new features

src/array/nth-items.js

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+/**
+ * Returns a new array which contains every n-th item of the original array.
+ * @param {Array} arr 
+ * @param {Number} pos, position to look for 
+ * @returns {Array}
+ */
+const fn = (arr, pos) => arr.filter((arr, index) => index % pos === pos - 1);
+
+export default fn;

src/array/sort-asc.js

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+/**
+ * Returns a new array sorted by ascending order (Numbers). 
+ * Beware of JavaScript's Automatic Type Conversion if your `Array` contains something else than `Numbers`.
+ * @param {Array} arr 
+ * @returns {Array}
+ */
+
+const fn = arr => [...arr].sort((a, b) => a - b);
+
+export default fn;

src/array/sort-desc.js

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+/**
+ * Returns a new array sorted by descending order (Numbers).
+ * Beware of JavaScript's Automatic Type Conversion if your `Array` contains something else than `Numbers`.
+ * @param {Array} arr 
+ * @returns {Array}
+ */
+
+const fn = arr => [...arr].sort((a, b) => a - b).reverse();
+
+export default fn;

test/array/nth-items.spec.js

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+import { nthItems } from '../../src/array';
+const test = require('ava');
+
+let input;
+test.beforeEach(t => {
+    input = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];
+})
+
+test('returns every item at n-th = 1', t => {
+    let position = 1;
+    let expectation = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+test('returns every item at n-th = 2', t => {
+    let position = 2;
+    let expectation = [2, 4, 6, 8, 10, 12, 14, 16, 18, 20];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+test('returns every item at n-th = 3', t => {
+    let position = 3;
+    let expectation = [3, 6, 9, 12, 15, 18];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+test('returns every item at n-th = 4', t => {
+    let position = 4;
+    let expectation = [4, 8, 12, 16, 20];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+test('returns every item at n-th = 5', t => {
+    let position = 5;
+    let expectation = [5, 10, 15, 20];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+test('returns every item at n-th = 6', t => {
+    let position = 6;
+    let expectation = [6, 12, 18];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+test('returns every item at n-th = 7', t => {
+    let position = 7;
+    let expectation = [7, 14];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+
+test('returns every item at n-th = 8', t => {
+    let position = 8;
+    let expectation = [8, 16];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+
+
+test('returns every item at n-th = 9', t => {
+    let position = 9;
+    let expectation = [9, 18];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+
+test('returns every item at n-th = 10', t => {
+    let position = 10;
+    let expectation = [10, 20];
+    t.deepEqual(nthItems(input, position), expectation);
+});
+
+
+
+
+

test/array/sort-asc.spec.js

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+import { sortAsc } from '../../src/array';
+const test = require('ava');
+
+let input;
+test.beforeEach(t => {
+    input = [4, 2, 1, 0, 3];
+})
+
+test('returns a new array array', t => {
+    let arr = [1, 2, 3, 4];
+    t.not(sortAsc(arr), arr);
+});
+
+test('returns a new array array sorted by ascending order', t => {
+    let expectation = [0, 1, 2, 3, 4];
+    t.deepEqual(sortAsc(input), expectation);
+});

test/array/sort-desc.spec.js

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+import { sortDesc } from '../../src/array';
+const test = require('ava');
+
+let input;
+test.beforeEach(t => {
+    input = [4, 2, 1, 0, 3];
+})
+
+test('returns a new array array', t => {
+    let arr = [4, 3, 2, 1, 0];
+    t.not(sortDesc(arr), arr);
+});
+
+test('returns a new array array sorted by ascending order', t => {
+    let expectation = [4, 3, 2, 1, 0];
+    t.deepEqual(sortDesc(input), expectation);
+});