Merge pull request #17 from giraugh/feat/rotateArray

Add array rotation method

.changeset/itchy-keys-tickle.md

@@ -0,0 +1,5 @@
+---
+"@giraugh/tools": minor
+---
+
+Add array rotation method

lib/arrays/index.ts

@@ -5,3 +5,4 @@ export * from './range'
 export * from './zipArrays'
 export * from './zipArraysLongest'
 export * from './partitionArray'
+export * from './rotateArray'

lib/arrays/rotateArray.ts

@@ -0,0 +1,36 @@
+/**
+ * Rotate the elements of an array by an amount specified.
+ * Essentially increments the index of every element by the amount,
+ * and elements at the end wrap round to the start.
+ * @param arr array to rotate
+ * @param amount number of elements to rotate by (default: 1)
+ * @returns the rotated array
+ *
+ * @example rotateArray([1, 2, 3]) === [3, 1, 2]
+ * @example rotateArray(['a', 'b', 'c'], -1) === ['b', 'c', 'a']
+ * @example rotateArray(['🍎', '🍐', '🍋'], 2) === ['🍐', '🍋', '🍎']
+*/
+export const rotateArray = <T>(arr: T[], amount: number = 1): T[] =>
+  arr.map((_, i) => arr[((( -amount + i ) % arr.length) + arr.length) % arr.length])
+
+
+// Tests
+if (import.meta.vitest) {
+  const { it, expect } = import.meta.vitest
+
+  it('works for example 1', () => {
+    expect(rotateArray([1, 2, 3])).toEqual([3, 1, 2])
+  })
+
+  it('works for example 2', () => {
+    expect(rotateArray(['a', 'b', 'c'], -1)).toEqual(['b', 'c', 'a'])
+  })
+
+  it('works for example 3', () => {
+    expect(rotateArray(['🍎', '🍐', '🍋'], 2)).toEqual(['🍐', '🍋', '🍎'])
+  })
+
+  it('works for amounts higher than the array length', () => {
+    expect(rotateArray(['a', 'b', 'c', 'd'], 6)).toEqual(['c', 'd', 'a', 'b'])
+  })
+}