feat(mode): Add array mode function (#222)

Author: anddago

src/index.js

@@ -82,6 +82,7 @@ import BitwiseAnd from './BitwiseAnd'
 import copyArrayByValue from './copyArrayByValue'
 import timeSince from './timeSince'
 import first from './first'
+import mode from './mode-array'
 
 export {
   reverseArrayInPlace,
@@ -168,4 +169,5 @@ export {
   copyArrayByValue,
   timeSince,
   first,
+  mode,
 }

src/mode-array.js

@@ -0,0 +1,31 @@
+export default mode
+
+/**
+ * Original Source: https://stackoverflow.com/a/1053865
+ *
+ * This method will return the element with the highest occurrence in an array.
+ *
+ * @param {Array} array - The array
+ * @return {*} - The element which has the highest occurrence
+ */
+function mode(array) {
+  if (array.length === 0) {
+    return null
+  }
+  const modeMap = {}
+  let maxEl = array[0]
+  let maxCount = 1
+  for (let i = 0; i < array.length; i++) {
+    const el = array[i]
+    if (modeMap[el] === undefined) {
+      modeMap[el] = 1
+    } else {
+      modeMap[el]++
+    }
+    if (modeMap[el] > maxCount) {
+      maxEl = el
+      maxCount = modeMap[el]
+    }
+  }
+  return maxEl
+}

test/mode.test.js

@@ -0,0 +1,23 @@
+import test from 'ava'
+import {mode} from '../src'
+
+test('mode in an empty array', t => {
+  const array = []
+  const expected = null
+  const actual = mode(array)
+  t.deepEqual(actual, expected)
+})
+
+test('mode in an array of string elements', t => {
+  const array = ['apple', 'pear', 'banana', 'pear']
+  const expected = 'pear'
+  const actual = mode(array)
+  t.deepEqual(actual, expected)
+})
+
+test('mode in an array of int elements', t => {
+  const array = [1, 2, 3, 4, 3, 5]
+  const expected = 3
+  const actual = mode(array)
+  t.deepEqual(actual, expected)
+})